2018/09/07 by N. S. Sangeetha, Sangeetha, N. S., Sarah D. Cady +4
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Magnetism in coordination complexes #Rare-earth and actinide compounds #cond-mat.str-el
paper · pdf · doi:10.48550/arxiv.1809.02653
13 pages, 8 figures. The theoretical chi_D"(H) was obtained from the modified Bloch equations instead of from the Bloch equations as done previously. The temperature-dependences of the fitting parameters for the EPR spectra are therefore also different
arxiv created 2018/12/17 · arxiv updated 2018/12/18
The Eu+2 spins S = 7/2 in the metallic compound EuCo2-yAs2 order into an antiferromagnetic helical structure below a Neel temperature TN = 40 to 45 K. The effective magnetic moment mueff of the Eu spins in the paramagnetic state from 100 to 300 K is found from static magnetic susceptibility measurements to be enhanced by about 7% compared to the value expected for spectroscopic splitting factor g = 2, and the saturation moment at high applied fields H and low temperatures T is also sometimes enhanced. Here electron-paramagnetic-resonance (CW EPR) measurements versus applied magnetic field H at fixed X-band rf (microwave) angular frequency omega were carried out using a linearly-polarized rf magnetic field oriented perpendicular to H to study the microscopic magnetic properties of the Eu spins. In order to analyze the data, the complex magnetic susceptibility chi(omega) at fixed H was used that was derived for linearly-polarized rf fields from the modified Bloch equations [M. A. Garstens and J. I. Kaplan, Phys. Rev. 99, 459 (1955)] (GK). It is shown that their formulation when applied to calculate the Dysonian absorptive susceptibility chiD''(H) of local magnetic moments in metals yields a prediction that can be very different from the traditionally-used form of chiD''(H). By fitting the derivative of the field-swept CW EPR data for EuCo2-yAs2 by chiD''(H) at fixed omega derived from the GK chiD''(omega) at fixed H, the Eu spin spectroscopic splitting factor (g-factor) is found to be approximately 2.00 from 300 to ~125 K, and then to continuously increase to approximately 2.16 on further cooling to 50 K. We speculate that the enhancement of the Eu g-factor on cooling from 125 to 50 K arises from continuously-increasing local short-range ferromagnetic correlations between the Co 3d-band electrons and the Eu spins.