| Popis: |
Previous measurements of the low-frequency branch of the "easy-plane" antiferromagnet have been extended to the high-frequency branch. The resonance fields as a function of angle at constant frequencies greater and less than the zero-field resonance frequency, ${\ensuremath{\omega}}_{c}$, have been measured and analyzed based on resonance equations including the dipolar and a phenomenological uniaxial anisotropy energy. Good agreement is obtained for branches associated with the different $T$ domains. Deviations, attributed to domain-wall effects, are observed. The zero-field resonance frequency, ${\ensuremath{\omega}}_{c}$, has been determined from measurements of $\ensuremath{\omega}$ vs $H$ with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ in an easy plane. The decrease in ${\ensuremath{\omega}}_{c}(T)$ with increasing temperature is proportional to ${T}^{\frac{3}{2}}$ and is the same as found for the critical (exchange) field by Oliveira et al. The frequency ${\ensuremath{\omega}}_{c}$ at $T=0$ corrected for demagnetizing effects corresponds to a dipolar interaction, ${K}_{d}=0.817\ifmmode\times\else\texttimes\fi{}{10}^{6}$ erg/${\mathrm{cm}}^{3}$, which is \ensuremath{\sim}10% larger than the classically calculated value for EuTe. The exchange field, ${H}_{E}$, determined from the variation $\ensuremath{\omega}$ vs $H$ with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ in an easy plane was obtained. The value at $T=0$ and corrected for demagnetizing effects is ${H}_{E}(0)=73.0$ kOe compared with the value ${H}_{E}=72.2$ kOe determined directly by Oliveira et al. This excellent agreement is considered fortuitous. |
