Spin excitations and new orientational transition in a holmium orthoferrite with magnetic vacancies: HoFe1-xAlxO3
Mukhin A. A., Fedorov I. V., Egoyan A. E., Lebedev S. P., Kozlov G. V., Prokhorov A. S., Balbashov A. M., Parsegov I. Yu.
Dynamic properties of holmium orthoferrite are strongly influenced by low concentrations of nonmagnetic Al3+ dopant ions (magnetic vacancies). Anomalies are observed on the temperature dependence of two antiferromagnetic-resonance modes in the submillimeter spectra of HoFei _XA1X03. These anomalies (a discontinuity and slope changes in the frequencies) point to a spin-flip transition at Τ= 60 К from a weakly ferromagnetic Г4 state to an antiferromagnetic Г] state, induced by magnetic vacancies. A model is offered to explain the observations. The exchange field of the magnetic vacancies is determined.