Motion of the magnetic moments detected by means of Mössbauer spectroscopy in magnetic systems

Abstract

The motion of magnetic moments in magnetic fihns subjected to radio-frequency radiation (R.F.R.) has been recently investigated by several authors (1-3). In the range of R.F. that they used ( (1+ 6) MHz), these authors were able to detect, by means of pick-up coils, the motion of the magnetic moments and to distinguish their full rotation from the partial rotation and from the oscillatory motion. SALANSKII and P O L S K I I , in particular, detected subarmonic oscillations that could not be explained in the frame of their experiment. In this letter we show, at our present knowledge for the first time, that the effect of R.F. fields on magnetic systems can be conveniently studied by means of Mdssbauer spectroscopy and some preliminary results are reported. I t is known that there exists a coupling between the individual atomic magnetic moments and the latt ice vibrations caused by exchange, ordinary dipole-dipole and spin-orbit interactions. These interactions depend on the interatomic spacing and the exchange of energy is thus possible betw'een the magnetic and the vibrational states. If we measure the M6ssbauer spectrum of an iron sample in a R.F. field of frequency O)RF, we expect to find, in addition to the usual six-line Zeeman-pattcrn, a set of sidebands at energies hco.~±nh~Rr,, where ~0v is the energy of the resonant ganunarays. Such sidebands are caused by the large population of the vibrational modes at (,~ = oRr, excited through the interaction with the magnetic moments. Sidebands in ~Iossbauer spectra have been produced (4) by means of ultraeustic modulation of the absorber. The R,F. used in this experiment ranges from 54 MHz to 63 MHz and the intensity of the associated nlagnetic fields, HRF, could be as large as ~ 5 G. The samples were thick iron films ((2+20) ~m thickness) and were placed parallel to the R.F. field. The