Abstract
The magnetic and electric hyperfine interaction of impurities on substitutional sites of cobalt metal has been investigated by γγ perturbed angular correlations (PAC) in samples prepared by melting and ion implantation of . In molten samples the saturation value of the magnetic hyperfine field of Ta is (Ta:Co(hcp); 9 K)=-40.7(6) T for hexagonal Co and ‖Ta:Co(fcc); 9 K)‖=36.3(5) T for cubic Co. In ion-implanted samples radiation damage causes a slight reduction of the hyperfine field. The magnetic hyperfine field of has also been determined in Fe: ‖Ta:Fe; 9 K)‖=61.7(9) T for a polycrystalline sample prepared by implantation. The temperature dependence of in Co has been measured between 9 and 1410 K. (T) in the hexagonal phase (T<700 K) suggests a Curie temperature for hcp Co of (hcp)=975(50) K. In the cubic phase, (T) of is close to the magnetization curve of the host with (fcc)=1398(5) K, in contrast to the anomalous temperature dependence of of most other impurities in Co investigated up to now. The electric-field gradient of on substitutional sites of hexagonal Co is ‖Ta:Co; 9 K)‖=1.23(4)× V/.
The PAC spectra reflect the transformation of the solid solution of 0.2 at. % of Hf in elemental Co into the Co-Hf intermetallic compounds and in the temperature range 900≤T≤1320 K. Upon cooling from 1400 K, elemental Co starts to transform into at about 1320 K and into at about 1220 K. At 1100 K the evolution of the phase equilibrium between the solid solution and was observed to occur with a half-life of =5.5(4) h. The temperature dependence of the hyperfine-interaction parameters suggests magnetic-ordering temperatures of 450 K and 750 K for and , respectively.
- Received 23 February 1993
DOI:https://doi.org/10.1103/PhysRevB.47.14948
©1993 American Physical Society