RF-photon induced Mo ¨ ssbauer satellites in permalloy A. Ya. Dzyublik, a) V. Yu. Spivak, R. A. Manapov, and F. G. Vagizov Institute of Nuclear Studies, 252028 Kiev, Ukraine; Kazan Physicotechnical Institute, 420029 Kazan, Tatarstan, Russia ~Submitted 14 July 1997; resubmitted 2 December 1997! Pis’ma Zh. E ´ ksp. Teor. Fiz. 67, No. 1, 57–61 ~10 January 1998! The Mo ¨ ssbauer spectra of a permalloy film placed in an rf magnetic field are measured. The film is so thin that transverse magnetostriction oscillations are not excited in it. This permits the observation of satel- lites that are due solely to periodic variations of the magnetic field at the nucleus. The data are in good agreement with calculations per- formed in the model of step-wise field reversals. On application of an additional static magnetic field the splitting of the satellites is observed, as predicted by the model of asymmetric step-wise field reversals. © 1998 American Institute of Physics. @S0021-3640~98!01101-3# PACS numbers: 76.80.1y, 75.80.1q Many Mo ¨ ssbauer experiments ~see the reviews 1–4 ! are devoted to the investigation of soft ferromagnets in a radio-frequency ~rf! magnetic field with angular frequency V . Equidistant ~separated by an interval V ) satellites, which are split if the quadrupole interaction is also strong, were observed in these experiments. At high frequencies V these spectra collapse into a single line or doublet. The main idea forming the basis of the model of step-wise field reversals is that the magnetic field h( t ) at a nucleus in a soft ferromagnet placed in an rf field H rf ( t ) jumps periodically between two values 1h 0 and 2h 0 . The corresponding equations for the absorption cross section are derived in Refs. 5–7. The reversals can be simply explained as follows ~see also Ref. 8!. It is known 9,10 that soft ferromagnets have a cluster structure. Such weakly interacting clusters behave similarly to superparamagnetic particles in which all spins are strongly coupled. The magnetization M c of a cluster can be oriented along the easy-magnetization axis or in the opposite direction. Correspondingly, the potential energy W 0 ( w ) of a cluster as a function of the angle between M c and the easy-magnetization axis has two minima. In a field H rf ( t ) a cluster acquires the additional potential energy V ( t ) 52M c • H rf ( t ). Then the total potential energy W 0 1V ( t ) will be a periodic function of time. Its oscillations force M c to undergo periodic jumps between two opposite potential wells with a time interval T /2 between successive jumps, where T 52 p / V is the period of the rf field. Application of an additional static magnetic field H 0 gives another static contribution 2M c • H 0 to the potential energy. This makes one potential well deeper than the other, even in the absence of H rf ( t ). The applied field H rf ( t ) with amplitude greater than H 0 will once again give rise to jumps of the magnetization but in this case the time T 1 which a cluster spends in the potential well with magnetization M c parallel to H 0 will be greater than the time T 2 spent in a well with M c antiparallel to H 0 . A nucleus interacting with a reversing field 61 61 0021-3640/98/010061-06$15.00 © 1998 American Institute of Physics