| Magnetization-step (MST) spectroscopy is applied and extended to address several problems in the areas of dilute magnetic semiconductors (DMS) and molecular magnetism. Exchange interactions in Pb{dollar}sb{lcub}rm 1-x{rcub}{dollar}Eu{dollar}sb{lcub}rm x{rcub}{dollar}S and in (Fe (Salen) Cl) {dollar}sb2{dollar} are determined with this technique.; Magnetization steps (MSTs), arising from quartets consisting of four identical spins, are studied for the first time. Each of the six possible types of quartets gives rise to MSTs at low temperatures. Analytical expressions (when possible) and numerical solutions for the magnetic fields at the MSTs are obtained. Magnetization measurements in Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}S, and Zn{dollar}sb{lcub}rm 1-x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Se, performed at 0.6 K, reveal the first step from the quartets. The location and size of this MST are close to the predicted values.; Exchange and anisotropy interactions in the DMS Pb{dollar}sb{lcub}1-x{rcub}{dollar}Eu{dollar}sb{lcub}rm x{rcub}{dollar}S are studied. Magnetization measurements at 0.6 K reveal rounded ramps from Eu{dollar}sp{lcub}2+{rcub}{dollar} pairs. Computer simulations of the observed ramps identify the dominant AF exchange constant J as the nearest-neighbor (NN) exchange constant {dollar}Jsb1{dollar}, and also show that the distribution of the Eu{dollar}sp{lcub}2+{rcub}{dollar} ions in Pb{dollar}sb{lcub}rm 1-x{rcub}{dollar}Eu{dollar}sb{lcub}rm x{rcub}{dollar}S is random. Analysis of MSTs observed in Sao Paulo at 20 mK gives the precise value of {dollar}Jsb1.{dollar} An observed splitting of the MSTs at 20 mK is simulated by using exchange anisotropy.; The exchange constant J = {dollar}-{dollar}8.4 {dollar}pm{dollar} 0.2 cm{dollar}sp{lcub}-1{rcub}{dollar} for Fe{dollar}sp{lcub}3+{rcub}{dollar} dimers in (Fe (Salen) Cl) {dollar}sb2{dollar} is obtained by analyzing pulsed-field magnetization data obtained at MIT. Computer simulations reproduce the strong magnetocaloric effects observed in these experiments. The line shapes of the MSTs indicate the presence of unidentified weak interactions besides the intra-dimer isotropic exchange. Traditional susceptibility data give {dollar}J cong -8{dollar} cm{dollar}sp{lcub}-1{rcub}.{dollar}... |
