Ferromagnetism, electrodynamics and field theory

[Babcock McGee]

Hi all,

I'm a bit confused about ferromagnetism (and I've come to realize that I'm not the only one)! I'm currently studying electrodynamics and field theory in general to solidify my understanding of such, but permanent magnets and ferromagnetic materials seem to be often ignored in the literature. I'm comfortable with charged body scenarios in the presence of magnetic fields, and the creation of magnetic fields by moving charges, etc., but I'm unable to make predictions or construct field equations involving permanent magnets, and also completely unable to understand how a magnet seems to do work by picking up an iron nail.

Before this gets too verbose, here's the bottom line: Could someone refer me to reading on the fields resulting from permanent magnets, and interaction of ferromagnetic materials with magnetic fields? I'm really interested in this from an engineering perspective, so while reductive explanations (e.g. magnetic domains as microscopic current loops) are interesting, I'm really looking for theory which will facilitate design and prediction at the macro level, ideally a set of equations.

Thanks.

p.s. The main book I've settled on is Dynamic Electromagnetics by Paul Diament. Any opinions?

 

[marcusl]

Sorry, I'm not familiar with the engineering literature. I would say that you should study the theory (M, B, mu, chi) to do a proper job of understanding applications. It won't take you long if you've mastered the fields of moving charges. As for physics texts, take a look at Reitz and Milford, they cover the material in one chapter that is straightforward and quite applied (for a physics text...).

The problem with magnetic fields and ferromagnetic materials is that analytic methods fail for all but the simplest cases. This is the domain of finite element and similar codes, which are used extensively by anyone working in magnetics (whether it be microscopic read/write heads or huge iron shields for magnetic resonance imaging). There is a gigantic literature on numerical methods and applications.

As for analytic calculations, Smythe, Static and Dynamic Electricity, calculates the field from a magnet with a gap and also the lifting power of a horseshoe magnet under simplified conditions. These should get you started.

 

[astrokreng]

Hi there,

I can understand your confusion about ferromagnetism and its relationship to electrodynamics and field theory. While these topics may seem separate, they are actually closely related and can be better understood by looking at the underlying principles.

Ferromagnetism is a property exhibited by certain materials, such as iron, cobalt, and nickel, where they can become permanently magnetized when exposed to a magnetic field. This is due to the alignment of their atomic magnetic moments, which creates a macroscopic magnetic field. This phenomenon is not fully explained by classical electrodynamics and requires a deeper understanding of quantum mechanics.

In terms of field theory, ferromagnetism can be described using the concept of magnetic domains, which you mentioned in your post. These are regions within a ferromagnetic material where the atomic magnetic moments are aligned in the same direction. The overall magnetization of the material is then a result of the combined effect of these domains.

When it comes to the interaction of ferromagnetic materials with magnetic fields, it is important to consider the concept of hysteresis. This is the lagging of the magnetization of a material behind the applied magnetic field, and it is a result of the energy required to switch the alignment of the magnetic domains. This is what allows magnets to do work, such as picking up an iron nail.

In terms of resources, I would recommend looking into books on solid state physics, as well as electromagnetics and magnetism. Some popular titles include "Introduction to Solid State Physics" by Charles Kittel and "Electricity and Magnetism" by Edward Purcell. Additionally, there are many online resources and videos that can help deepen your understanding of these topics.

In terms of the book you mentioned, "Dynamic Electromagnetics" by Paul Diament, it is a good resource for understanding the fundamentals of electromagnetics, but it may not cover ferromagnetism in depth. I would suggest supplementing it with other resources specifically focused on magnetism and ferromagnetism.

I hope this helps clarify some of your questions and provides a starting point for further exploration. Good luck with your studies!