Structures with improved magnetic characteristics for giant magnetoresistance applications

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Abstract
Giant magnetoresistance (GMR) structures of various thicknesses with layers of different commonly used fcc NiCoFe alloys and Cu layers were made and several approaches aimed at improving their magnetic properties were investigated. Atomic force microscopy was used to observe roughness and grain size; x-ray diffraction indicated crystalline orientation. Vibrating sample magnetometry was the principal method used to observe the magnetic characteristics. Roughness increased for thicker layers, but in itself did not strongly degrade magnetic switching. Grain size also increased with thickness and was found to correlate strongly with poor switching for Co rich alloys. Because these alloys have large magnetocrystalline anisotropy, larger grains apparently act more independently, leading to increased coercivity and slow saturation. Strategies were implemented that achieved small grain size even in thick structures and therefore resulted in abrupt switching in low fields and in higher remanent magnetization. Thin Fe, Cr and especially Ta interlayers were found to be effective in suppressing grain growth and maintaining [111] texture. This significantly improved the switching for structures containing significant amounts of Co. Even for rough GMR structures with >100 nm thickness the coercivity could be reduced by roughly an order of magnitude by use of 0.5 nm Ta interlayers.