Theory of magnetization damping
The ability to control the dynamics of magnetic materials is critical to high performance electronic devices such as magnetic field sensors and magnetic recording media. Magnetization reversals associated with both writing and reading magnetic media must occur on nanosecond or faster time scales. Minimizing read/write errors requires these media to be critically damped. Conversely, lowering the noise floor of magnetic field sensors is equivalent to reducing damping in these systems.
In some samples, the damping is dominated by extrinsic effects like sample inhomogeneities, but even perfect ferromagnets have unavoidable intrinsic loss mechanisms that cause dissipation of the magnetic dynamics. Experimental investigations, have demonstrated the ability to vary the intrinsic damping rate by alloying. However, the ability to predict the changes in damping is hindered by the fact that the important damping mechanisms have not been identified and no quantitative calculations of the damping rate have been done.
By carrying out first principles calculations of damping in Fe, Co, and Ni, we have identified the primary loss mechanism in transition metal ferromagnets as a concerted effort of spin-orbit coupling and electron-lattice scattering. We have shown that this damping pathway has two contributions, which have roughly opposite temperature dependencies, one proportional to the electrical conductivity and the other to the resistivity. The competing contributions give rise to a minimum in the damping rate, which agrees well with the measured minimum in these samples. Identification of the dominant damping mechanism and demonstration of the ability to calculate it should greatly help the pursuit of materials with properties that are ideal for each application.
| λmin (109 s-1) |
FMR data | calculation |
|---|---|---|
| bcc Fe <100> |
0.88 | 0.54 |
| hcp Co <0001> |
∼1 | 0.76 |
| fcc Ni <111> |
2.7 | 2.1 |
Identification of the Dominant Precession Damping Mechanism in Fe, Co, and Ni by First-Principles Calculations
Spin-orbit Precession Damping in Transition Metal Ferromagnets
Mark D. Stiles
Keith Gilmore - Montana State University
Yves Idzerda - Montana State University
Online: October 2007
Last Updated: February 2008
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