It was seen that when magnetization is in the direction of current flow, resistance is minimum and vice versa. Why resistance increases when spins are aligned and why it decreases when spins are aligned in perpendicular to current direction. According to me it should be opposite.
When the magnetic field is in the direction of the current flow, the flow of electrons which denote the current doesn't experience any force(Lorentz). But the field due to the current and external field are perpendicular, giving a resulting field which affects the alignment of the spin, affecting the flow of electrons. Hence Magneto resistance increases. When the field is perpendicular the electrons do experience a force which is perpendicular to both the field and the direction of the current. The flow is that much not affected because the spins are not disturbed. If the Lorentz force, Faraday Lenz law are connected, this can be explained...
I knew the answer in 70's when I was doing Ph.D. I have forgotten the logic.
But I remember a very good reference which is a MUST for people working on electron magnetotransport.
J. - P. Jan in Solid State Physics, Ed. by F. Seitz & D. Turnbull(Academic Press, New York, 1957), Vol. 5, p 1.
The alignment of the spins are disturbed by the field present due to the flow of e's in the same direction of the field. That is why the resistance increases when the direction of current is in the same direction of the magnetic field.
The field due to the current will be perpendicular to the spins which are aligned due to the external field.
I think the coupling of the magnetic moments of the flowing electrons and and that of spins is higher when the current flows in the direction of magnetization.
Hello Vikas!
The physical origin of the magnetoresistance effect lies in spin orbit coupling. The electron cloud about each nucleus deforms slightly as the direction of the magnetization rotates, and this deformation changes the amount of scattering undergone by the conduction electrons when traversing the lattice. A heuristic explanation is that the magnetization direction rotates the closed orbit orientation with respect to the current direction. Ifthe field and magnetization are oriented transverse to the current, then the electronic orbits are in the plane of the current, and there is a small cross-section for scattering, giving a low resistance state. Conversely for fields applied parallel to the current, the electronic orbits are oriented perpendicular to the current, and the cross-section for scattering is increased, giving a high resistance stat. See the diagram in the figure demonstrating the physical origin of AMR!!!
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