Science Buddies: "Ask an Expert"

Hi I am wanting to do a science fair project on how ferromagnetic metals' spontaneous magnetization are affected by temperature. I also want to compare the results i get to a graph of blochs law which is M(t) = Mo(1-BT^(3/2). I have learned that blochs law is accurate from temperatures well below the metals curie temperature, but is not that accurate close to the curie temperature. I was hoping to use nickel because I can get closer to its curie temperature (627 K or 669 F) to compare. Although I probably can only get the nickel up to 500 F because that is how hot my oven gets so I don't know if I will see any results. I have built a simple magnetometer from the website: https://www.kjmagnetics.com/blog/diy-ma ... bww4z8OgCN

It works on magnets but not very well for pure ferromagnetic metals like iron and nickel. I was wondering why since they are ferromagnetic so they should have their own magnetic field and show up on the magnetometer? Also do you maybe know places where I can get larger amounts of ferromagnetic materials that have a magnetic field so I can do my experiment or if my experiment will even work?

Also one last question: I was wondering what other cool experiments I could do with magnetics. I'm really interested in the magnetic fields and quantum mechanics and physical properties of naturally magnetic materials and was wondering how I could incorporate all of that into a science experiment.

Hi - sorry that you did not get a reply to your post earlier. A few things:

1. I'm not very familiar with spontaneous magnetization of ferromagnetic materials based on temperature, but my understanding is that most ferromagnetic materials (such as iron filings) will NOT have their own magnetic field at room temperature. They require the presence of an external magnetic field (from a permanent magnet or electromagnet) at which point they will develop their own induced magnetic field. Depending on the strength of the applied external magnetic field, when that field is removed, the ferromagnetic material may retain some residual magnetization. So, if you just bring your homemade magnetometer near a chunk of iron that hasn't been magnetized yet, it isn't going to measure any magnetic field.

2. McMaster-Carr is a website that may sell raw stock of various metals: https://www.mcmaster.com/. You could also go to a hardware store and buy large bolts, but it may be difficult to figure out exactly what the metal composition of the bolts is.

3. Note that most smartphones have a built-in magnetometer, and you can download apps like Phyphox and Physics Toolbox that give you access to the magnetometer readings. That may not be needed if you have already built your own, but it's an option.

Hope that helps!

Sorry I forgot to add - we have tons of projects on our site, I don't think we have any on quantum mechanics but if you search our site for key terms like magnets or magnetism, you should find some other ideas.