Questions tagged [magnetic-moment]

The magnetic moment of a magnet is a quantity that determines the force that the magnet can exert on electric currents and the torque that a magnetic field will exert on it. A loop of electric current, a bar magnet, an electron, a molecule, and a planet all have magnetic moments.

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Classically, if the magnetic moment of a particle is aligned with a time-varying magnetic field, can its spin flip?

Consider the time-varying magnetic field: $$ \mathbf{B}=B \tanh{\Big(\frac{t}{\tau}\Big)}\hat{\mathbf{z}}. $$ If the magnetic moment (which is proportional to the angular momentum) of a particle at $...
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Can the spin of a spin-$1/2$ particle flip in a time-varying magnetic field?

Given that the state of the particle at time $t=-\infty$ is $\left|S_z^+\right>$, a magnetic field of the form $\mathbf{B}=B \tanh(t/\tau) \hat{\mathbf{z}}$, the Hamiltonian is $H=-\vec{\mu}\cdot\...
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How are these “supplementary” or “satellite” Helmholtz coils used?

Three mutually orthogonal pairs of Helmholtz coils can be used to produce a fairly uniform magnetic field of arbitrary direction within a certain volume, and/or to null/cancel an external field (e.g. ...
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When does $\nabla \times B =0$?

In my lab, I use electromagnets to apply a magnetic gradient force to lots of very small (superparamagnetic) nanoparticles embedded in an elastic medium. I believe that these can be treated as ...
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Why magnetic dipole moment are important

After reading the Chapter 35 of Halliday Resnick and Krane's Physics, which is the section on magnetism in which magnetic dipoles are introduced, I still don't understand why the particular quantity ...
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Permanent magnets - Attraction with no repulsion

I have some permanent "refrigerator" magnets and noticed that, though they attract the refrigerator, they also attract each other (there is only one side available for the magnet, the other side has a ...
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Reversing magnet polarity to increase/decrease Eddy currents?

I have a cast iron wheel with magnets around the inner radius as a braking mechanism. If I were to add additional magnets around the outer radius, would the amount of Eddy currents increase or crease ...
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Magnetic Dipole from 'Current' in LC Circuit

We can work out the 'current' in an LC (series) circuit by creating and solving an ODE: $$I\frac{1}{LC}+\ddot{I}=0$$ This provides us with a sinusoidal resonant response to any initial current. ...
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Increasing Eddy current induced within surface by attaching a magnet on surface

Magnets are commonly used in magnetic exercise bikes as brakes for increasing resistance: where the black wheel is a piece of cast iron. I was wondering if (significantly) more eddy currents would be ...
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Joining poles of bar magnet

What happens when 2 poles(i.e. noth and south) of the same bar magnet joined to each other to form circular loop?
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Why are there sine and cosine in the magnetic dipole moment (in the torque formula) of a rotating conductor loop?

I'm trying to redo the textbook example in magnetostatics. The current carrying loop is affected by a magnetic flux in the ax→ direction. While trying to find the torque on sides ab and cd for figure ...
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Does the magnetic field line passing along the axis of a bar magnet ever reaches to South Pole?

Consider a bar magnet, and the magnetic field line that goes through its axis and through the center of its north pole and thus follows a straight line path out of the magnet. Will this line ever be ...
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Simplification of an expression with gamma matrices [closed]

I am trying to understand the details of the calculations involved in determining the electron's anomalous magnetic moment to second order: the $\alpha/{2\pi}$ term. There is just one step, where an ...
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Special relativity constrains massless electric dipoles, but not massless magnetic dipoles?

Discussion in comments on the two questions linked below leaves me confused about the following point. We expect a magnetic or electric dipole to make a field that has some universal transformation ...
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Why is a current carrying loop considered a dipole?

I am unable to understand why a current carrying loop is considered a dipole. Why exactly is it called a "dipole", which two poles are we referring to and how do those two poles function as the north ...
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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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If I use a magnet to levitate another magnet, where is the energy coming from?

Imagine I use one static magnet to levitate another magnet indefinitely. This levitating magnet is in a narrow tube that wont allow it to rotate and get attracted. So it will keep levitating forever, ...
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What happens while breaking a Bar magnet?

If we have a bar magnet and we break it as shown below Then as per the image we get two bar magnets But does this happen instantaneously or there is some time lag between this process. Or simply, Can ...
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Why is Ampère's law violated if there are no fringe fields?

What's wrong in this diagram? The reason is this: magnetic field lines between the two poles of magnet are perfectly straight in the given diagram, which is not possible. Fringing effect of the ...
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Magnetic moment of hydrogen atom in weak magnetic field from hyper fine structure

So I need some help with this question, which is formulated: "Calculated the total magnetic moment of a hydrogen atom in the ground state in a weak magnetic field which arises from hyper fine ...
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What happens when a bar magnet is cut in half?

What happens when a bar magnet is cut perpendicular to its axis of magnetization? On searching the internet, there a lot of people who suggest pole reversal occurs and the cut ends repel each other, ...
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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 ...
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How do electrons actually move in the Stern Gerlach experiment?

As I understand it, the Stern-Gerlach experiment discovered: Fire an electron horizontally through a vertical magnetic field. Then, beyond the acceleration $e \textbf{v}\times \textbf{B}$ due to its ...
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Magnet going through a current carrying loop

Consider a small magnet that is suspended just above a conducting fixed loop placed. The magnet is oriented perpendicular to the axis of the loop and is released to fall under gravity and at the same ...
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How can neutrinos have a magnetic moment in spite of being neutral and elementary?

How can neutrinos have a magnetic moment in spite of being elementary (as opposed to a neutron) and electrically neutral (as opposed to a proton)? How can it even be defined, and measured?
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Why Earth is like a magnetic dipole?

Earth’s magnetic field is mostly caused by electric currents in the liquid outer core, which is composed of conductive, molten iron. Loops of currents in the constantly moving, liquid iron create ...
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Intuition on Magnetic Dipoles and Magnetic Moment

1) Magnetic Moment in terms of magnetic poles: According to Wikipedia, " Magnetic poles always come in pairs, their forces partially cancel each other because while one pole pulls, the other repels. ...
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Derivation of Bohr magneton; how is the angular momentum derived if not from spin?

I'm trying to understand the derivation of the Bohr magneton $m_B$. The Bohr magneton is a calculation of the magnetic moment of a charged particle with some angular momentum. Generally, magnetic ...
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Force caused by the magnetic field on the electron spin

I have read there are two ways to express the force caused by a variable magnetic field over a magnetic moment depending on the source of the magnetic moment since it can come from a dipole or a loop ...
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How to explain spin-spin relaxation in MRI/NMR in terms of quantum mechanics?

I noticed two approaches to explanation of MRI/NMR. The most popular classical approach exploits the notion of magnetization vector and Larmor precession. Everything then is described as oscillations ...
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Why is the spin magnetic moment of an electron equal to the orbital magnetic moment of a hydrogen atom?

The intrinsic magnetic moment of an electron is equal to the magnetic moment that we obtain by effects of orbital motion of a hydrogen electron in the lowest shell (1 Bohr magneton), using classical ...
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How is the electron $g$-factor determined?

I found a description of the experiments at CERN where a Penning trap is used to to determine the g-factor but I could not find the value of the radius of the circle of precession, nor could I (surely ...
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How to see s, p, d, and other band in the band diagram? Is it possible?

I am reading this book, to understand magnetism in material. It is stated there that the d-bands overlap the next higher s-band. I am aware about Hund's rule. How to see that in the band diagram? ...
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Positive and negative magnetostriction

We had the experiment demonstrating magnetostriction. We used interferometer to detect any length changes. We put the ferromagnetic material inside a coil and apply axial field. While telling about ...
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B-field and H-field opposing inside ferromagnets

I was studying Ferromagnets from several books where the authors would just state that its a notable feature of ferromagnets that, in an external B-field, the H-field opposes the B-field inside the ...
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What is going on inside this disc

I recently saw a video of a copper disc repelling paper pins which I suppose are made up of steel. By watching the video carefully in slow motion, I feel there is something inside this copper disc (As ...
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Inductive sensor - How does it work?

I can't understand how the system sketched here physically works: 4 = permanent magnet, with residual magnetization $B_r$ 6 = ferromagnetic core with a coil around it 7 = ferromagnetic toothed ...
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Diamagnetic materials with negative susceptibility?

I have been learning about magnetostatics, and from reading about the existence of diamagnetic, paramagnetic and ferromagnetic materials I was under the impression that a limiting value for magnetic ...
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Surface current density (magnetic materials)

In deriving the boundary conditions for $H$ at the boundary between two media, my lecturer stated that "since there is no conduction (free) current on the Surface... the tangential components of H are ...
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How is the Magnetic flux density derived from the curl of the vector potential?

I have two questions. Firstly, how is the equation solved after taking the curl of A(r) here. How did they arrive at the final expression for B(r). I tried taking the product rule for curl, but got ...
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Can you make electricity from the bound charges in magnets?

Magnetostatics is the study of magnetic fields in systems where the currents are steady. If inside magnets that give off magnetic fields there are bound charges, is there any possible way to make them ...
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Evaluating Magnetic Dipole Moment Integral in Spherical Coordinates

I need to evaluate the $z$ component of the magnetic dipole moment integral for a current distribution, which is given by the following: $$\mathbf M = \frac 12 \int_V \; \mathbf r \times \mathbf J \; ...
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Is neutrino really a point (fundamental) particle?

Having a non-zero magnetic moment, was a proof for neutron to not to be fundamental particle. Now we have enough literature or research work over neutrinos that have proved that neutrinos, being a ...
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If the magnetic force observed is $q \vec{v }\times \vec{B}$ then how do stationary magnets attract each other?

My theory is that it is because of random motion of electrons of atoms inside the magnet but if it truly random then all forces must cancel out also is the force really enough to attract huge magnets.
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Electric and magnetic dipole

How does an electric dipole and magnetic dipole physically realizable? By feeding a wire with current does that become a dipole?
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Why does silver lose its magnetic moment? [duplicate]

By the Gerlach-Stern experiment, the silver atom has a net magnetic moment. But silver as a metal is not magnetic. Or more precisely, it does not show any permanent magnetic moment. What is the ...
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Are magnetic surface current real?

In the book "Introduction to Electrodynamics, 4th edition" by Griffiths, the author says, I quote from page 278 : (...) We call it a "bound" current to remind ourselves that every charge is ...
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Diamagnetic Materials and their relation with temperature

What happens when a diamagnetic material is intensively cooled, considering the fact that Curies law doesn't hold good for diamagnetic materials ? What will be the effect on its magnetization ?
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What's the EM field inside a rotating magnetized sphere?

I'm looking for the analytical expressions of the magnetic and induced electric fields inside a rotating uniformly magnetized sphere. If the sphere isn't rotating, the electric field is 0 everywhere, ...
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Difference diamagnetism and antiferromagnetism

What are the main differences between diamagnets and antiferromagnets? I found out that $\chi_\text{dia} < 0$ and $\chi_\text{antiferro} > 0$, but as far as I understood, they behave pretty much ...