Magnetization steps in Mn0.084Zn0.916F2: Exchange constant and Mn distribution - art. no. 214424

The magnetization M Of Mn0.084Zn0.916F2 was measured at 20 mK in magnetic f ields H up to 115 kOe and at 0.65 K in fields up to 175 kOe. The magnetizat ion was independent of magnetic field direction and showed no hysteresis. A fter a fast rise of M at low H, several magnetization steps (MS's) were obs erved. These MS's arose from Mn2+ pairs and triplets in which the spins are coupled by the dominant antiferromagnetic exchange constant, J(2) between next-nearest neighbors. The magnetic fields at the steps gave J(2) = -1.94 +/-0.01 K in this diluted magnetic material. The observed magnetization cur ves are in very good agreement with computer simulations which assume a ran dom Mn distribution. However, at 20 mK the widths of MS's are much larger t han expected from thermal broadening alone. Possible mechanisms for nonther mal broadening are discussed. Theoretical results for cluster statistics, f or J(2) clusters up to quintets, and for the fields at the MS's from the va rious quintet types are presented. These theoretical results also apply to nearest-neighbor (J(1)) clusters in a body-centered-cubic cation lattice.