I know that when spin is pumped from the FM layer under FMR, the angular momenta is transferred from FM layer to NM layer, which results in increase in damping constant as well as FMR linewidth in bilayer system.
I am curious to know the next steps
1. How the pumped spin results in linewidth broadening? I is it broader for metallic or insulating NM layer?
2. will there be no spin pumping if there is no carriers in the NM layer? on the other hand no linewidth broadnneing?:
3. I am not able to visualize these steps. Can someone please help me?
Thank you Eric,
My means does spin pumping or the gilbert damping will depend on the carrier concentration of non-magnetic layer?
eg. metal has larger carriers than semiconductor non-magnetic layer.
Line broadening is a well understood thing in FMR. you do not have to employ complicated names to understand. Line broadening occurs in polycrystalline materials due 1) to inhomgenieities, different magnetic phases or inclusion of non magnetic phase2) conductivity 3) porosity 3) strong anisotropic materiaals. In a single crystal which was my speciality, things are clearer. Just anisotropy and the presence of ions with strong spin-orbit coupling would widen the line width. The simple reason being the precession energy is transferred via spin-orbit coupling to the lattice which absorbs thus dampening the resonance or in otherwords the precession of the spins. These are well explained in any text bookof the 1970s.
Thank you sir for your comment. My confusion is that if One uses semiconducting layer as a nonmagnetic layer. and perform temperature dependence of FMR(linewidth). As carrier concentration in semiconductor decreases with temperature. will it result in decrease in linewidth with decreasing temperature? is there any connection of linewidth with the number of carriers or mobility of carriers?
This may not happen because still it would be conductiing and inhmogeneous broadening would be there. Also the mag material itself without the additonal SC layer would show T dependence of the line width. In all probabilities the line width will increase as T goes down. Reason, inc in anisotropy , magntic inhomogentities etc.
Sir, how to separate this in-homogeneous broadening and determine the linewidth due to spin injection? could please give some idea?
Thank you
It does not look to me as easy. IN short I have no idea.
One might try this however. The inhomogenous broadening generally occurs due to nonmagnetic incluions, porosity. They generally scale with M. Try if your line widht scal with M as T is lowered. IF the increase is more then other mechanisma is operating. Note that this just a forst approximation method.
Spin pumping and spin injection became very fashionable terms recently. On the other hand, the FMR linewidth is quite successfully described by (older?) theories not taking into account either spin pumping or spin injection. Roughly speaking, the FMR linewidth increases when loses increase. The side effect is change in absorption line shape (see Dysonian lineshape). Some loses may be caused by eddy currents, be it in the sample or in the neighboring NM (but conductive) layer. Joule heat, roughly speaking. Spin injection or spin pumping results in creating of the spin current. Here no electric charge is involved, so there is no simple Joule heating. I haven't seen yet any solid theory relating loses with spin currents. This is certainly not easy, as the Maxwell equations do not incorporate spin currents.
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