MAGNETIZATION STEPS IN PB1-XEUXS - EXCHANGE AND ANISOTROPIC INTERACTIONS

Magnetization measurements were performed on five Pb1-xEuxS samples, w ith 0.0092 less than or equal to x less than or equal to 0.059. Two of the samples were measured at 20 mK in magnetic fields H up to 50 kOe parallel to the [111] and [100] directions. The other three samples we re measured at 0.6 K in fields up to 180 kOe. The 20 mK data exhibit m agnetization steps (MST's) arising from pairs. These MST's depend on t he direction of H, so that anisotropic interactions must be included i n the data analysis. The MST's lead to a value J/k(B) = -0.228 +/- 0.0 07 K for the dominant antiferromagnetic exchange constant. Computer si mulations identify this J as the nearest-neighbor exchange constant J( 1), and show that the Eu distribution over the cation sites is random or very nearly random. The MST's from pairs exhibit a splitting when H is parallel to [100]. The splitting is tentatively attributed to exch ange anisotropy, in which case the above value for J refers to the ave rage exchange constant J, The 20 mK data for H parallel to[100] also s how a MST from isolated Eu ions. This MST occurs because such ''single s'' are subjected to a cubic crystal-field anisotropy.