Negative Magnetoresistance?

In summary, Beal-Monod and Weiner explain the negative magnetoresistance observed in dilute magnetic alloys as a result of spin-flip scattering of conduction electrons off impurities. They argue that this process should be forbidden due to the decrease in energy of electrons at the Fermi level caused by the applied magnetic field.
  • #1
georgeD123
2
0
A free electron gas would have zero magnetoresistance; it takes two carrier types to get ordinary magnetoresistance, which is always positive in sign.

Beal-Monod and Weiner explain the negative magnetoresistance found in very dilute magnetic alloys, in terms of the spin-flip scattering of conduction electrons off the impurities.

Their argument seems to be the following:

Consider an electron scattering off of a magnetic impurity, in the presence of an applied field, in the case where μH<kT.

An electron in initial state ki,↓ scatters into state kf,off of an impurity, whose spin is reduced to compensate. Conservation of energy gives ki=kf.The net change in electron energy should be -2μH.

Since only electrons within kT of the Fermi Level can participate in scattering processes, they claim that this process should be forbidden. I don't see why.

The original energy was at least εF±kT. The final energy should then be εF±kT-2μH. If μH<kT, then this should be guaranteed to remain within kT of the Fermi Level.

What am I thinking about wrong? Thank you!

(For what it's worth their exact words are "the final spin-up electron has a total energy (kinetic+Zeeman) less than εF by at least 2μH-kT." I just can't quite make the signs jibe or I am thinking about something wrong. Thanks!)
 
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  • #2
You are right in your thinking that the final energy of the electron should remain within kT of the Fermi level. The authors are referring to the fact that the electron energy at the Fermi Level is not necessarily the same as the average energy of all electrons. When the magnetic field is applied, the average energy of the electrons decreases by 2μH, but the Fermi energy remains unchanged. Therefore, the electrons at the Fermi level experience a decrease in energy of at least 2μH-kT, which may be less than the kT limit required for scattering. This is why they argue that this process should be forbidden.
 

What is negative magnetoresistance?

Negative magnetoresistance is a phenomenon where the electrical resistance of a material decreases when subjected to a magnetic field. This is the opposite of what is typically observed in most materials, where resistance increases with magnetic field.

What causes negative magnetoresistance?

Negative magnetoresistance is caused by the movement of charged particles, such as electrons, in a material when subjected to a magnetic field. This movement changes the way the material conducts electricity, resulting in a decrease in resistance.

What materials exhibit negative magnetoresistance?

Materials that exhibit negative magnetoresistance are typically those with high electrical conductivity, such as metals, semiconductors, and carbon-based materials like graphene. These materials also have a high mobility of charged particles, allowing for the movement necessary for negative magnetoresistance to occur.

What are some potential applications of negative magnetoresistance?

Negative magnetoresistance has potential applications in various technologies, including magnetic sensors, data storage devices, and magnetic random access memory. It can also be used to improve the performance of electronic devices by reducing power consumption and increasing sensitivity.

How is negative magnetoresistance measured?

Negative magnetoresistance is typically measured using a four-point probe technique, where a small current is applied to the material and the voltage drop is measured. This measurement is then repeated with a magnetic field applied, and the change in voltage is used to calculate the change in resistance. Other methods, such as magnetotransport measurements, can also be used to measure negative magnetoresistance.

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