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

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> of 0.12deg at a thickness of 10 nm. The thetas <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> reduced with a decrease in GdFe thickness and the sign of thetas <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> switched from positive to negative at a Gd-Fe thickness of 6 nm or thinner. Coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) was maximum and saturation magnetization (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) 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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c0_P-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AP</sub> = -3.3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c0_</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AP-P</sub> = 4.3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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.