Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility

Abstract

The authors have measured the nuclear specific heat C{sub n} and nuclear susceptibility {Chi}{sub n} of In nuclei (I=9/2, {mu}=5.5 {mu}{sub n}) in the cubic intermetallic compound AuIn{sub 2} (Korringa constant {kappa}=0.11 Ksec) in the normal conducting state at 30 {mu}K {le} T {le} 10 mK and 2mT {le} B {le} 115 mT. Their data show a positive nuclear Weiss temperature {theta} = +43 {mu}K and that the In nuclei undergo a nuclear ferromagnetic transition at T{sub c} = 35 {mu}K. The In nuclei experience an internal field of about 10mT (obtained from C{sub n} at T > T{sub c}). The nuclear ordering temperature T{sub c} and the internal field increase with applied magnetic field. From the data the authors deduce exchange constants for the investigated system. The critical entropy reduction {delta}S(T{sub c})/S{sub max} = 8.6% and critical enthalpy {delta}E = 0.28 RT{sub c} are in reasonable agreement with the measured ordering temperature T{sub c}, applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time {tau} calculated from the real and imaginary parts of {Chi}{sub n} is 10 msec at T>50 {mu}K, but drops to {tau}<1 msec at T{sub c}. This is the firstmore » observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T{sub nuclear} = T{sub electron}.« less