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Questions tagged [ferromagnetism]

The basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets. Ferromagnetism manifests itself in the fact that a small externally imposed magnetic field can cause the magnetic domains to align and reinforce with each other, so that the material is said to be magnetized.

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Are there any "induced" forces which are repulsive in nature?

For example, London forces and induced dipole forces are both attractive forces. Additionally, when a ferromagnetic substance is placed in a magnetic field of a permanent magnet, induced magnetism ...
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Understanding the “source” of magnetic energy in a bar magnet

I’m an amateur trying to grapple around this problem of what sources the magnetic energy in a bar magnet… We know that the source of the magnetic force that a bar magnet exerts is due to its magnetic ...
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Is spin relaxation asymmetric in magnetic semiconductors?

I am considering photo-excitation in magnetic semiconductors (e.g. metal organic frameworks). The cartoon picture is like this: where there will be a spin polarization in the conduction band since ...
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How to calculate magnetic force produced by electromagnet through a medium at a distance

I am attempting to make a chessboard that has a strong electromagnet beneath the board, so that a piece with imbedded metal or magnet can move above the board. The image below is for reference only ...
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Mixed configuration of magneto-optical kerr effect

Typically there are three types of magneto-optical Kerr effect experiments: Polar, longitudinal, and transverse. These three geometries yield very different results regarding what is measured (...
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How to actually do calculations with the quantum-mechanical Heisenberg model?

The Heisenberg Hamiltonian in its simplest form is $$\hat{H}= \frac{1}{2} \sum\limits_{i,j} \hat{S}_i \cdot \hat{S}_j.$$ Normally, $\hat{S}$ is assumed to be a classical vector and from this ...
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Alignment and anti-alignment of spins in magnetic field

Let's say that we spins in a very strong magnetic field. Then, the spins want to align in the same direction as the magnetic field due to torque being exerted on the spins. However, it may happen that ...
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Showing that the ground state of the Heisenberg ferromagnet is an eigenstate of the Hamiltonian

The Hamiltonian of a Heisenberg ferromagnet in terms of $S^+, S^-, S^z$ is given by: $$H = -\frac{1}{2}|J| \sum_{i,\vec{\delta}} \left[\frac{1}{2}(S_i^+S^-_{i+\vec{\delta}} + S_i^-S^+_{i+\vec{\delta}})...
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Calculating Saturation Magnetization from Atomic Moments

I'm attempting to calculate the saturation magnetization ($M_s$) of a material based on the value of atomic magnetic moments. For instance, iron's saturation magnetization is commonly reported as 2 T (...
Physics Student's user avatar
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Ferromagnetism vs antiferromagnetism

In ferromagnetism the spins align in the same direction, but in antiferromagnetism the spins align in the opposite direction. Both are due to the so-called 'exchange interaction', with a negative ...
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Differential magnetic susceptibility v.s. magnetic susceptibility?

For a given material which has the M-H curve looks like the following figure: When I extract the magnetic susceptibility of the material, should I use the ratio between M and H, $\chi_m=\frac{M}{H}$, ...
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How would you calculate the FWHM of a point spread function with 2 peaks, such as those present when differentiating a hysteresis loop curve?

To evaluate the spatial resolution of an imaging system, it is common to take the FWHM of a point spread function (PSF) describing said system. In my case, the imaging system is Magnetic Particle ...
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Solving a PDE using $x-vt$ as a variable

So I was reading this Landau and Lifshitz paper: https://doi.org/10.1016/B978-0-08-036364-6.50008-9 The article can also be found without a paywall by just searching its title, "On the Theory of ...
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Derivation in a Landau-Lifshitz ferromagnetism paper

I was reading the following paper by Landau and Lifshitz on ferromagnetism: https://www.sciencedirect.com/science/article/abs/pii/B9780080363646500089 In the paper, the following expression is used ...
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Hysteresis curves of a ferromagnet magnetized below saturation

I am confused about the qualitative behavior of ferromagnetic materials. Referencing the diagram below, I understand that magnetizing a ferromagnet from point A to point C (its saturation ...
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Ferromagnetic substance beyond Curie's temperature

According to my textbook and various sources on internet I found that susceptibility of paramagnetic substance is related to temperature by the following formula: $$χ=Cμ_0/T$$ Susceptibility of ...
Harjot Dhillon's user avatar
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Path of magnetization in hysteresis curve from demagnetized point

In Introduction to electrodynamics David J. Griffiths 4th edition, section 6.4.2 in magnetization of ferromagnets, after we reach the saturation point (point b in the image) Now suppose you reduce ...
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Is there a name for a Heisenberg-like model, but instead of the ZZ operator, we have one that favor only spin-up-spin-up configurations?

I understand that the Quantum Heisenberg XXZ model in 1D has the form: $$\hat H = \frac{1}{2} \sum_{j=1}^{N} (J_x \sigma_j^x \sigma_{j+1}^x + J_y \sigma_j^y \sigma_{j+1}^y + J_z \sigma_j^z \sigma_{j+1}...
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Time for ferromagnet to align with magnetic field

A ferromagnet is inside a solenoid. When the current in the solenoid flips its direction, the solenoid magnetic field flips. As a consequence, the ferromagnet magnetization flips. What determines the ...
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Typically, how much could an ferromagnetic core amplify the field of a solenoid?

I have been confused by this for days. Consider a ring-shape solenoid with DC current. If we insert a ferromagetic core (cylinder) into the solenoid, how many time it could amplify the field, compared ...
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Stoner-Wohlfarth hysteresis at 0 magnetic field

There is something that is confusing me about the Stoner-Wohlfarth model. Looking at the wiki page, one sees this picture for the hysteresis loop: The angles denoted are the angles between the field ...
Andreas Christophilopoulos's user avatar
3 votes
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Hamiltonians with collective quantum spins and their ground states

This feels like it could be a undergrad/grad-school quantum mechanics course level problem, or potentially something pretty interesting. I'd be happy with either answer, but I don't know which one is ...
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Two-point-correlation in the 3D ising model

I am currently coding a 3D (Monte-Carlo) implementation of the Ising model, using the single spin-flip & Wolff algorithm. So far, I was able to calculate all the interesting observables, like $M$ ...
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The mechanism of metal capturing magnetic flux

What is the mechanism of ferromagnetic object capturing magnetic flux? For example, I learned that round metal is used in transformers to raise efficiency because the flux is carried through the metal....
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What is the difference between Curie's law and Curie-Weiss law? [closed]

Curie's Law: $$\chi_m = \frac{C}{T}$$ Curie-Weiss law: $$\chi_m = \frac{C}{T-T_c}$$ (C is Curie constant and $T_c$ is Curie temperature.)
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Is magnetic susceptibility infinite at Curie temperature for a ferromagnetic material?

By Curie-Weiss law , $$\chi_m = \frac{C}{T-T_c}$$ Where, C is Curie constant and $T_c$ is Curie temperature. If T = $T_c$ would then $\chi_m$ be $\infty$ ? But by theory , at Curie temperature the ...
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Why does the 'exchange interaction' in ferromagnetism favour parallel spins of electrons? Shouldn't the pauli exclusion principle hold?

I am trying to grasp the concept of the "exchange interaction" in ferromagnetism, specifically why it favors the parallel alignment of electron spins. Intuitively, one might expect the Pauli ...
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Are there thermodynamic reasons a super diamagnet cannot exist?

We define a super diamagnet as a substance which not only expels any internal magnetic fields but actually produces a stronger internal magnetic field in the opposite direction of the external field, ...
Sidharth Ghoshal's user avatar
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Why Curie temperature is bigger for smaller lattice in 2D Ising model

Using Metropolis algorithm, Curie temperature was calculated for square lattices with different sizes 4x4, 8x8, 16x16 and 32x32. Here Curie temperature was estimated as temperature of maximum of heat ...
John's user avatar
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2 answers
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Heisenberg ferromagnet model

I am studying some things related to the two-dimensional $xy$ model and ended up relying on the Heisenberg model to describe a ferromagnet in the presence of an external magnetic field. \begin{...
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How can a mean-field hubbard model describe itinerant ferromagnetism?

I see some textbooks showing how Hubbard model with Mean field approximation can explain ferromagnetism of band electrons(stoner theory), but intuitively I can't understand why an on-site Hubbard ...
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Calculation of the electrical resistance of an anisotropic conductor with spacially varying current density [closed]

Fist time posting here, so I apologize in advance for the terrible editing . I am trying to figure out a way to calculate the total resistance of a rectangular structure with known spatially dependent ...
Mooorshum's user avatar
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1 answer
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Ising model and the axiomatics of Statistical Mechanics

I am revisiting Statistical Mechanics to better understand models of spin glass and was wondering to what extent axiomatics of Stat.Mech. applies to an ensamble of spin configurations. In particular, ...
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Do the random-bond Ising model correlation functions decay with the disorder strength?

I'm imagining a square lattice with Ising spins on the vertices and nearest-neighbor Ising interactions. The interaction on a given bond is ferromagnetic with probability $(1-p)$ and antiferromagnetic ...
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What is the relationship between the distance of a current carrying wire and a dipole magnet's magnetic field strength?

For school, I'm doing this experiment where I measure the change in magnetic field strength, between a magnet and a current-carrying wire as a function of the distance. Online after doing some reading,...
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1 answer
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Attraction/repulsion forces between two magnets

If I have two identical magnets of equal strengths producing equal repulsive forces between them, and if I replace one of the magnets with a stronger magnet (everything else remaining the same), how ...
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Ground state of the Heisenberg XXX model with a coupling?

I have a one-dimensional Heisenberg chain with a Magnetic field with $N$ sites with $J>0$ \begin{equation} \mathcal{H} = -J \sum_{i = 1}^{N-1} \vec{S_i}\cdot \vec{S_{i+1}}- \sum_{i = 1}^N \vec{H}\...
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How to interpret Magnetic Susceptibility as the ratio of two vectors $M$ and $H$, as division of two vectors is not defined in mathematics?

Magnetic Susceptibility, denoted as χ is defined as a scalar, represents the ratio between the Magnetization vector ($\vec {M}$) and the Magnetic field strength vector ($\vec{H}$). However, in ...
Dinesh Katoch's user avatar
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2 answers
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Why does a magnet not move in presence of an electric field?

I only recently thought about this, and I can't come to any conclusion. An explanation for ferromagnets is perhaps explainable, and my teacher said Quantum Mechanics complicates things since the ...
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Rotation of spin orbit coupling matrix

In first-principle calculation, we could get different solutions for different directions of magnetization for ferromagnetic system. I want to know the details about whether or when does the SOC ...
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What is the meaning of aligned and anti-aligned spin states in quantum mechanics?

For a quantum system of two spin-1/2 particles, the spins are said to be aligned or parallel and anti-aligned or anti-parallel, if total $S=1$ (maximum value) and $S=0$ (minimum value) respectively, ...
Solidification's user avatar
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Use of Curie law in Antiferromagnetic Weiss theory derivation

When deriving the magnetic susceptibility of an antiferromagnetic (AFM) material Coey in the book Magnetism and Magnetic Materials (p.196) assumes that for one sublattice it holds true that $\chi = \...
Tomáš Maleček's user avatar
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1 answer
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Is the Ising magnet relevant for magnets?

To what extent is the Ising model for the ferromagnetic transition experimentally relevant for real ferromagnets ? For example if one quantitatively compares the magnetization versus temprature data ...
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Breaking a magnet

When a bar magnet is broken into 2 pieces, we know that the 2 new pieces also become bar magnets with 2 poles. The piece corresponding to the north pole of the unbroken magnet gets a new south pole, ...
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How is the local magnetic moment determined experimentally?

The Anderson model is contrived to explain the existence/nonexistence of local magnetic moments in metallic solutions. It is said that for a solution of A atoms in B metal, sometimes there are local ...
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Is heat treatment the only means known to man for increasing grain size in steel?

It is well known that steel grains tend to grow larger under heat treatment. Is it possible to enlarge grain size through any other means? I cannot seem to find anything via web search. If steel is ...
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Peierl's argument for 1D Ising model

I'm having a hard time understanding Peierl's argument for the non-existence of spontaneous magnetization in a 1D Ising model at $T>0$. Let the Hamiltonian be $$ H = -J\sum_{i} S_i S_{i+1}.$$ The ...
tchuncly's user avatar
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2 answers
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Metals and Magnets

A metal is attracted by a magnet when placed in it's vicinity. I was wondering if it is the metal that moves towards the magnet, or is it that both the metal and magnet move towards each other? Could ...
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Explanation of massive Goldstone modes

I'm solving this exercise with a Heisenberg Hamiltonean in linear spin-wave theory and at some point we are asked to compute the dispersion relation at $k=0$, which leads me to finding two different ...
Rye's user avatar
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Fresnel coefficients with permanent magnetism

I am familiar with the standard derivation of the Fresnel coefficients for linear magneto-dielectrics (for instance https://en.wikipedia.org/wiki/Fresnel_equations#Derivation). However, I was ...
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