Differential magnetic susceptibility and microwave resonance in a quasi-Ising magnet at high magnetic fields

Magnetization and magnetic resonance have been measured in pulsed magnetic fields at low temperatures on a Dy0.3Y2.7Fe5O12 single crystal. The magneti zation and the differential magnetic susceptibility have been measured in t he range T = 4.2-200 K in the fields up to 50T, oriented along the [100] ax is. Magnetic reversal of the rare-earth magnetic subsystem is revealed by s ets of several jumps of the magnetization in the range 5-40 T at temperatur es below 40 K. A good quantitative description of the static magnetic prope rties of the crystals is obtained in the framework of a model of the quasi- Ising ordering of Dy3+ ions. Microwave absorption at frequencies from 37 to 85 GHz was studied for this crystal in pulsed magnetic field up to 30 T at T = 4.2 K and H\\[100]. At the fields corresponding to the phase transitio ns, several soft modes are observed, but additional soft modes of magnetic resonance are observed far away from the transition fields. This indicates the existence of metastable states of Dy0.3Y2.7Fe5O12 samples below and abo ve the exchange field H-ex = 21 T. A qualitative description of the observe d phenomena is presented, based on the assumption of the magnetic analogue of the Jahn-Teller effect. (C) 2001 Elsevier Science B.V. All rights reserv ed.