A remarkable transformation of magnetic resonance spectra as a result of a mutualinfluence of coexisting para- and ferromagnetic phases

Abstract

In this work, we carry out the analysis of the resonance absorption of electromagneticradiation for the system in which para- and ferromagnetic phases coexist over a widetemperature region. It is found that taking account of the mutual influence ofcoexisting phases gives rise to the appearance of substantial changes in the curves ofresonance absorption and values of resonance fields, as well as to making thegeometry of a phase distribution dependent on an external magnetic field. Nearthe temperature boundaries of the phase coexistence region, the expressions fordescription of the curves of the dispersive absorption of electromagnetic radiation areobtained and the rules of the behaviour of the resonance fields for each of thephases are specified. As follows from the calculations, the resonance field for theparamagnetic phase becomes dependent on the shape of the sample, the saturationmagnetization and the fraction of ferromagnetic phase. It is shown that the character ofmagnetic resonance spectra and the features of their temperature change agree wellwith the experimental data, obtained by various groups of researchers on thesingle crystalline and polycrystalline samples of doped perovskite manganites.