A study of spin density oscillations of conduction electrons in iron(1-x)-germanium(x) alloys using TDPAD technique.

摘要

The magnetic hyperfine fields H{dollar}sb{lcub}rm hf{rcub}{dollar}(x) at the non-magnetic Ge-site in an Fe-based binary alloy Fe{dollar}sb{lcub}rm 1-x{rcub}{dollar}Ge{dollar}sb{lcub}rm x{rcub}{dollar} have been measured as a function of the Ge solute concentration x for the range of 0.0 to 4.0 at.%. For the random solid solution of the alloy samples the functions H{dollar}sb{lcub}rm hf{rcub}{dollar}(x) exhibit a distribution of multiple hyperfine fields at the Ge-site. This field distribution is shown to be strongly dependent on the neighboring configuration around the Ge probe. The magnetic hyperfine fields were measured using the time-differential perturbed angular distribution (TDPAD) technique after recoil-implantation of two Ge isomers simultaneously excited by a pulsed {dollar}sp{lcub}16{rcub}{dollar}O ion beam. The objective of this measurement was to uncover the radial dependence of a net spin density of conduction electrons polarized through the s-d exchange interaction in the ferromagnetic metallic system. The selection of nonmagnetic sp-impurity {dollar}sp{lcub}67,69{rcub}{dollar}Ge isomers as probe nuclei enabled us to resolve directly the polarization of conduction electrons(CEP). The observed multiple fields at the {dollar}sp{lcub}67{rcub}{dollar}Ge nucleus, for various concentrations of the random solid solution Fe{dollar}sb{lcub}rm 1-x{rcub}{dollar}Ge{dollar}sb{lcub}rm 1-x{rcub}{dollar}, were identified as the CEP contributions transferred from the neighboring Fe moments and shown to be radially distance-dependent field components. These field components were analyzed in the 3nn approximation and found to be {dollar}Delta{dollar}H{dollar}sb1{dollar} = -8.6(18), {dollar}Delta{dollar}H{dollar}sb2{dollar} = +4.0(28) and {dollar}Delta{dollar}H{dollar}sb3{dollar} = -3.6(12) kOe, respectively corresponding to one 1nn, 2nn and 3nn Fe moment.; The deduced net spin density of conduction electrons in the present system is shown to vary both in magnitude and sign with the neighboring distance of the Fe atom. This result illustrates well the RKKY-type oscillatory behavior of CEP for its radial dependence. The extracted value of the exchange integral J(0) = +0.247(45) eV in this work confirms the strong evidence of the existence of the indirect exchange interaction in this Fe-based alloy. A more accurate g-factor of the 9/2{dollar}sp+{dollar} isomeric state in the {dollar}sp{lcub}67{rcub}{dollar}Ge nucleus was obtained as by-product: g({dollar}sp{lcub}67{rcub}{dollar}Ge) = -0.1887(26). The latest results obtained by using a long-lived {dollar}sp{lcub}69{rcub}{dollar}Ge isomer agree well with the {dollar}sp{lcub}67{rcub}{dollar}Ge results. This first-time application of the in-beam TDPAD technique to the microscopic investigation of the present problem will serve as a powerful tool in the study of solid state physics problems.