ESR measurements on CoNiO powders

Powders of cobalt core with a nickel(II) oxide shell (CoNiO) have been studied by Electron Spin Resonance (ESR) technique in the temperature range of 10-300 K. A strong and broad (1300 G) single ESR peak in X, K, and Q-band spectra has been observed at all measurement temperatures. While the g-value remains almost constant, both the ESR linewidth and the intensity were first seen to increase slowly down to Tc= 155 K and then smoothly decrease down to 10 K. This is attributed to a typical spin-glass behavior. Some small and relatively smooth changes at about 60 K, 90 K, 210 K, and 250 K are appeared as well. A linear dependence of resonance field on microwave frequency is observed. The effective g-value and internal field are calculated from the experimental results by using a model and deduced as 2.1014 and 90 G, respectively