High-field ESR study on anomalous magnetization in CsFeCl3

In CsFeCl3, an anomalous magnetization has been observed under the magnetic field exceeding 33 T applied parallel to the crystal c-axis, which cannot be explained within the framework of the fictitious spin S = 1. In order to clarify the nature of the anomalous magnetization, which is possibly due t o the ground-state crossover with the excited state S = 2, an ESR experimen t was performed under magnetic fields up to 40 T by use of a pulse magnet. The submillimeter wave around 300 GHz was supplied by Gyrotron FU IV at Res earch Center of Far Infrared Region, Fukui University. In the operation fre quency of 301 GHz absorption lines have been observed corresponding to the anomalous magnetization jump. (C) 2001 Elsevier Science B.V. All rights res erved.