 # Discover and Master Ferromagnetism with Our Comprehensive Resources and Practice Problems

Recent questions in Ferromagnetism Brooklynn Hubbard 2022-05-13

## In explaining/introducing second-order phase transition using Ising system as an example, it is shown via mean-field theory that there are two magnetized phases below the critical temperature. This derivation is done for zero external magnetic field B=0 and termed spontaneous symmetry breaking The magnetic field is then called the symmetry breaking field. But, if the symmetry breaking occurs "spontaneously" at zero external field why do we need to call the external magnetic field the symmetry breaking field? I am confused by the terminology. Lexi Chandler 2022-05-10

## $M=\sqrt{\frac{4U}{3}}\varphi$where M is the ferromagnetic order parameter and $\varphi$ is the auxiliary field from the Hubbard-Stratonovich transformation. The book argues that because the above equation is correct, the mean field theory which is derived from the Hartree-Fock approach is equivalent to the the saddle point approximation formalism for H-S transformation auxiliary field Lagrangian. But I can not understand the equation. garcialdaria2zky1 2022-05-09

## I am currently studying magnetism as a part of AP Physics 2, and what confused me was that a Tesla was the unit for magnetic field strength(which decreases with distance) but it was also used to measure the strength of magnets. Why is this the case? Is there not another metric that could be used to measure the total strength of the magnet? Also, when the strength of a magnet is given in Teslas, at what point from the magnet is that number derived? Kevin Snyder 2022-05-09

## In Three Lectures On Topological Phases Of Matter section 2.1 mentioned, that:${I}^{\mathrm{\prime }}=\int dt{d}^{3}x\phantom{\rule{thickmathspace}{0ex}}\left(\stackrel{\to }{a}\stackrel{\to }{E}+\stackrel{\to }{b}\stackrel{\to }{B}\right)$correspond to ferromagnetism and ferroelectricity. And that${I}^{\mathrm{\prime }\mathrm{\prime }}=\int dt{d}^{3}x\phantom{\rule{thickmathspace}{0ex}}\left({a}_{ij}{E}^{i}{E}^{j}+{b}_{ij}{B}^{i}{B}^{j}\right)$correspondence to electric and magnetic susceptibility.Could somebody clarify, why? Yasmine Larson 2022-04-12

## If a ferromagnetic material is immersed in an alternating magnetic field at frequency $\omega$, the material will follow a hysteresis cycle at that frequency. But if that frequency is high enough, the spins will oscillate more and more, and I think it will somehow increase the temperature of the material (because in a classical picture: more frequency $⇒$ more velocity $⇒$ more kinetic energy $⇒$ more temperature.)As hysteresis only appear below the Curie temperature, if higher frequencies make the metal get hotter, there will be a critical frequency ${\omega }_{c}$, above which hysteresis won't appear. Does such frequency exists for every ferromagnetic material? Alaina Holt 2022-04-12 tuehanhyd8ml 2022-04-07