Magnetic and electric hyperfine interactions in the system Eu Sm

Magnetic and electric hyperfine interactions in the system Eu Sm were investigated with the isomeric 11/2^- state in¹⁴⁵Eu by applying the time-differential perturbed angular distribution (TDPAD) method. The temperature dependence of paramagnetism was studied between 90 K and 1000 K by measuring the magnetic hyperfine interaction frequency ω_L=g_Nμ_Nħ¹ β(T)B_ext. The paramagnetic correction factor β strictly follows the Curie-Weiss relation β=1+ C/( T-θ), with C=-50(2) K and θ=-29(5) K. This is compatible with a hyperfine field of B _int(0)=-25(1) T, a valence of two for Eu in Sm, and antiferromagnetic order at low temperatures. The temperature dependence of the electric quandrupole coupling constant v_Q, investigated between 100 K and 400 K, can be reproduced by a linear temperature variation v_Q(T)=v_Q(0) (1- AT), with v_Q(0)=16.2(4) MHz and A=7.2(8)·10^-4 K^-1. The paramagnetic relaxation time τ_rel of the nuclear alignment is proportional to the temperature of the sample, with τ_rel T^-1=3.7(2) ·10^-9s K^-1. This leads to the Korringa relation τ_J T=const=5.1(5)·10^-11s K for the relaxation time of the 4 f electronic spin J. Assuming that the relaxation of J is mainly caused by exchange interaction between conduction electrons and localized 4 f electrons at the Eu site, an exchange integral of | J _eff|=0.10(2) eV can be deduced.