MAGNETIZATION STEPS OF NEAREST-NEIGHBOR EXCHANGE INTERACTIONS IN CDS(CO) AND CDSE(CO) IN FIELDS TO 60 TESLA

The first of three expected magnetization steps (MSTs), due to the nea rest-neighbor (NN) antiferromagnetic exchange J(1) between Co2+ pairs in CdS(Co) and CdSe(Co), is observed by differential magnetization mea surements in pulsed magnetic fields up to 60 T. In contrast with earli er results on CdS(Mn) which showed MSTs in pulsed fields much narrower by thermal broadening, the MSTs of the Co substituted materials are m uch broader, extending from about 35 to 55 T. The broad CdS(Co) MST sh ows structure due to the two inequivalent NN sites in the wurtzite str ucture. For Cd1-xCoxS, an average J(1)/k(B) = -30.6 +/- 1.7 K is obser ved for a single crystal with x = 0.036 and -32.1 +/- 1.7 K for a mult icrystal with x = 0.064. For multicrystalline Cd1-xCoxSe with x = 0.04 6, the broad MST has a maximum corresponding to J(1)/k(B) = - 31.0 +/- 2 K. The effects of more-distant neighbors and crystalline fields are discussed.