Temperature Dependence of Hyperfine Fields in Dysprosium Intermetallic Compounds; DyCo5, DyNi5

Abstract

The Mössbauer technique is used to investigate the temperature dependence of the effective fields acting on ${\mathrm{Dy}}^{161}$ nuclei in two intermetallic, ${\mathrm{Cu}}_5$Ca-structure-type compounds. From these measurements the temperature dependence of the dysprosium sublattice magnetization is derived. The results are compared with macroscopic magnetization measurements and with the predictions of theoretical models. In the case of Dy${\mathrm{Co}}_5$ the molecular-field model gives a very good approximation. The exchange field acting on Dy spins at 0°K is estimated to be $\frac{{\beta }_0{H}_{\mathrm{exc}}}{K}=142\mathrm{}$°K. The value of the magnetic hyperfine interaction at 4°K in Dy${\mathrm{Co}}_5$ is $g_0{\mu }_n{H}_{\mathrm{eff}}=-862\mathrm{}\pm 15$ Mc/sec and in Dy${\mathrm{Ni}}_5$ it is -790±25 Mc/sec. The value of the effective field acting on ${\mathrm{Dy}}^{161}$ nuclei in Dy${\mathrm{Ni}}_5$ corresponds to an ionic magnetic moment of 9.3±${0.3\mathrm{\mu }}_{\mathrm{B}}$. This value is higher than that obtained by magnetic measurements (${8.6\mathrm{\mu }}_{\mathrm{B}}$) and might indicate that the Ni sublattice contributes to the total magnetization by an antiferromagnetic coupling.