Magnetic Anisotropy of V⁺⁺in CdS

Abstract

The magnetization measurements at magnetic field up to 6 Τ obtained from newly grown hexagonal Cd1-x Vx S (x 0.0004) are presented. The strong anisotropy of magnetization is observed at low temperatures (1.6 < Τ < 20 K). The data are welł described by the crystal field model calculations taking into account static trigonal Jahn-Teller distortion and spin-orbit coupling. The strong s, p-d exchange interaction is one of the most characteristic features of diluted magnetic semiconduction (DMS) [1]. DMS based on transition metal (TM) ions with less than half fllled d shell are particularly interesting for a possible ferromagnetic p-d exchange. So far, among all the studied II-VI systems, only the chromium based crystals revealed ferromagnetic p-d exchange [2] (Cr++ electronic configuration is d4). The recent growth of CdS heavily doped with vanadium calls for examining the situation in DMS with V++ ions (electronic configuration is d3).. Since the information about spin alignment is indispensable for understanding exchange interaction we thought it is worthwhile to study magnetization of this new material.The ground term of the V++ (d3 ) ion is 4F, which means that the total spin momentum of the ion is S = 3/2 and total orbital momentum is L = 3. The cubic crystal fleld splits this 7-fold orbitally degenerate term into two orbital triplets: 4 Τ1 and 4 Τ2 and an orbital singlet 4Α2 (see Fig. la). The ground orbital triplet 4 Τ1 undergoes static Jahn-Teller distortion of trigonal symmetry [3,4] yielding further splittings. Thus in the cubic symmetry there exist four equivalent possible distortion axes corresponding to one of the (111) crystal axes and four different kinds of centers are expected. In wurtzite structure, the hexagonal crystal field may be regarded as a trigonally distorted (along c axis) cubic field. In this case one of the Jahn-Teller distortion axes coincide with the hexagonal stress direction. This way the degeneracy of the four V center types is lifted. If the energy of the center •Τ1 is work was partially supported by the Committee for Scientific Research (Poland).(809)

The ferromagnetic p-d exchange interaction in Cd1-xVxS

“…Scaling of the absolute value of the magnetization allows us to evaluate the vanadium ion concentration. More detailed discussion of the magnetization is presented in [8]. The concentrations determined in this way were for all of the precipitation-free samples below x = 0.0005.…”