Anisotropic magnetoresistance and electrical resistivity of Co 1- δNi 3+ δ. I. Single-crystal samples
Three cylindrical single crystals of CoNi 3 alloy, one having <1 0 0> axis, another <1 1 0> axis, and the last <1 1 1> axis, were taken to measure the changes of resistivity either in a longitudinal or transverse magnetic field at temperatures T=77, 90, and 300 K, respectively. The Döring expression with coefficients from k1 to k5 was used to fit the experimental data. In addition, these crystals have been processed with different thermal treatments, including anneal and quench. We find in all cases k1>0, k2>0, k1⩾ k2, k3⩽0, k4⩽0, and k5>0. From the temperature dependence of | k1|,| k2|, and | k4|, there is a maximum for each of them near T=90 K. Having obtained k1- k5, it is possible to calculate the `ideal' (i.e. free from the texturing and/or grain-boundary effect) anisotropic magnetoresistance ∆ ρ/ ρ0 for randomly oriented polycrystalline Co 25Ni 75. We find that different thermal treatments may result in different values for ∆ ρ/ ρ0 (calculated) and ρ0. A further discussion will be presented in Part II.