Modulated non-resonant microwave power absorption of FeNbO₄ powders

We report on the effects of temperature and DC magnetic field on the modulated non-resonant microwave power absorption measurements at 8.8-9.8 GHz, in powder samples of iron niobate, FeNbO₄ (FN), in the monoclinic phase (wolframite-structure). Two techniques recently implemented are used: magnetically modulated microwave absorption spectroscopy (MAMMAS) and low field non-resonant microwave absorption spectroscopy (LFNORMAS), the measurements were performed in the 90-450 K temperature range. MAMMAS response suggests that the dominant magnetic exchange is antiferromagnetic at low temperature, with a paramagnetic behavior for high temperature. The profiles obtained by plotting the slope vs. temperature of the LFNORMAS line, while cooling or heating, are similar to those detected by the MAMMAS technique, giving evidence that both types of measurement are due to the same processes of absorption. We conclude that both measurements are a manifestation of the same response to electromagnetic absorption, in which the same physical processes take place.