Magnetoelectrodynamics at high frequencies in the antiferromagnetic and superconducting states ofDyNi2B2C

Abstract

We report the observation of novel behaviour in the radio frequency (rf ) and microwave response of DyNi2B2C 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 Zs = Rs + iXs was measured which yields the T dependence of the complex conductivity σ1 − iσ2 in the SC and AFM states. At radio frequencies (4 MHz), the H and T dependence of the penetration depth λ(T, H) were measured.The establishment of antiferromagnetic order at TN = 10.3 K results in a marked decrease in the scattering of charge carriers, leading to sharp decreases in Rs and Xs. However, Rs and Xs 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 TN . Anomalous decrease of scattering at moderate applied fields is observed at temperatures near and above TN , 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 µ0H > 2T and at all fields for T > 15K. Several characteristic field and temperature scales associated with metamagnetic transitions (HM1(T ), HM2(T )) and onset of spin disorder HD(T ), in addition to Tc, TN and Hc2(T ) are observed in the rf measurements.74.25. Ha, 74.25.Nf, 74.72.Ny, 75.20.Hr, 75.40.Gb, 75.50.Ee, 75.90.+w

Recent developments in the characterization of superconducting films by microwaves

“…Similarly, studies of microwave dissipation and relaxation in magnetic or dielectric materials have received great attention recently, e.g., to resolve the coupling of spins and charges in magnetic superconductors like the borocarbides or rutheno-cuprates [6,7,8], or materials displaying colossal magneto-resistance [9], or to search for low-loss ferrite or ferroelectric materials for frequency-agile devices [10,11,12]. …”

Radio-frequency impedance measurements using a tunnel-diode oscillator technique

“…Tunnel-diode oscillators (TDO) which essentially operate based on the principle outlined above, have been used in the past to study a variety of issues ranging from paramagnetic susceptibility in salts to penetration depth in superconductors [1][2][3][4]. Over the past few years, the Northeastern University group has demonstrated the success of using this method to investigate phenomena in new materials like cuprate superconductors [5], borocarbide superconductors [6] and more recently, manganites exhibiting colossal magneto-resistance (CMR) effects [7].…”

“…Over the past few years, the Northeastern University group has demonstrated the success of using this method to investigate phenomena in new materials like cuprate superconductors [5], borocarbide superconductors [6] and more recently, manganites exhibiting colossal magneto-resistance (CMR) effects [7].…”