Hyperfine field of La impurity in Fe host: Experiment and theory

Abstract

The magnetic hyperfine field of La impurity in ferromagnetic Fe host has been measured by time differential perturbed angular distribution (TDPAD) technique, using the 2738 keV 23/2⁺, isomeric state in ¹³⁵La as nuclear probe, populated in the reaction $^{128}\text {Te}\left ({~}^{11}\mathrm {B}, 4\mathrm {n}\right )^{135}\!\text {La}$ at beam energy of 52 MeV. The spin rotation spectra, R(t) measured in applied field of 2 T showed Larmor precession frequency of ω_L = 93.9 ± 4.7 Mrad/sec, which corresponds to a magnetic hyperfine field, B_hf of 42.1 ± 3.3 T. From the sense of rotation observed in the R(t) spectra, the sign of the B_hf has been determined to be negative. Complimenting the experimental studies, we have performed ab-inito calculations of hyperfine field within the frame work of the density functional theory using supercell method. The calculated magnetic hyperfine field shows strong dependence with impurity concentration scaled by the supercell size. For a 2 × 2 × 2 supercell representing La concentration of 6.25 % we obtained B_hf = -21.2 T while, for a 3 × 3 × 3 supercell, corresponding to an impurity concentration of 1.8 % La, the B_hf comes out to be -48.3 T, closely agreeing with our experimental value.