Abstract
The magnetization of , with from 0.025 up to 0.265, was measured at 0.6 K in a slowly varying magnetic field up to 17 T. The exchange interaction in these strongly diluted planar magnetic materials is antiferromagnetic. The in-plane cation structure is well approximated by a square lattice. The observed qualitative features, listed in the order that they appear in increasing , are as follows: a fast rise of , starting at ; a magnetization plateau (plateau of “apparent saturation”); a large magnetization step (MST), attributed to nearest-neighbor (NN) pairs; a second magnetization plateau; another large MST from NN pairs; and a third plateau that is not completed below the highest available . These features are expected from the NN cluster model presented in the preceding paper. The magnetic fields at the two MST’s give for the NN exchange constant. This value is slightly lower than reported for the undiluted member of this series, . A smaller when may be the result of an in-plane expansion with decreasing , caused by the slightly larger ion compared to . Analysis of the initial rise of at low indicates the presence of weak interactions that are not included in the NN cluster model. This conclusion is consistent with the observation (to be reported later) of a weak exchange interaction with a neighbor that is more distant than a NN. The apparent saturation value , at the first magnetization plateau, was determined for all seven samples. There is a fair agreement with the values expected from a random distribution of the Mn ions over all cation sites. The largest deviation is for samples with , where the measured is somewhat higher. In the same samples the magnetization jump at the MST’s from NN pairs is somewhat smaller than for a random Mn distribution. A proposed explanation of the discrepancies for postulates that the probability that a cation site is occupied by a is lowered by the presence of other ions at one or more NN cation sites.
- Received 3 February 2005
DOI:https://doi.org/10.1103/PhysRevB.72.064415
©2005 American Physical Society