Magnetic and transport properties of rare-earth Au and Cu amorphous alloys

Abstract

Magnetic moment, Hall effect and resistivity of amorphous film alloys of rare earth metals with 0.4 to 0.6 atomic fraction of Au or Cu have been studied. Alloys with Nd, Gd, Dy, Tb and Ho are ferromagnetic at 4.2 °K. All but Gd have Curie temperatures below 20 °K; for Gd-Au and Gd-Cu Tc is approximately 100 °K. In addition the Gd alloys have almost full magnetization (4πM) while the remaining ferromagnetic rare earth alloys have values of 4πM only one-third to one-half of the expected saturation. Resistivities of the alloys range from 80 μΩ cm for Pr-Cu to 230 μΩ cm for Nd-Au and in general they have small negative temperature coefficients. The spontaneous Hall effect is positive for all the light rare earths with Au including Eu and negative for Gd and the remaining heavy rare earths. In the RE-Cu series the same is true except Dy through Tm have positive Hall values. The Hall Coefficient Rs for the heavy rare earths is largest for Gd where. Rs≈-0.5×10-9Ω cm/G. The sign of the Hall effect in the Au series can be attributed in part to conduction electron interactions with the spin of the rare earth atoms since the spins point in opposite directions for the light and heavy rare earths. In addition, for the heavy rare earth-Au series the tangent of the Hall angle, ρH/ρ, is proportional to the paramagnetic cursive-theta sign value of the alloy. The positive shift of ρH/ρ for the RE-Cu series may have its origin in polarization of Cu by the RE moments.