Magneto-electrodynamics at high frequencies in the antiferromagnetic and superconducting states of DyNi_2B_2C

TL;DR

This study investigates the high-frequency electromagnetic response of DyNi_2B_2C in its antiferromagnetic and superconducting states, revealing complex scattering behaviors and magnetic field effects through RF and microwave measurements.

Contribution

It provides the first detailed analysis of rf and microwave responses in DyNi_2B_2C across magnetic and superconducting transitions, highlighting novel scattering phenomena and magnetic field dependencies.

Findings

Antiferromagnetic order reduces charge carrier scattering.

RF measurements show a crossover from negative to positive magnetoresistance.

Characteristic magnetic and temperature scales related to metamagnetic transitions are identified.

Abstract

We report the observation of novel behaviour in the radio frequency (rf) and microwave response of DyNi_2B_2C 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(T,H) were measured. The establishment of antiferromagnetic order at T_N=10.3 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 conductivity relaxation 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_0H>2T and at all fields for T>15K. Several characteristic field and temperature scales associated with metamagnetic transitions (H_M1(T), H_M2(T)) and onset of spin disorder H_D(T), in addition to T_c, T_N and H_c2(T) are observed in the rf measurements.