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Questions tagged [ferromagnetism]

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Ferromagnetism and induced magnetism

According to Wikipedia: A magnetic domain is a region within a magnetic material where individual magnetic moments of the atoms are aligned with one another and point in the same direction thus ...
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Ferromagnet $\leftrightarrow$ paramagnet at Curie temperature

I think it's like this: $\, m=\tanh\left(\frac{Bμ}{k_bT}\right)$. If now the temperature decreases, then $\mu$ increases, until it flattens out ($\tanh$ function). Is the a point where $m$ flats out, ...
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ferromagnetic above the Curie temperature paramagnetic?

Why is a ferromagnet above the Curie temperature a paramagnet? Considering me, it's because a paramagnet has a higher entrope and since $\frac{1}{T} = \frac{\partial S}{\partial E}$. If T increases ...
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Localization of $4f$ in rare earth and $3d$ electrons in transition metals

Is there a justification for why are the $4f$ electrons strongly localized about the nucleus in rare-earth atoms but the $3d$ electrons in transition metals extend further out from the nucleus? I have ...
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Detecting if there was a repulsion or attraction on a magnet

I would like to know if we have a way of detecting if a magnet reacts to a iron bar or attract /repel by another magnet. Would be able to see through a sensor if there was some activity in the ...
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Pauli matrices acting on creation operators in the second quantization formalism

I'm looking at some lecture notes for electron scattering taking place at a ferromagnet-superconductor junction. The idea is to start from a tight binding model, and eventually obtain the BdG equation....
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The force involved in magnetic attraction

Magnetic field causes a force to act on moving charges as in this equation: $F = qv*B$. So what is the force that causes a magnet to attract a charge-less piece of iron? or causes the like poles of ...
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Why don't all elements with unpaired electrons become ferromagnetic?

As a necessary condition, ferromagnetism in elements requires the existence of unpaired electrons. However, all elements with unpaired electrons are not ferromagnetic, e.g., metals such as aluminium ...
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Which mechanism causes ferromagnetism in iron?

There are at least three different mechanisms which can give rise to ferromagnetic order in iron. First is due to the band electrons called band magnetism or itinerant magnetism which is an exchange ...
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How is the rotation of a ferromagnetic bullet affected by a coilgun?

I've been asked a question that I'm unable to answer. It's about a coilgun, and even if it could probably be expressed in simpler terms, I'll ask it in its entirety just in case I make mistakes while ...
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Hysteresis in Magnetoresistance

I am measuring the magnetoresistance of a thin ferromagnetic film from -1T to 1T, it looks something like this - The magnetoresistance increases slightly between 0 and coercivity of the film and then ...
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Why an insufficient overlap cause vanishing exchange interaction?

Why should the exchange interaction vanish if the atoms do not have sufficient overlap in their overfunctions? For exchange interaction not to vanish, the only requirement seems to be that the ...
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Ferromagnetism - computational physics

The autocorrelation of the magnetisation is plotted for the Ising model of a ferromagnet. The critical temperature is 2.3 J/k Is this the expected behaviour? as in, it decays super fast for ...
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Coercivity of pure iron

Coercivity of 99.8% pure iron is 1 oe but that of 99.95% pure iron is 0.05 oe.Why such difference while both have same retentivity? Edit: I mean to say if both have same amount of residual magnetism ...
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Do magnets lose some form of energy while attracting each other? [duplicate]

Consider two very strong magnets, one above a wooden table, one below a wooden table. As the two magenets clamp together, wedging the tableplate between them, at least the bottom magnet will ...
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What is the explanation behind this weird hysteresis graph?

We were doing an experiment with Ferrite material to find the Curie temperature of the material. We found that at some temperature range, there are two loops at the two ends of the curve. What is the ...
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1answer
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Why do spinning electrons generate magnetic dipole moments?

Can the spin of electrons generate currents? If not, how does it create magnetic dipole moments?
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Dielectric vs. Ferrite

I am currently taking electricity and magnetism. And I do not understand something, what is the difference between ferrite and dielectric materials. I understand that they each correspond to one of ...
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Re-Radiation from a ferrite rod antenna: Phase relative to the incoming signal

I am working through a problem involving interactions between multiple closely located ferrite bar antennas. I am seeing energy re-radiated from the various antennas coupling into the other ...
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Parameters Affecting Demagnetisation

What parameters will affect how a ferromagnetic material is demagnetised? Assuming that only changing fields will induce demagnetisation (although I suppose I could well be wrong on that one), what ...
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How does one electron or spin see the other in a ferromagnetic material?

QM tells us that only one component of angular momentum is measurable which conventionally taken to be Lz= 1/2. The other two components have an uncertain magnitude and direction and this is usually ...
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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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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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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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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
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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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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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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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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
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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
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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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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
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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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Why are domains not formed in paramagnetic materials?

Why are domains formed in ferromagnetic materials, but not in paramagnetic ones?
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1answer
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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
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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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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
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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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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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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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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
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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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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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4answers
280 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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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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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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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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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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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 ...