Spin-orbit induced noncubic charge distribution in cubic ferromagnets. I. Electric field gradient measurements on5dimpurities in Fe and Ni

Abstract

The spin-orbit induced electric field gradient at the nuclear site of 183 Os and 183 Re impurities in Fe and of 191 Pt and 186 Ir impurities in Ni was determined for ͓100͔, ͓110͔, and ͓111͔ orientations of the magnetization. The measurements were performed on single-crystal samples using nuclear magnetic resonance on oriented nuclei and modulated adiabatic fast passage on oriented nuclei. In the Ni experiments the electric field gradient was also determined for other orientations of the magnetization in the ͑110͒ plane. These data, together with previous results on the 5d impurities, provide the first fairly complete data set on the spin-orbit induced electric field gradient in cubic Fe, Co, and Ni. Our results establish in particular that the effect depends in general considerably on the direction of the magnetization. We summarize the present knowledge of these electric field gradients, their magnitude, their systematics, and the form and magnitude of their dependence on the direction of the magnetization. The properties of the effect are explained within the tight-binding model in terms of the spin-orbit induced deformation of the electron distribution. We also present and discuss data on the dependence of the hyperfine field on the direction of the magnetization, which was found to be smaller than 10 Ϫ3 , and on the inhomogeneous broadening of the electric field gradient.

Hyperfine Fields of Light Interstitial Impurities in Ni

“…Theoretical investigations on impurity systems are in general done by making use of the super-cell technique in connection with an adequate band structure method [9] or using the KKR (Korringa-Kohn-Rostoker) Green's function method to solve the corresponding Dyson equation. The later approach avoids the problem of interacting impurities in a periodic system and proved to be very powerful and flexible in the past.…”

Spin-orbit Induced Electric Field Gradients in Magnetic Solids

“…This paradox finding has been observed for the first time around 1970 by several groups (see for example [1]) who investigated Ir dissolved substitutionally in the cubic hosts bcc-Fe and fcc-Ni. Later corresponding results have been found for many other systems [9]. In addition, the anisotropy of the effect; i.e.…”

“…Interestingly, the p-contributions show a change in sign and are of the same order of magnitude as the d-contributions. In Figure 1 experimental data for F zz have been added that have been deduced from measurements on single crystal measurements with the magnetisation oriented along the [001]-axis [9]. Earlier experimental work was done in general on polycrystalline samples leading in general to smaller values for F zz .…”

Electric quadrupole interaction in cubic BCC α-Fe

“…However, the claim about the sign of the principal component was later retracted [12]. The EFG was observed for diluted 5d-impurities in cubic hosts -in particular in the α-Fe [13,14]. Calculations within spin polarized relativistic Korringa-Kohn-Rostocker (SPR-KKR) approach reproduce quite well experimental data for 5d-and 4d-impurities without resorting to the lattice relaxation [15].…”