Anisotropic magnetoresistance and magnetostriction of [Fe15Ni85/Fe25Ni75] and [Co35Ni65/Fe25Ni75] multilayers

We have made a series of [AxB60−x]n multilayers and another series of [CxB60−x]n multilayers, where A=Fe15Ni85, B=Fe25Ni75, C=Co35Ni65, n=2 is the period, and xA (or xC) is the thickness of layer A (or layer C) in nanometer, respectively. The deposition temperature Ts was 340 °C. The magnetic properties, such as anisotropic magnetoresistance Δρ/ρo, saturation magnetostriction λs, and anisotropy field Hk, were measured. Although Δρ/ρo of the [C60]2 film is larger than that of the [B60]2 film, Hk 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 [A60]2 and [B60]2 films, except Hk of the former is only slightly larger. Besides, λs<0 for Fe15Ni85 alloy (the [A60]2 film), λs<0 for Co35Ni65 alloy (the [C60]2 film), and λs>0 for Fe25Ni75 alloy (the [B60]2 film). Despite these unfavorable facts, we think that if the multi-layered [AxB60−x]n or [CxB60−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 λs. 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 Ts=340 °C is the best choice for the [A/B] multilayers, when a more precise control of xA is required in order to get the linear dependence of λs on xA.