Abstract
The work focuses on the magnetic exchange coupling between Co/Pt multilayers and Tb(Fe)Co films. Perpendicular spin-valves composed of Co/Pt multilayers and CoFe/TbCo bilayer were fabricated. The perpendicular GMR ratio of 4.8 % was obtained with the current-in-plane measurements. The interlayer coupling increased with increasing the net magnetization of CoFe/TbCo. A perpendicular pinning structure was proposed which possessed a high perpendicular coercivity (7 kOe) but zero net moment. Consequently, the interlayer coupling between free and pinned layers can be significantly suppressed. This perpendicular pinning structure can be potentially used for high-density perpendicular magnetic random access memory (MRAM) cells. In addition, the oscillatory perpendicular interlayer coupling field and strength as a function of Ru spacer thickness were studied for samples with the [Co/Pt]5/Co/Ru/Co/TbCo structure. For Ru thickness in the range of 0.5-1 nm, a strong antiferromagnetic (AF) coupling (J~0.38 erg/cm2) was observed. When AF coupling existed, the coercivity of Co/TbCo bilayers was enhanced because the Co/Pt multilayers stabilized the magnetization direction of Co/TbCo. Consequently, oscillatory coercivity of Co/TbCo with Ru thickness was also observed. Since the magnetization direction of the Co-sublattice in TbCo can be tuned by adjusting composition or measuring temperature, the direction of the shifted minor loop of Co/Pt multilayers can be varied accordingly while keeping the same Ru thickness. Besides, in the perpendicular interlayer coupling of the [Co/Pt]5/Co/Ru/Co/TbCo samples, the canting angles of Tb and Co moments are determined by X-ray magnetic circular dichroism. The results displayed that the interlayer exchange coupling oscillates and aligns Co and Tb moments in opposite directions. In consequence, the canting angles of the Tb and Co moments correlate with the strength of the interlayer coupling and agree with our theoretical calculations as well. The opposite alignment on the TbCo sublattice magnetizations from the interlayer coupling cannot be viewed as an effective magnetic field and thus is unique with potential applications for spintronics devices. Finally, I demonstrated the strong interfacial exchange coupling exists between Co/Pt multilayers and TbFeCo films with perpendicular magnetic anisotropy, which resulted in anomalous hysteresis loop. In addition, the interfacial exchange coupling can be increased by increasing the perpendicular magnetic anisotropy of Co/Pt multilayers or TbFeCo layer.