# What is Magnetoresistance: Definition and 11 Discussions

Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in bulk non-magnetic metals and semiconductors, such as geometrical magnetoresistance, Shubnikov–de Haas oscillations, or the common positive magnetoresistance in metals. Other effects occur in magnetic metals, such as negative magnetoresistance in ferromagnets or anisotropic magnetoresistance (AMR). Finally, in multicomponent or multilayer systems (e.g. magnetic tunnel junctions), giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), colossal magnetoresistance (CMR), and extraordinary magnetoresistance (EMR) can be observed.
The first magnetoresistive effect was discovered in 1856 by William Thomson, better known as Lord Kelvin, but he was unable to lower the electrical resistance of anything by more than 5%. Today, systems including semimetals and concentric ring EMR structures are known. In these, a magnetic field can adjust the resistance by orders of magnitude. Since different mechanisms can alter the resistance, it is useful to separately consider situations where it depends on a magnetic field directly (e.g. geometric magnetoresistance and multiband magnetoresistance) and those where it does so indirectly through magnetization (e.g. AMR and TMR).

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1. ### Magnetoresistance and the Corbino disk

My answers so far are: a) J=I/(2*pi*r*t) b) u=J/ne=I/(2*pi*r*t*n*e) c) F=IB/(2*pi*r*t*n), in theta direction (polar coordinates) d) This is where I am stuck. I understand the example for motional emf with a rod moving through a magnetic field but I'm not sure how to apply it to this scenario...
2. ### I Causality of magnetoresistance

I am currently doing a research project on the topic "Anisotropic magnetoresistance" for which I have referrred various textbooks. All the textbooks state that for this phenomenon to be observed, it is necessary for the object to have more than one carrier type. This has been explained...
3. ### A High-field Hall effect and magnetoresistance

I'm reading Mermin's Solid State Physics, chapter 12: The semiclasssical model of electron dynamics. I know the current density from the ##n## band is $$\mathbf{j}=(-e)\int_{\text{occupied}}f(\epsilon_{\text{n}}(\mathbf{k}))\frac{d\mathbf{k}}{4\pi^3}\mathbf{v}_{\text{n}}(\mathbf{k}).$$ In...
4. ### I Why Is Negative Magnetoresistance Possible in Dilute Magnetic Alloys?

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...
5. ### How a Magnetoresistive Sensor Works

Hi guys I am a new member here so I am looking for feedback on the quality and clarity of this post as well as a solution to the problem. If there are any suggestions as to how I can improve the format or wording of the question I am always looking to get better. On to the question, I am...
6. ### B Resistivity tensor and Magnetoresistance

Hey everyone, I'm currently trying to understand the resistivity and conductivity tensor of a 2D sample. If a current carrying metal bar is placed inside a magnetic field the Hall Effect comes into play. I tried to search for explanations on how to obtain the resistivity tensor of the metal bar...
7. ### Role of Mn in Magnetoresistance of Perovskite

Good Day everyone! right now I'm searching for possible research in magnetoresistance properties of perovskite. So far, i already know the effect of Mn in Perovskite, it enhance the ferromagnetic properties of the material. And Manganites in Ferromagnetic State possessed magnetoresistance in...
8. ### Magnetoresistance and Fermi surfaces

There seems to be relation between Fermi surfaces and magnetoresistance, but I guess because I don't have a clear picture of fermi surfaces,I have problem understanding this relationship. Also I have heard about open and close fermi surfaces and saturation of magnetoresistance which I can't...
9. ### Room temperature positive magnetoresistance

I've achieved positive magnetoresistance (MR) in CNT composite thin films with a small percentage of Fe in it. Fe injects spin polarized electrons into CNT. But +ve MR means that resistance is increasing with magnetic field. But due to injection of spin polarized electrons the current has to...
10. ### Magnetoresistance in semiconductor

First off, I'm pretty sure I won't be able to get a definite answer here, just looking for some suggestions. In a physics lab last week, we observed some anomalous effects. First off, let me describe what we did. We were looking at the Hall effect using SiAs with an As concentration approx...
11. ### What is the typical resistance for GMR in 3-layer Fe-Cu-Fe configuration?

for giant magnetoresistance with 3 layers suppose Fe-Cu-Fe, and suppose we take room temperature (300K) and moderate layer thickness (eg Fe = 30 Amstrong, Cu = 20 Amstrong), what is the typical magnetoresistance we get? I mean the maximum resistance (in ohms) when the magnetization of the FM...