IAmA Magnet Engineer. I answer questions about magnets for a living.

Fucking magnets, how do they work? And I don't wanna talk to a scientist. Y'all motherfuckers lying, and getting me pissed.

Hang on a second. I have to go check and see who won the betting pool for how long it would take this meme to surface. ;) Unavoidable with this job title...

I'll play the role of a literal-minded engineer and answer it: Richard Feynman's explanation is still my favorite. YouTube link. How much of an answer is enough to satisfy you? You can sense is irritation and impatience with the question.

This video explanation from the Veritasium guy is also pretty good. Ultimately, though, it comes to the same conclusion as Feynman: it just does. That's the way the universe seems to work.

Your company's trademark image used what we all see as the classic magnet, totally iconic. Why do we no longer use this shape today? While I'm sure efficiency has a role to play in it, was there some fundamental flaw in the original design that has since been realized?

It's all about coercivity. That's the fancy word for how much a magnet resists getting demagnetized in a magnetic field.

Like when you magnetize a steel screwdriver by wiping a magnet along it, but it doesn't seem to last. That's because the steel has very low coercivity. The magnetic field it has tends to actually demagnetize itself.

Early magnets had lower coercivity. The horseshoe shape (and the use of a steel keeper) were fancy ways of adjusting the magnetic circuit to keep the thing from demagnetizing itself.

Alnico magnets, like those found in home alarm systems and electric guitars, are better, but still not as high coercivity as neodymium magnets. You find Alnico in horseshoes or long cylinders to prevent demagnetization.

Neodymum magnets aren't just stick-to-the-fridge strong, they're also harder to demagnetize. Like, you need an MRI machine magnetic field to do it. It also means you can have a thin disc magnet, which wouldn't stay magnetized with old magnet material.

This article has some better explanation with pictures: Why are magnets shaped like horseshoes?

Ironically, that horseshoe shape of our mascot isn't really needed for neodymium magnets.

Hey! You work for K and J? I've designed your stuff into our products before.

Mainly the 34lb 1/4" 1.5x1. They are very brittle though!

Yes, that's a continuous challenge. People see shiny magnets and assume that they're strong as stainless steel. It's not true at all. They're more like a brittle ceramic that's actively trying to repel itself apart....

What do you feel the future of magnetics is? Say we have (US) an economic war with China and our source of Rare Earth elements are cut off. Are we back to old fashioned magnets or is there any future tech coming around that reduces foreign reliance?

This is an interesting geopolitical/market question, wrapped up in technical details that matter. It's not a simple subject.

In fact, this sort of thing has a long history. Back in the 1970s, Samarium Cobalt magnets were the only kind of rare earth magnet. I guess most of the cobalt in the world came from Congo, and unrest there drove the prices through the roof. This dependence spurred the research that led to neodymium magnets.

Neodymium magnets are in everything from our iPhone headphones to our weapons systems. We do need them. Historically, we haven't had a neo magnet industry here in the US. It has been offshored since its invention in the 1980s, really.

The answers to questions like this are complex. For example, dysprosium is used to make higher temperature grade magfnets often used in hybrid vehicles. So, access to dysprosium is an important issue. Still, there are technical solutions that can be used around this. One could use a taller, non-high-temp magnet instead of a smaller high-temp magnet. The implications are about weight, size and cost.

What is the strongest magnet ever on earth and what does it do?

The strongest permanent magnet material is a neodymium magnet. We haven't discovered or made anything stronger.

Now, when you start getting electricity involved, people have made much stronger magnets. Think scientific research, particle colliders, etc.

I think the 45 Tesla (!) magnet down at the National High Magnetic Field Lab in Florida is as big as they come. For reference, keep in mind that a 16 T field is strong enough to levitate water, like the levitate a frog experiment.

Which is the world's biggest magnet?

Also, if we keep splitting a magnet in half, till which point will it retain it's magnetism?

When you split a magnet in half, the two halves are now two separate magnets. Each half has a north and a south pole.

How small can we keep splitting? Down to the level of magnetic domains. In this article about magnetization direction, a picture of magnetic domains shows that the size of these domains in neodymium magnets is about 0.00025" across or so.

Break it down smaller than that, and I think you'll be demagnetizing them.

Thank you for answering my second question.

I'll ask the first one again. Which is the biggest magnet (on Earth)?

0sigma answered it: The largest by size is the earth. It's one big magnet, though it's quite weak. See The Earth is a Magnet.

What's the biggest neodymium magnet? The largest sizes sold by K&J Magnetics is a 4" square block. It's incredibly powerful, scary dangerous to handle, and much larger than most folks would ever need for any reasonable application.

much larger than most folks would ever need for any reasonable application

But I'm sure we could find plenty of finger crushing unreasonable ones.

In any case, what are 4" magnets of that strength used for? I'm assuming that if they make them then at least one person has wanted one for some reason, any idea as to that reason?

Usually, it's some kind of science/study. Two of these magnets with a gap between them can be a great way to make a strong magnetic field in a little space, without the hassle and dangerously high currents of electromagnets.

I've also heard of them used further apart to make a strong magnetic field over a larger area. One experiment had them around a nest of turtle eggs, to see if their departure direction was affected by the magnetic field direction.

If a magnet is place against a 1/8" plate of stainless steel OR 1/8" of aluminum, which would diminish the magnetic field on the other side the most? If there is a difference, roughly what kind of % difference would you expect in the magnetic field interference between the stainless steel vs. aluminum?

Thanks for any help with this!!

PS I've purchased magnets from these guys -- good prices and fast shipping.

OK, let's assume you're talking about getting the most pull force to some steel object. We'll stick your magnet to the fridge door, with the 1/8" thick aluminum in between. How does this affect the strength?

The permeability of aluminum is about the same as air, or wood or paper. So, the strength is about the same as if I placed an 1/8" thick stack of paper between the magnet and the fridge. Strength depends on the distance between the magnet and the steel.

If you start introducing ferromagnetic materials (stuff magnets stick to), you'll see less pull force. If your stainless steel is ferromagnetic (some kinds are, some kinds aren't), it will shield the magnetic field from reaching the fridge. You could end up with little to no force with a 430 stainless steel. Or, with a non-ferromagnetic 316 stainless, it could be the same as your aluminum setup.

Is it possible to have a bicycle where a magnet holds the wheel into place causing zero friction between the frame and wheel?

Magnetic bearings sound like a good idea. Little to no friction sounds appealing right? When you actually sit down to design the nuts and bolts of how it works, it's difficult to get real benefits from it.

Two magnets won't simply levitate to float above one another. It needs some stabilizing factor, usually a mechanical stop. This introduces friction, which you wanted to avoid in the first place!

Can a magnet ever lose its strength? What would cause that?

Sure, a magnet can get demagnetized. How? It depends on what kind of magnet we're talking about. Generally, high temperatures or strong magnetic fields can partially or fully demagnetize a magnet.

Neodymium magnets are commonly demagnetized by high temperatures. While they're the strongest kind of magnet around, they have some of the lowest operating temperatures. Many start losing strength above about 80°C or so.

You can also smack them with a hammer right?

Yes, I've heard that a lot. I've demagnetized a slightly magnetized piece of steel this way. I've even affected an Alnico magnet with a hammer.

I've tried to characterize how impacts demagnetize neodymium magnets and failed pretty miserably. It seems that the strength of the impact that you need to see any meaningful demagnetization is strong enough to break the magnet.

"Look, I've demagnetized the magnet"

"Dude, it's in 18 pieces on the ground. No kidding it's demagnetized."

How many magnets would it take to make a floating bed and how much would it cost?

Also, what's the largest magnet you guys make that an average dude can buy?

Can you use repelling magnets to levitate a bed? Yes, but it isn't easy or cheap.

Floating magnets won't just levitate over one another. You need some mechanical constraint to keep them from flipping around side ways and attracting to one another. That would be some kind of vertical rail to keep the bed aligned.

When you start to do the math on how many magnets you need, it gets into some big/dangerous/expensive magnet territory. Mess with the Repelling Magnet Force Calculator for some numbers. Assume a gap of maybe 1" or so, and you're quickly talking about magnets that are 2-3" in diameter, with pairs at each corner of the bed.

Is it possible/practical to make a "bowl" lined with magnets so that an opposing magnet (or spaced grid of magnets) can "float" without sliding away? Is preventing the flipping without mechanical restraint the hard part?

Nope, the bowl idea doesn't work. Earnshaw's theorem proves that you can't do it with any combination of permanent magnets.

could you explain this a bit?

It seems like you could line the entire perimeter of the bed with diagonal magnets (mostly vertical, but tilted towards or away from the center of the bed somewhat). Fixing magnets in a floor-mounted unit that align with the bed-magnets using opposite poles should repel the bed.

This arrangement intuitively seems like it would handle the limited side-loads while supporting the larger against-gravity loads. But I understand someone has studied this and shown that magnetic fields don't work this way. Could you clarify why in layman's terms?

When thinking about magnets in this kind of setup, it's easy to think of them as mechanical springs. There's a force pushing them apart. In reality, though, this mechanical spring analogy doesn't tell the whole story.

A pair of repelling magnets are unstable. That is when you have them slightly offset from one another, they feel forces that tend to push them further offset (and rotate around).

Aren't you losing business by doing this?

Nah, I don't think so. Now more people are thinking about magnets! ;)

Magnets, how do they work?

Scroll down to the reply below 19Hawks' question...

What is Neodymium like in its natural state? How is it mined/extracted?

Neodymium is a rare earth metal, though it's not particularly rare. It's dug up in a mixture of other metals. The German who discovered it called it mischmetal, because these rare earths tend to be found all mixed up.

Digging it up is the easy part. The challenge is the baths that are used to pull out each individual element into pure form. It's a chemical process that can be pretty messy.

What are some of the most common misconceptions abbot magnets that people have in your opinion?

Well, there's the idea that magnets somehow store energy, like a battery. Not so.

A lot of the discussion about how magnets will work ends up comparing a pair of magnets to a mechanical spring. It's an analogy that most people can relate to. It works well, up to a point. It's not completely perfect though, so when you think of them this way, what magnets actually do starts to seem pretty unintuitive.

How does a metal detector detect non-ferrous metals?

Eddy Currents!

I'm not a metal detector expert, so I'm probably over-simplifying this, but...

The end of your metal detector is a coil of wire. It runs a current of electricity through it, so the thing acts like a magnet.

When you pass a magnet over a chunk of, say, aluminum, the moving field induces currents in the aluminum. Those currents act like little weak magnets. By carefully sensing those magnetic fields with the coil, the detector sees those currents -- sees the aluminum.

I have a legit ELI5 question:

Where does all the energy come from? if I hold two opposite magnets together they push apart.. does this happen forever or will they slowly "run out of power/polarity?"

I might get a little physics on you, hung up on jargon, but here goes: It's wrong to think about this as some kind of exertion of energy. No energy is being expended by the magnets when you hold two of them together, repelling one another.

Let's go with the mechanical spring analogy. If you squeeze a spring between your hands, it pushes back on both ends. If you hold it squeezed, it keeps pushing back. How long will it push before it runs out of energy? Forever, or until it rusts away.

The spring isn't spending any energy to push your hand.

What is your favourite type of magnet?

Mine is the comedy ones that Wile E. Coyote uses that he buys from Acme.

Neodymium, of course! Though, anything from Road Runner is awesome.

Follow up question: If Coyote had used a nedymium magnet, would he have had better luck catching the Road Runner?

This is something we really need to see. I'll happily donate magnets to the episode...

What are some fun things I can do with the microwave emitter from a household microwave?

I tend not to recommend taking apart a microwave to get the strong magnets inside. That's not just a, Hey, buy neodymium magnets pitch. It turns out that there's some nasty stuff in that magnetron assembly. Something in there is made with beryllium oxide, which in dust form, is really bad for you. Think: lung cancer.

I'm not an expert in which part in there is bad, but not knowing, I tend to stay away.

are there people who have an actual fear of magnets? like getting their fingers smashed and not able to pull two strong magnets apart.

For that, we have the EMERGENCY Magnet Separator!!!

Are there ways magnets can improve the future of space travel?

There's long been the idea of electromagnetic cannon shooting things into orbit. For a number of reasons, like incredibly high G forces, this hasn't quite turned into a practical method to get to orbit.

I like some of the low-cost magnetic solutions we see happening. For example, there are low-cost mini-satellites that use a strong neodymium magnet to control the orientation of the magnet. In orbit, the magnet tends to align with the earth's magnetic field. It's a good way to make the thing have a predictable attitude without all the hassle of propellent and thrusters controlling it.

Simple and cool!

I have a 1/8" diameter magnet (one of your D21B-N52 in fact) glued inside a 1/8" hole in a resin model. Then, somehow, another magnet gets in the hole and they are now stuck together inside the hole. What is the best way to get the second magnet out?

Somewhat related, what is the best/strongest way to glue those magnets to resin?

This can be challenging. Rapping it a little with taps/impacts can help break glue bonds.

One trick I use is to clean the visible surface, then glue another magnet to it. Stick a taller D28 magnet to it with a dab of superglue on it. The superglue sets in less than a minute, and can sometimes be strong enough to yank the first magnet out.

What first attracted you into becoming a magnet engineer?

Aw, you're making this too easy! I'll field this question though. There's currently so many electric puns flowing through my head it Hertz.

Actually, I used to work on hardware design of electronic products. I sort of found this work without planning to work with magnets, though it has been really great.

How are Neodymium magnets made?

How Neodymium Magnets are Made...

Are there any special restrictions on shipping magnets, or are your precautions self-enforced?

Both. There are rules by both the IATA (International Air Transport Association) and the FAA about this, which limit the amount of magnetic field that can be around the outside of a package.

See this about how we work to stay within those limits.

You would have been useful in my class on magnets. Whats the difference between diamagnetic, paramagnetic, ferrimagnetic and ferromagnetic materials? Emphasis on the dia- and para-.

Ferromagnetic stuff, like iron and steel, sticks to magnets. When I have a neo magnet stuck to a paperclip, that steel paperclip temporarily acts like a magnet. I can puck up a second paperclip with it, because it's acting like a magnet.

Paramagnetic stuff isn't something I have much experience with. I think it's also a case where a material in a magnetic field is slightly attracted to the magnet. Go look at the first example on Wikipedia and they show a picture of trickling liquid oxygen. That's not something I run into every day.

Diamagnetic is when a material is repulsed by magnetic fields. Water is very, very slightly repelled by magnetic fields. This article has a good demo. There's a video there that shows the surface of water bowing in very slightly when you bring a neodymium magnet close to it.

I've seen a Youtube movie of some DIY dude that used a neodymium magnet to find studs, or, more precisely, screws in a wall. I tried this at home with some cheaper neodymium magnet myself, but of course it didn't work. What type, or what strength factor magnet would you need for something like that?

We get this question so much, we wrote an article about it!

I remember playing with a magnet kit when I was a kid, and the horseshoe magnet had a "keeper" (a steel bar you stuck to the horseshoe when you weren't playing with it) which was supposed to make the magnet last longer. How does this work? Do magnetic domains reinforce each other better when they form "closed circuits?"

Old horseshoe magnets needed a keeper to keep it from demagnetizing itself so much. Modern neodymium magnet material doesn't tend to do this, so you don't need a keeper.

In fact, that whole horseshoe shape was made to help reduce demagnetization in the first place. That's why you don't see neodymium magnets made in that shape: it isn't necessary.

How about magnetic shielding? Where are we on being able to block or reduce magnetic fields with thin materials?

I tend to divide shielding materials into two categories:

Steel and other ferromagnetic materials work well for strong magnetic fields. Near a neodymium magnet, it's often a great choice.

Some specialized metals like MuMetal can offer more attenuation (greater reductions in the field strength), but saturate at lower field strengths.

Put more practically, use steel for reducing big strong fields. Use specialized metals for the shielding can over a sensitive component that's some distance away where you might need more attenuation.

Hey, just read your blog post on the mag switch. I love the illustrations but am mildly infuriated that you did not include the field depiction of the magnets in the off position and not in the steel housing. What the heck does that look like?

Those Magswitch magnets are cool!

The last picture at the bottom of that post shows the off field. It flows out of one magnet, through the sidewalls, and into the other magnet. Not much at all reaches outside the magnet housing.

What is your personal favorite toy/fun application of magnets?

Most elegant application of magnets? (not limited to toys)

Are there any advances brewing that could soon result in dramatic new capabilities?

Ah, I like the simple stuff the best. Give kids a few magnets, and they know what to do with them. Making a magnet move around the kitchen table by secretly moving another around underneath the table just never seems to get old.

Most elegant application of magnets? Magnets are so pervasive, so everywhere in modern life, it's hard to pick a favorite. If you're into green things, maybe you like wind turbines or hybrid vehicles.

I kind of like the Internet. The information revolution has actually happened / is happening, changing lives in very substantial ways. All that information in the magical cloud is really little bits of magnetic stuff pointing up or down, in zeros and ones. No magnets, no Internet.

Oh hey are you the guy that writes the K&J newsletters? I'll have you know, your newsletter is one of the few that I don't unsubscribe from! I bought a few magnets back in college just to play around with. Magnets have always fascinated me and I ultimately got my master's degree in Electromagnetics.

I don't have a question for you, but I think you have a really cool job. Keep up the good work!

Hey, thanks for the compliment. It's a team effort, but you might say I'm the point man. We love putting them together. It's an excuse to play with magnets, and answer magnet questions at the same time.

What's the worst that anyone has hurt themselves with one or more of your magnets? (I'm one of your customers. Not criticizing, nor trying to cause panic, just curious.)

I've seen pictures online of someone who had their finger crushed between two really big neodymium magnets. He included x-rays of the completely crushed bone. One picture had his fingernail (removed from him) still stuck between the two magnets.

Those particular magnets weren't from K&J, but all big neodymium magnets are serious. Respect the magnets!

Have I got a question for you! MRI magnets: I learned about them in a neuroimaging course and haven't been able to get an answer to my question since. How are they transported if they're so damn powerful? Most modes of transportation are metal. To preempt any redditors who link me to the How It's Made episode about MRIs, thanks, but it doesn't answer my question. Thank you!

I'm not an MRI expert, so I might be making this up a little. Here's my guess.

The strong magnetic field around an MRI isn't from just a bunch of permament, neodymium magnets. There's also some kind of electromagnet in there that makes such a strong, big field. When it's not powered, it's not producing such a strong magnetic field.

There's still serious magnets in there, but not enough to be problematic in that way.

What would you say to certain people who uphold magnets as evidence of "miracles," while at the same time admitting ignorance of how they work?

There's certainly an element of the mystical and unknown associated with magnets. It's an invisible force!

Gravity is an invisible force too, but we seem to have accepted it a little easier into our minds. It doesn't have the WOW factor when an apple falls out of a tree.

Seriously, though, there's still a lot that science hasn't quite figured out about magnetic forces. It's an incredibly interesting subject.

Two repelling neodymium magnets (say 1cm square) are impossible (for me) to push together, but weaker magnets can be pushed together until both metals are touching. Is anything happening to the atoms in the respective magnets while this is happening? Does pushing them together cause permanent changes to the structure or strength of the magnetic field?

It depends on the details. In general, neodymium magnets can withstand this sort of thing without demagnetizing. In some cases, such as really thin magnets, or other kinds of magnets or high temperatures), it's theoretically possible to demagnetize a bit of a magnet. It doesn't happen often with neodymium magnets.

The last few years neodymium magnets are used in those lightweight speakers and became Popular in guitar and especially bass cabinets, is there going to be something even lighter in the future?

Neodymium magnets are incredibly small and powerful. They make tiny hard drives, tiny ear buds / speakers, etc. all possible.

They're still working their way into guitar pickups. Many are still using Alnico magnets. I hope to do a future demo on how to wind your own guitar pickup!

There's a lot of research that goes into magnetic materials. While it's hard to predict breakthroughs, there doesn't appear to be a new magnet material on the horizon. More efforts are being spent on making neo magnets more efficently, less expensively, and with a wider variety of rare earth materials.

what is the coolest thing you can do with a magnet that no one knows about?

I can't tell you, muahahaha!

Hey there, small question: If magnets are made using electricity, but you need magnets to make an electric current, then what came first? The magnet or the current??

That's a fun question. I was just chatting about this the other day here on reddit in askScience: Which process of generating electricity would be more tenable if time traveling 5000+ years back?

Do monopoles exist?

AFAIK, there is no such thing as a magnet with only one pole. All magnets have two poles, north and south.

There's a theoretical particle that some physicists describe to explain some things, but no actual magnetic monopoles have been discovered. See the magnetic monopole article on Wikipedia.

Neodymium magnets seem to be the standard used currently for wetwares, how do you feel about their use in the biohacker community?

Er, it's not something I'm rushing off to do. As a guy who handles strong magnets every day, the last thing I want is a sensitive spot in my fingertip that's pulled towards magnets!

My opinion: It's also perhaps not the greatest health choice. While they're not especially toxic, they are made up of about two-thirds iron. That thing's gong to rust inside you. I'm not keen on a rusting disc of metal inside my body.

I keep meaning to superglue a magnet to my fingernail to check out the idea. If there's any feeling of magnetic fields, that should be sensitive enough to experiment with it in a less invasive way. Of course, I'm probably missing the point. Biohacking is done for the sake of doing it.

Hey there! I'm a fella with magnets in two fingers. Although mine are cylinders instead of discs. They have a bio coating so that they won't rust or otherwise be rejected by my body. Assuming they don't get damaged that is.

Feeling magnetic fields is pretty cool, and I've used them to quickly find working or non-working electrical components. And people seem to enjoy the little bar tricks you can do with them.

But yea, as someone who handles strong magnets daily, getting them yourself would be a bad idea.

Do you find you get through a lot of credit cards?

No, you have to get magnets pretty close to erase a credit card. Though, I do leave my wallet elsewhere when handling large magnets!

I've got this vague idea for a pet DIY project, a diorama of the old WipEout games. If you're not familiar with the games, it's a racing series centred around these futuristic floating vehicles, which look a bit like this. I found out about diamagnetism, and figured this would be a handy way of getting (small) stuff to float (slightly) above a track. If I was to get two concentric toroidal electromagnets, would a small piece of diagmagnetic material be stable in between the two? And would the field be consistent around the circumference of the toroids?

Edit: lemme know if my explanation sucks and I'll draw a diagram

There's some cool levitation forces you can get with magnets, but they're often very unstable (between two magnets) or very weak.

The magnetic train demo at the end of this article shows magnets repelling, and also that you need some mechanical stabilization.

Diamagnetism over a piece of graphite provides the kind of force you're looking for, but it might be too weak.

Superconductors might do the trick, but messing around with liquid nitrogen can be a pain.

No easy answers here...

Is it possible to generate electricity from magnets?

Of course! Most modern wind turbines have big neodymium magnets inside.

On a smaller, more accessible scale, this demo of a shake flashlight shows the very basic ideas of generating electricity with moving magnets and a coil of wire.

What is the most cutting-edge application on the horizon for magnet technology that everyday consumers are not aware of yet?

Magnets are being used in biomedical research, analysis and treatment at skyrocketing rates. You won't see these magnets in consumer devices, but this medical work is really doing some groundbreaking stuff across a wide variety of fields.

Basic idea: If you have bacteria, cells or whatnot that you want to study, you might need to separate them from some fluid. You get them to eat/ingest iron nanoparticles, then you can separate them with strong magnets.

Ive had an odd question about magnets for a long time. I've never been able to find an answer to this...

How long do magnets last? More specifically, how long do magnets retain their magnetic properties?

Thanks for the AMA

It depends on what kind of magnet you're talking about. Older magnet technologies, like ceramic or Alnico magnets, can tend to demagnetize themselves over time. The devil is in the details, so how it's used, the shape of the magnet, the details of the magnetic circuit -- all these things can affect matters.

I have ceramic fridge magnets that demagnetized quickly. I also have a magnetic closure on a 40 year old dresser that still works well with a ceramic magnet inside. So, it depends.

With neodymium magnets, the answer tends to be longer. These things can retain their full strength for years, even decades without any real loss of strength. On the time scales we're talking about, issues with high temperature (will the A/C fail once in the next 3 decades?) or corrosion.

What's the largest neodymium magnet one can obtain? I've heard of ones the size of a shoebox but that just seems comically enormous and horrifically dangerous.

comically enormous and horrifically dangerous.

Well phrased. The largest sizes K&J sells are 4" square, and those fit that description. I've seen some as large as 6". That's about the upper limit.

I don't think anybody makes the equipment for larger sizes because there's just no demand for something that expensive and large.

Can you explain the different grades of Neodimuim magnets and how they are created to give greater de-mag temperatures?

Most neodymium magnets are a mix of about one-third neodymium and two-thirds iron, plus some other stuff (like Boron and a few other elements).

Higher temperature grades add a tiny bit of dysprosium in place of some of the neodymium, which makes it perform better at higher temperatures. The more Dy you add, the better the temperature range. There's some loss of strength, though, so more Dy means less strength.

Dysprosium costs a lot more than Neodymium, so higher temperature grades tend to be more expensive. [Here] is a list of common grades. The letter suffix indicates the temperature grade.

Two quesitons: 1) You mention Alnico. Is this AlNiCo, Aluminium Nickel Cobalt?

2) Is magnetization and demagnetization caused by a physical change in the orientation of the magnetic molecules of in the object? IFAIK heating ferromagnetic things up and letting them cool can make them lose their magnet properties, presumably because all the magnetic dipoles in are pointing every which way. If this is correct I ask this. What research is being done into binding molecular magnetic dipoles in an atomic structure. Like graphene sheets or Silicon wafers. I'm not suggesting these substances, I'm thinking about a repeating uniform structure which has molecular magnetic dipoles in a lattice of other atoms acting as a scaffold. Is this even possible theoretically?

Yes, Alnico magnets are magnets made of Aluminum, Nickel and Cobalt. They were commonly used before neodymium magnets were invented. They're still used, though less so in some applications.

Your mention of magnetic domains and direction are probably what you're looking for. In a piece of steel, the domains are pointing in every which direction, and cancel each other out. When I stick a magnet to it, those domains are temporarily aligned in one direction, so the steel acts like a magnet.

I love this video that gets into that level of detail on the subject...

What are the biohazards, if any, for your larger magnets? I can imagine getting a finger between a big magnet and a piece of metal could cause you to lose a finger but I was thinking more in terms of possible disruption of neural activity or cell processes with long-term close exposure.

There's not a lot of clear answers in this department. When you start asking questions about how magnetic fields affect tissue or animals, you're getting into an odd area. With so many folks making some outrageous claims about magnets, it's hard to separate fact from fiction.

I know that magnets have some affect on living things. One experimenter taped a neodymium magnet to the back of a bird, and it got lost. Reasonable proof that they use the earth's magnetic field to know which way they're going.

Another interesting study found that cows in pasture tend to align themselves with the magnetic field in a specific way, but that this was disrupted to randomness near high power lines. I think the study looked at a bunch of satellite photos to catalog this.

How do I re-magnetize neodynium after melting and casting it?

With a really, really strong magnetic field. You need some pretty specialized equipment for this. Picture a coil of wire around your magnet and run an insanely high current through it for a split second to make a magnetic field strong enough.

Most people don't do this. Most get neodymium magnets in the fully magnetized state.

What did you study in school? I'm currently a mechanical engineering student, and this all seems pretty interesting. I'm going to my materials science class next, so maybe I'll ask my professor about it.

I majored in mechanical engineering, though an electrical engineer could do my job as well. There's a great big field of engineering work that's electro-mechanical that both mechanical and electrical engineers find a lot of good work in.

It's ironic that I chose mechanical because it seemed more understandable and related to my experiences. I could replace a clutch but not build a circuit, so it seemed like a good idea. So far in my engineering career, though, I seem to have been working with electronics and magnets a lot!

Pick a major you like, but be broad in your application of it. Some of the coolest projects I've worked on were more software than anything, like the Magnet Calculator.

What are some interesting effects (if any) that magnetic fields have on the human brain?

I can't find it right this second, but there's one video out there that uses incredible strong magnets near the brain and it causes stuttering! There's lots to learn in there...

These are the closest thing to magic I've truly ever seen. That being said, I have heard of people trying to make "power generators" out of magnets. Are they just blowing smoke or is this truly possible to any extent?

While the search for free energy continues, I've never seen a working example of a device that generates electricity or continuous motion from permanent magnets alone. It seems that physics and thermodynamics say that such a device is not possible.

Note that most electric motors and generators do contain permanent magnets, but they really only convert mechanical work into electricity or vice versa, and always with some energy losses.

Of course, that doesn't prevent folks from experimenting with ideas like this anyway. Experimentation is good, and playing with magnets will help folks find their own answers. I wouldn't expect anything soon, though.

What do you believe is the future of magnets?

That's hard to say. I'm not on the cutting edge of magnetic research, though from what I read, there aren't any breakthrough magnetic materials about to be discovered. Though, really, it's hard to predict breakthroughs, so what do I know.

Engineers are still figuring out ways to use current magnet technologies. I still see neodymium magnets getting into applications where they haven't been before, so that change is still happening. It's certainly shrunk the size of some of our electronics!

What is the most "do not attempt at home" dangerous thing you could conceive of doing with magnets? For a friend....

If you haven't handled really strong neodymium magnets, don't buy a big one. Fingers really do get pinched and squished.

What piece of technology has the magnet not even begun to improve?

Toothpaste?

Hey I'm thinking of putting some N52 magnets on the bottom of a pair of shoes to hover in place over a sheet or slab of metal (just for fun). Would you think this would be practical/safe?

It turns out that levitation is pretty tricky. Magnets don't just float over one another. They're not stable.

Also, magnets in your shoes would attract to a steel surface, not repel.

Is there any limit right now to how much B field density and volume of the magnet?

With permanent magnets, neodymium magnets are the strongest available. If you measure the magnetic field over a single magnet, you're looking at numbers in the 1,000-7,000 Gauss range (0.1-0.7T).

If you make assemblies with magnets and steel or iron, you could see fields that are stronger, in the 1-2 Tesla (10,000-20,000 Gauss) range.

Many MRI machines are operating at the 3 Tesla range.

Since we have a limited amount of fossil fuels, do you see in the future, any form of magnets being used to propel transport, and would it be cost efficient? This video has me hoping!

The idea of magnetically levitating trains reduces friction, which does reduce the amount of energy you need to propel a train. The magnets don't provide that propulsive energy, though. You need some other form of propulsion, like electricity to make it move.

What is the force between two disk shaped magnets when the radius of one is much much greater than the radius of the other?
I was told it goes to zero, but I'm not convinced. If you do answer this, feel free to use lots of math.

Actually, in certain cases with certain geometry, this is true. More than true: I can show you an example where when you bring two magnets together, one way larger than the other, with the magnets repelling, they actually hit a point where the force drops to zero, then goes in the other direction. The north pole of one magnet is touching the north pole of the other magnet, but they're attracting. Weird but true!

See the last section of this article for a better explanation with pictures and a video.

Is there any material that can block magnetic fields?

Steel and other ferromagnetic materials can redirect magnetic fields, but not truly stop them. They are used for shielding.