What Materials Are Magnetic?

[hilbert42]

I reckon holmium deserved a mention, why is it missing?

To quote Wiki:

"Holmium, like all of the lanthanides, is paramagnetic at standard temperature and pressure. However, holmium is ferromagnetic at temperatures below 19 K (−254.2 °C; −425.5 °F). It has the highest magnetic moment (10.6 μB) of any naturally occurring element and possesses other unusual magnetic properties. When combined with yttrium, it forms highly magnetic compounds."

[DoingIsLearning]

Very cool, the site's entire 'materials' archives is really interesting as a layman in Materials Science. [0]

This kind of reminded of the sense of wonder of reading through Encarta entries in the late 90's and how I assumed the internet would look like in the future.

[0] https://sciencenotes.org/category/chemistry/materials/

[rkagerer]

That link lists the Piezoelectric Effect near the top. I wondered if there's a corollary for magnetism. I googled the word Piezomagnetic on a whim and was satisfied to find this: https://en.wikipedia.org/wiki/Piezomagnetism

[kergonath]

It is quite good. They touch on complex topics but remain understandable and provide sources for further reading. I did not see anything obviously suspect, which is rare in vulgarisation.

[FrankWilhoit]

Their example of nickel is a U. S. five-cent coin. Nickel is ferromagnetic, but the coin is 75% copper and a magnet will not pick it up.

[analog31]

Interestingly, the Canadian coins are the same dimensions, but are magnetic. US vending machines used to have a magnet that would deflect Canadian coins into the coin return slot.

When I was growing up near Detroit, merchants took US and Canadian coins interchangeably, and gave both back out as change. But the Post Office was strict about it. I managed to collect a set of King George coins -- at least the smaller ones.

[barelyauser]

But they can be picked up with right kind of electromagnetic arrangement[0].

[0]. https://youtu.be/7ZeBWJLRXqM&t=1231

[m463]

I have a shrunken nickel from these folks:

https://www.capturedlightning.com/frames/interesting1.html

Don't know if the copper figures into the shrinking...

[bediger4000]

Tungsten carbide is magnetic. I bought a "tungsten" cube from some shoddy Amazon vendor. It's a lot denser than steel, but not as dense as pure tungsten. It is magnetic. The density of the cube is in the range of tungsten carbide.

[cyberax]

> Tungsten carbide is magnetic

Pure tungsten carbide is not. You just got some magnetic contaminants in it.

This has is a good test for fake "gold" that can consist of tungsten core with a thin film of gold on top. It's pretty much impossible to get pure tungsten, so such "gold" ends up being magnetic.

[foobarian]

I got one of those too, and it came with a manifest showing that there is about 5% of nickel in the composition so not too surprising.

I would certainly be surprised if they could manufacture a pure cube (> 99.9%) for the price they sell it at :-)

[mianos]

The glue to hold the sintered carbide powder is cobalt or iron or whatever pot-metal crap they have on hand for cheap blocks. That would be where the magnetism is coming from. If it's highly magnetic you probably have little tungsten and a lot of binder.

[rowanG077]

It's probably not tungsten carbide but rather a common tungsten nickel alloy

[mjfl]

At the microscopic level, what determines whether a given set of valence elections has an excess spin, and thus an excess magnetic moment, is still determined by an empirical set of rules, called Hund's rules, instead of from first principles, iirc:

https://en.wikipedia.org/wiki/Hund%27s_rules

[csours]

https://hackaday.com/2022/09/01/iron-nitrides-powerful-magne...

Iron Nitrides

[ChrisMarshallNY]

I think I remember reading, somewhere, that liquid hydrogen is magnetic.

[ChrisMarshallNY]

Nah. Hydrogen under enough pressure, becomes metallic. I don’t think it’s magnetic, though.

[SigmundA]

So aluminum and copper are listed as not magnetic yet powerful magnets are used to separate them from non metallic materials in recycling? Seems like a semantic argument.

https://en.wikipedia.org/wiki/Eddy_current_separator

[wtallis]

> Seems like a semantic argument.

That kind of phrasing usually indicates someone doesn't understand or is rejecting a meaningful and useful distinction. Is that what you intended to do here?

The article seems to be pretty clear about how there are several different types of magnetism that can be exhibited by materials, and appropriately classifies various materials. Nothing about the existence or mechanism of eddy current separators is a counterexample to anything in the article.

[colanderman]

Any electrically conductive material is affected by eddy currents.

[dvh]

Liquid oxygen is magnetic too (I think para in this case)

[mianos]

There are very specific about including 'metals' in every statement. Yep, paramagnetic non metals are: Oxygen (commonly shown on youtube), Nitric Oxide, Boron, Sulfur and some graphites (very slight) due to delocalised electrons.

[mankyd]

That's mentioned at the bottom: "However, liquid oxygen and boron fullerenes (B80) are paramagnetic."

[m463]

Wonder if you could use that to separate gasses.

I also wonder about "sorting" atoms/molecules like Maxwell's demon:

https://en.wikipedia.org/wiki/Maxwell%27s_demon

[bsmith89]

Most interesting sentence:

> 304 stainless steel isn’t normally magnetic, but it becomes partially ferromagnetic if it’s bent at room temperature.

Anyone have a lay-person explanation for this?

[Tuna-Fish]

Iron exists in many different crystal structures in different kinds of steels. Some of these forms are magnetic, others are not. When you work the metal, such as by bending it, you can cause it to change from one structure to another.

304 is an austenitic stainless steel, and austenite is non-magnetic. But when it's cold worked, it turns into martensite, which is harder and magnetic. If you anneal it by heating it and letting it cool, it turns back into austenite.

[koolba]

Not a physicist, but I’d guess that bending the metal causes it to heat up, which in turn could make it easier for electrons to align and respond to magnetic waves.

[RavingGoat]

My smile of course :)