ИСТИНА

In this work we report on the studies of interaction of millimetre wave radiation with hard magnetic materials exhibiting giant coercivity. Utilizing methods of continuous wave monochromatic and pulse time-domain spectroscopies, the terahertz-subterahertz (90-1100 GHz) electrodynamics of epsilon iron oxide, ε-Fe2O3, and cobalt ferrite, CoFe2O4, was investigated. We trace the temperature evolution (T = 5-300 K) of the detected natural (zero external magnetic field) resonance (NFMR) lines and study variation of their parameters due to form of the material (ceramics or powder in polymer matrix) and purity of the phase. The fingerprints of phase transitions are found in both compounds under study. NFMR line in CoFe2O4:α-Fe2O3demonstrate a significant blue-shift with cooling and then splits in two separate components at temperatures below 80 K (Fig. 1). In ε-Fe2O3, the NFMR line shows the opposite dynamics and red shifts towards low temperatures. The redshift of the NFMR line in ε-Fe2O3 could be attributed to the weakening of the magnetocrystalline anisotropy constant, as discussed in [1]. At temperatures below 140 K, the NFMR disappears which could be associated with a change in magnetic ordering in ε-Fe2O3, as claimed in [1]. Acknowledgements: This work was supported by RSF, grant 21-79-10184. [1] Gich, M., et al., Journal of Applied Physics 98.4, 044307 (2005).