Magnetoelectrodynamics at high frequencies in the antiferromagnetic and superconducting states ofDyNi2B2C

We report our observation of the behavior of the radio frequency (rf) and microwave response of ${\mathrm{DyNi}}_2{\mathrm{B}}_2\mathrm{C}$ over a wide range of temperature (T) and magnetic field (H) in the antiferromagnetic (AFM) and superconducting (SC) states. At microwave frequencies of 10 GHz, the T dependence of the surface impedance $Z_s{=R}_s{+iX}_s$ was measured which yields the T dependence of the complex conductivity ${\sigma }_1-i{\sigma }_2$ in the SC and AFM states. At radio frequencies (4 MHz), the H and T dependence of the penetration depth $\lambda \mathrm{}(T,H)\mathrm{}$ were measured. The establishment of antiferromagnetic order at $T_N=10.3\mathrm{}\mathrm{K}$ results in a marked decrease in the scattering of charge carriers, leading to sharp decreases in $R_s$ and $X_s.$ However, $R_s$ and $X_s$ differ from each other in the AFM state. We show that the results are consistent with relaxation processes whence the scattering rate becomes comparable to the microwave frequency. The rf measurements yield a rich dependence of the scattering on the magnetic field near and below $T_N.$ Anomalous decrease of scattering at moderate applied fields is observed at temperatures near and above $T_N,$ and arises due to a crossover from a negative magnetoresistance state, possibly associated with a loss of spin disorder scattering at low fields, to a positive magnetoresistance state associated with the metallic nature. The normal state magnetoresistance is positive at all temperatures for ${\mu }_{0}H>\mathrm{}2\mathrm{}\mathrm{T}$ and at all fields for $T>\mathrm{}15\mathrm{}\mathrm{K}.$ Several characteristic field scales associated with metamagnetic transitions $\left[H_{M1\mathrm{}}{\mathrm{}\left(T\right),H}_{M2\mathrm{}}\mathrm{}\right(T\left)\mathrm{}\right],$ the onset of spin disorder $H_D\mathrm{}\left(T\right)\mathrm{}$ and the upper critical field $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ are observed in the rf measurements.