Anisotropic magnetoresistance and magnetostriction of [Fe 15Ni 85/Fe 25Ni 75] and [Co 35Ni 65/Fe 25Ni 75] multilayers

Abstract

We have made a series of [A x B 60− x ] n multilayers and another series of [C x B 60− x ] n multilayers, where A=Fe 15Ni 85, B=Fe 25Ni 75, C=Co 35Ni 65, n=2 is the period, and x A (or x C) is the thickness of layer A (or layer C) in nanometer, respectively. The deposition temperature T s was 340 °C. The magnetic properties, such as anisotropic magnetoresistance Δ ρ/ ρ o, saturation magnetostriction λ s, and anisotropy field H k, were measured. Although Δ ρ/ ρ o of the [C 60] 2 film is larger than that of the [B 60] 2 film, H k of the former is also much larger. Therefore, the magnetoresistance (MR) sensitivity S, defined as the slope at the point of inflection of the MR curve, is not gained for either single-layered film. A similar situation exists between the [A 60] 2 and [B 60] 2 films, except H k of the former is only slightly larger. Besides, λ s<0 for Fe 15Ni 85 alloy (the [A 60] 2 film), λ s<0 for Co 35Ni 65 alloy (the [C 60] 2 film), and λ s>0 for Fe 25Ni 75 alloy (the [B 60] 2 film). Despite these unfavorable facts, we think that if the multi-layered [A x B 60− x ] n or [C x B 60− x ] n film could be formed, it is possible to find the optimal sample, with either the composition X A 0 or X C 0 , which exhibits good MR sensitivity S, while at the same time zero λ s. Indeed, we found that: (1) when X A 0 = 50 nm , S can be as high as 1.9%/Oe, and (2) when X C 0 = 35 nm , S is 0.40%/Oe. More importantly, we have shown that T s=340 °C is the best choice for the [A/B] multilayers, when a more precise control of x A is required in order to get the linear dependence of λ s on x A.