Thermal Stability of Synthetic Antiferromagnet and Hard Magnet Coupled Spin Valves
The magnetic properties of current-in-plane (CIP) giant magnetoresistive (GMR) spin valves employing synthetic antiferromagnet (SAF) pinning have been investigated. The conventional spin valve structure, with a ferromagnetic (FM) layer pinned by an antiferromagnet (AFM) layer, exhibits high electrical resistance, the AFM typically being a high resistivity material. We have investigated pinning with a Co/Ru/Co SAF trilayer only, with no additional AFM pinning. We have also investigated spin valves employing a hard magnet layer in three different configurations as the pinning/pinned layer. Elimination of the AFM-induced parasitic resistance has the potential for yielding a higher GMR ratio in current-perpendicular-to-the-plane (CPP) structures. The full-film properties have been optimized by using vibrating sample magnetometry and CIP magnetotransport measurements. The thermal stability of SAF-pinned spin valves and hard magnet-pinned spin valves has been characterized through magnetotransport measurements of up to 400 K, and found to have measurable MR even at that temperature. A study of the M-H loops for the SAF spin valve showed no change up to 500 K. Therefore, these non-AFM-containing spin valves appear to be usable in CPP devices under practical head operating temperatures, representing a significant advance in reduced stack resistance, increased MR ratio, and reduced coupling between free and pinned layers in a small-dimensional patterned structure.