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Questions tagged [ferromagnetism]

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Exchange stiffness for HCP

I am studying the exchange interaction, which can be described with the Heisenberg Hamiltonian: $\hat{H} = -\sum_{i,j}J_{ij}\hat{\mathbf{S_i}}\cdot \hat{\mathbf{S_j}}$ In the framework of constant ...
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0answers
15 views

Difference between domain size and correlation length in ferromagnetic materials?

I am getting confused about different length scales in magnetic materials. I understand that the correlation length for a ferromagnetic materials is defined as <(s(x)−<(s(x))>)(s(y)−<(s(y))>)>...
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1answer
29 views

Is there a minimum field required in order to start magnetizing an initially unmagnetized ferromagnet?

The question Would a compass with unmagnetized needle work? never seems to have been resolved, due to getting bogged down in a number of sub-issues where different people made seemingly contradictory ...
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4answers
2k views

Would a compass with unmagnetized needle work?

We know that the needle that is used in a compass is a permanently magnetized ferromagnetic material and commonly steel is used. If we used an unmagnetized iron needle instead, would it still align ...
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2answers
79 views

Magnetic levitation against Earnshaw's Theorem?

Given six strong magnets, what if we fix three of them to a table in a simple, horizontal, equilateral triangle-like formation (with their north poles sticking up), and the other tree to the points of ...
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1answer
32 views

What is Magnetic Intensity? [duplicate]

While studying about the magnetic properties of matter, my book defines this vector as $\vec{H}=\dfrac{\vec{B}}{\mu_0}-\vec{M}$ where $B$ is the magnetic field and $M$ is the intensity of ...
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Is the effective magnetic moment defined for substances that follow the Curie-Weiss law?

The effective magnetic moment is defined as follows: \begin{equation} \mu_{eff} = \left(\chi_M \frac{3kT}{N_A\mu_0\mu_B^2}\right)^{\frac{1}{2}} \end{equation} where $\chi_M$ is the molar magnetic ...
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0answers
51 views

Negative Eigenvalues of the Hessian

I am calculating the eigenvalues of the Hessian for a ferromagnetic system. My energy has the zeeman term, a nearest neighbor exchange term, and a dipole-dipole term. I create the hessian where my ...
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2answers
29 views

Is voltage basically the measure of the strength (or density) of an electromagnetic field? And does an increase in voltage increase the amperage?

I have been in the process of fully understanding what is generally accepted as truth by the scientific community regarding voltage, watts, and amperage. Most engineers seem to say to simply use the ...
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1answer
26 views

Does a magnet lose more potential when (passivley) magnetizing another metal?

Does a magnet lose more of it's magnetic potential when (passively) magnetizing a second (ferromagnetic) metal compared with simply being left alone for the same amount of time it took?
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2answers
44 views

How fast do the magnetic domains align with the external field?

Let say we bring a normal (not super strong) magnet near sort of an unmagnetized iron block. 1) Do the magnetic domains align instantly? Does it make any difference on magnetization strength if we ...
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2answers
47 views

A question about magnets, energy, and forces [duplicate]

Following my first lecture on magnetism today, I'm left with just one question my lecturer couldn't answer. Imagine a 1 kg magnet supporting its own weight stuck to a vertical surface, resisting ...
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1answer
65 views

Frustrated Ising model

Consider a 2D Ising model with nearest neighbour, and second nearest neighbour interactions $\mathcal{H}= -J_1\sum_{\langle ij\rangle}\sigma_i \sigma_j-J_2\sum_{\langle\langle ik\rangle\rangle}\...
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0answers
51 views

Broken symmetry Ising model

Consider an Ising model for a 2D square lattice where we have interactions for, let's say nearest neighbours and second nearest neighbours $$\mathcal{H}=-J_1\sum_{\langle ij\rangle}\sigma_i\sigma_j-...
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0answers
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Interpretation of the group velocity for a magnon

Consider a ferromagnetic one-dimensional Heisenberg chain with an anisotropy in the $z$-direction $$H =-\frac{|J|}{2}\sum_{i,\delta} \mathbf{S}_i \cdot \mathbf{S}_{i+\delta} + K \sum_i S^z_i.$$ The ...
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2answers
84 views

Why are domains not formed in paramagnetic materials?

Why are domains formed in ferromagnetic materials, but not in paramagnetic ones?
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0answers
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Rotation of sublattices in Anderson's AF Ground state

I was reading the Anderson 1952 paper (An Approximate quantum theory of the Antiferromagnetic Ground state). In section IV it computes the total spin of a sublattice, and one of the results that he ...
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1answer
68 views

How to understand the elementary excitation of spin density wave?

From Ch.4 of Interacting electrons and quantum magnetism by Auerbach, the elementary excitation of spin density wave can expressed as: $$\alpha^\dagger_{k+}=\cos\theta_kc^\dagger_{k\uparrow}+\sin\...
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1answer
41 views

Microscopic and macroscopic description of spin waves

Hamiltonian Consider the one-dimensional Heisenberg ferromagnet specified by the Hamiltonian $$H = -\frac{|J|}{2}\sum_{i,\delta} \mathbf{S}_i\cdot \mathbf{S}_{i+\delta}.$$ Here $i$ labels the spin ...
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2answers
88 views

Does ferromagnetic material decrease magnetic field intensity in surrounding area?

I have a doubt regarding behaviour of ferromagnetic material. I know that magnetic fields are said to increase in intensity inside bulk of ferromagnetic material, or converge into them. Does this ...
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1answer
28 views

Is there a maximum frequency at which hysteresis appears?

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 ...
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0answers
11 views

What is ferromagnetic resonance? How is it related to size of the sample and can it enhance magnetostriction?

I am trying to understand ferromagnetic resonance. What exactly is meant by the term? I imagine this is to do with changes in the magnetisation of the sample, but is there an increase in peak ...
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1answer
30 views

Demagnetising $H$ field

If we have a permanent magnet we know that we have a $H$ field opposite in direction to the residual magnetic field $B_r$. The $H$ field causes a demagnetisation, but how does it do it? We know that ...
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2answers
45 views

How Ferromagnetism occurs

When researching magnets it seemed that the main difference between ferromagnetic and paramgnetic elements was that ferromagnets stay magnetised after a magnetic field is removed. This then lead me to ...
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1answer
11 views

Confusion of small detail with uniformly magnetised sphere?

I have a rather pedantic question regarding the boundary condition for a uniformly magnetised sphere in vacuum. I know how to derive the effective magnetic charge density $-\rho_m=\nabla\cdot{\bf M}=\...
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15 views

Relaxation spectrum and time dependence of magnetic moments

Consider a thermally isolated ferromagnetic crystal above but near its Curie temperature in a bias field such that the magnetization is essentially saturated. Now remove the bias field as fast as ...
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0answers
10 views

Ballistic FET with channel made of ferromagnetic semiconductor

How do I find the characteristics, features, and differences of a standard ballistic FET (Field Effect Transistor) if the channel is made of a ferromagnetic semiconductor. Any papers/leads on how to ...
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4answers
126 views

Why doesn't magnetic attraction increase infinitely when distance reduces

I am not a physics guy, but I am from science background. However, I do not remember the famous explanation of this old school puzzle which our physics teacher used to ask. I searched on the internet ...
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0answers
87 views

Why do diamagnetic substances align perpendicular to the field

My textbook says that Diamagnetic substances align their longest axis perpendicular to the field in uniform magnetic field while paramagnetic substances align their longest axis parallel to the field. ...
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0answers
60 views

Correlation length

I am working with the spin-1/2 quantum antiferromagnet Heisenberg model. I have found literature about the correlation length of this model for 2D. However, what would it be in 1D? I have the ...
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1answer
24 views

Intuition of why total magnetic field decreases with air gap?

Consider two simple magnetic circuits shown below. Both are made of ferromagnetic material but the right one has also an air gap. If we close the switch $S$ and we wait long enough, the magnetic ...
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0answers
46 views

Can we have a spin glass in the one-dimensional Heisenberg hamiltonian with nearest neighbours only?

Consider the one dimensional Heisenberg Hamiltonian of the form \begin{equation} H = - \sum_{<i,j>} J_{ij} \mathbf{S}_i \cdot \mathbf{S}_j \end{equation} with nearest neighbour interactions. ...
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0answers
83 views

How to mathematically represent Néel state

Néel state is (approximate) ground state of anti-ferromagnet in which nearest-neighbor spins are align in opposite direction i.e. $$\uparrow\downarrow\uparrow\downarrow\uparrow\downarrow\uparrow\...
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Hubbard Model: Mean field theory and ferromagnetism

For the single-band Hubbard Model, I want to write down a mean field theory for the possibility of occurrence of ferromagnetism in the ground state. For the model given by $$\hat{H} = -t \sum_{\...
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1answer
73 views

Can the $s=1, m_s=0$ member of the spin triplet state lead to ferromagnetic alignment?

Ferromagnetism corresponds to the parallel alignment of spins, and it is said that for ferromagnetic alignment one requires the spin part of the wavefunction must be in one of the three symmetric ...
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0answers
44 views

Ising model compared to real ferromagnets?

I have simulated lots of systems with the Ising model, 2D. I have created plots of magnetisation, energy, heat capacity, magnetic susceptibility as a function of temperature etc. with a Monte Carlo ...
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0answers
10 views

How long does it take for a magnet to rotate to being parallel with magnetic field from Helmholtz coil?

In a physics project, we're making a Helmholtz coil, and placing a magnet orthogonal to the magnetic field from the coil. When the coils are turned on, the magnet will rotate to align with the coils ...
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0answers
36 views

what is sp-d exchange interaction?

what is the origin of sp-d Exchange interaction in magnetic materials and how it changes when transition metal is doped with zinc oxide?
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2answers
257 views

Why does hysteresis occur?

The existence of domains is a necessary condition for ferromagnetic materials to exhibit the phenomenon of hysteresis. But how are domains responsible for the phenomenon of hysteresis? What is the ...
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1answer
107 views

why do soft magnetic materials have narrower hysteresis loops?

If I wanted to reduce hysteresis losses in a system, I know that I would need to choose a ferromagnetic core made from soft magnetic material. Do soft magnetic materials have smaller permeability ...
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35 views

Can an Ising model on a sparse hypergraph exhibit ferromagnetic order at finite temperature?

Suppose I have an Ising model defined in terms of a growing family of hypergraphs $G_n$ on $n$ vertices, where each vertex represents an Ising spin and each hyperedge represents a $(\geq 2)$-body ...
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1answer
71 views

Nuclear fusion/fission vs. magnetic characteristics of Iron

Is the fact that Iron is attracted to magnets in any way related to the fact that it is also the element occupying the singular periodic table position where the chains of nuclear fission and fusion ...
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26 views

Hopping could save the kinetic energy of the system

In exchange theorem, it is well known the ability to hop could save the kinetic energy of the system. First I would like to ask how is that? This statement has been taken granted for so long, people ...
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1answer
20 views

Is a transition from multidomain to single domain a phasetransition?

Is the transition from a multodomain state to a single domain state a phase transition? E.g. in a ferromagnet as a function of field from a multidomain state at low fields to a single domain state at ...
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27 views

Help with Unusual Mean Correlation

I've been working on a variation of the Ising Model that tries to account for quantum fluctuations in the lattice. After doing a some calculations I calculated the mean correlation $<\sigma_i \...
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1answer
171 views

What are some good textbooks on material and crystal physics?

I am looking for good physics textbooks on materials and crystal physics, I do not mind if they are a bit general but they must cover useful topics. However, the specific topics I would like some ...
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26 views

Induced current by demagnetization

Take a ferromagnetic conductor (with a non-zero $\vec{M}$ magnetization, regardless of $\vec{B}$). It is known that ferromagnetic materials can be partially demagnetized by a mechanical shock (for ...
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1answer
39 views

What is the Physical Process of Corrupting a Magnetic Key Card and Is There a Detectable Difference Between a Corrupted and Non-Corrupted Card?

I was just watching the BBC show Sherlock, S3E3: His Last Vow and I got to the part where John and Sherlock are breaking into the penthouse office. The technique Sherlock employs to get into the ...
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1answer
56 views

Problems with understanding conductors in electrostatic equilibrium

I watched a few videos on conductors in electrostatic equilibrium and all I understood is that the charges stick to the surface of the conductor. So does that mean if I have a copper wire with no ...
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55 views

Dependency of $\mu_r$ vs $B$ of ferromagnetic material

How $\mu_r$ will change in a specimen of ferromagnetic material as the flux density is increased from $0$ to $2.5T$ ? [Given: Saturation Magnetisation of the ferromagnetic material is $8000$ Gauss] ...