# Is it possible to have a magnetic diode?

1. Oct 14, 2012

### haael

I wonder: do there exist "magnetic semiconductors" and magnetic diodes and transistors? Normal electrical semiconductors rely on the fact that there are positive and negative charge carriers. Magnetism does not have monopole charges, so it will not be possible to construct an isolated region of a magnetic semiconductor, but maybe it is possible to have an indivisible magnetic semiconductor junction, in the same sense that you can have indivisible magnetic dipoles despite lack of the monopoles?

What is a magnetic analogue of electric potential? Is there something analoguous to electic capacity?

Do there exist some laws that forbid existence of magnetic semiconductors? If not, have they been researched or even invented?

2. Oct 14, 2012

### Staff: Mentor

Before you think about magnetic semiconductors and more advanced elements: How does a magnetic conductor look like? It conducts magnetic charges. How do magnetic charges look like? We don't know.

Magnetic vector potential

I think you have to define what you mean with "magnetic semiconductors" first. "Something which can be called semiconductor but somehow uses some magnetism" is not a description.

3. Oct 14, 2012

### Q-reeus

First two hits on a Google search: "en.wikipedia.org/wiki/Magnetic_semiconductor" [Broken] "wyvern.phys.s.u-tokyo.ac.jp/f/lecture/srrc/SRRC_DMS.pdf" [Broken]

Last edited by a moderator: May 6, 2017
4. Nov 21, 2012

### wvphysicist

I doubt if this is relevant but the words bring it to mind.
While researching magnetic amplifiers I once wondered if an easily saturated toroid wound with many turns on one winding (a) and biased by another similar winding (b) with a steady DC current, would act as a diode when winding (a) is exposed to AC. So I made the device and observed the result with an oscilloscope. The answer is no. The current waveform is distorted but while there is a large current when the device is saturated, that doesn't last long and there is a long part of the cycle during which the current is small but in the opposite direction. This was a definite disappointment.

5. Nov 22, 2012

### haael

Thank you for refreshing this thread.

@Q-reeus
No, I didn't mean that. I'm not talking about an electrical semiconductor that exhibits ferromagnetism, but about some material that allows magnetic polarization in only one direction.

@mfb
I was referring to the analogy between the electricity and magnetism often exploited in engineering. Magnetic field is analogous to the electric current. We can say about magnetic resistance, the analog of Kirhoff's law and so on. We can for sure have magnetic conductors, magnetic SEM, magnetic resistors and magnetic inductors (which happen to be the same thing as electric inductors, which serves as the connection between electric and magnetic circuits).

Usual hard magnets will be the analog of electrical superconductors.

My question is: does it go further? Could we have magnetic capacitors and magnetic semiconductors?

As for capacitors I think the answer is no, because of lack of magnetic charges. But what with semiconductors? Do there exist such materials that can alter magnetic field in some odd maner, for instance allowing magnetic diodes and transistors?

A magnetic diode in my view is a material with this property: if we have a magnetometer and we shield it with the "diode" on one side then when we put one pole of a magnet near that shield the magnetometer will show a usual magnetic field, but if we flip the magnet and use another pole, then the magnetometer will show zero.
So it is a one-way shield for magnetic field.

@wvphysicist
Hard magnets are like superconductors. I wonder if we could see any phenomenons similar to a superconductor-metal junction in your experiment.

6. Nov 22, 2012

### chill_factor

no this does not work because you're thinking of 2 different things. one is rectifying a current (flow) of particles obeying Fermi-Dirac statistics. that's a diode.

magnetic field is not analogous to an electric current. electric current is exactly what it says it is: a particle flow. that's why there's *fluid analogs of electricity*. Fluids are also a flow of particles obeying Fermi-Dirac statistics.

ok, so tell me what particle makes up a magnetic field and its flow properties? What is flowing and how does it flow? Only if you have a flow can you talk about current. If you're talking about shielding from a field, that's not a current.

whats a magnetic conductor? the other name is "high impedence surface". Doesn't sound like a conductor anymore does it?

7. Nov 22, 2012

### Enthalpy

Haael, beware the similarity with electric current is very limited. You're overstretching it.

A magnetic material polarized near saturation is a magnetic rectifier. Use AlNiCo if you want both the magnetization and the saturated permeability in one material. AlNiCo won't let the induction increase easily beyond saturation, but reducing it is rather easy.

wvphysicist, you didn't see an asymmetric effect on the voltage because voltage results from the derivative of the flux, so over one flux cycle, the mean induced voltage is zero. But if measuring the induction or the flux, say with a Hall sensor, you would see an asymmetric effect, with the induction dropping more easily than increasing.

Could the asymmetry be obtained near zero induction? Not that I know. Some sensors, especially the fluxgate, rely on the assumption that the magnetic material used is perfectly symmetric.

This is a difficulty only for homogenous materials. If you combine several parts, some hard saturated in one direction, others magnetized in the other direction without hard saturation, I'm confident you can get an asymmetric behaviour near zero induction.

Less direct: take an anisotropic permeability - thin parallel lines of isotropic material if you wish. Put a strong permanent field at +45°, and put a field and observe the induction at -45°, the H-B curve will be non-linear.

8. Nov 23, 2012

### wvphysicist

If you are interested in materials properties you should read up on superfluids. Helium 4 and helium 3 have a host of interesting properties from vortices to second sound. Some of these phenomenon have only recently been discovered like the acoustic oscillation in a capilary between two resoviors. I believe I read about it in a recent Physics Today. Have fun.