MAGNETIZATION STEP OF ISOLATED CO2+ IONS IN HEXAGONAL CD1-XCOXS AND CD1-XCOXSE

In Cd1-xCoxS and Cd1-xCoxSe, each isolated Co2+ ion behaves as an effective spin S=3/2. The axial anisotropy results in two Kramers doublets: the lower with S(z)=+/-1/2, and the higher with S(z)=+/-3/2. In a magnetic field H along the c-axis, a level crossing at a field H(c) leads to a change of the ground state from S(z)=-1/2 to S(z)=-3/2. As a consequence, at the field H(c) a large magnetization step (MST) occurs if the temperature is sufficiently low. This MST, arising from isolated Co2+ ions in an axial anisotropy, was observed near 30 mK. A new force magnetometer operating in a plastic dilution refrigerator was used.