Magneto-Optical and Spin-Transfer Switching Properties of Current-Perpendicular-to Plane Spin Valves With Perpendicular Magnetic Anisotropy

We evaluated the magneto-optical properties of spin-valve (SV) stacks with perpendicular magnets comprised of a Gd-Fe (4-30 nm) free layer and a Tb-Fe-Co/CoFe pinned layer, and the spin-transfer switching properties of current-perpendicular-to-plane (CPP) SVs with the perpendicular magnets. The Gd-Fe free layer had polar Kerr rotation thetas
_k
of 0.12deg at a thickness of 10 nm. The thetas
_k
reduced with a decrease in GdFe thickness and the sign of thetas
_k
switched from positive to negative at a Gd-Fe thickness of 6 nm or thinner. Coercivity (H
_c
) was maximum and saturation magnetization (M
_s
) was minimum at a thickness of 8 nm. These phenomena may be explained by an inhomogeneous Gd-Fe composition. The CPP spin valves with the Gd-Fe (10 nm) free layer had a magneto-resistance (MR) of 0.038%. The free layer of a CPP SV device was switched by a pulsed current, which exhibited intrinsic switching current densities of J
<sub>c0_P-

AP</sub>
= -3.3times10
⁷
A/cm
²
and J
<sub>c0_

AP-P</sub>
= 4.3times10
⁷
A/cm
²
with a thermal stability of 75, which is above the required value of 40. Perpendicular magnets are very useful for obtaining large magneto-optical signals from nano-magnets driven by spin-transfer switching.