Nuclear magnetic resonance study of polycrystalline Sr1-xCaxRuO3 (0 x1.0)

Abstract

A zero-field spin-echo nuclear magnetic resonance (NMR) study of 99,101Ru nuclei in polycrystalline powder samples of magnetically ordered Sr1 - xCaxRuO3 (0 x1.0) is reported. The NMR spectrum for SrRuO3 at 1.3 K consists of two peaks at 64.4 MHz and 72.2 MHz corresponding to the 99Ru and 101Ru isotopes, respectively, and a hyperfine field of 329 kG. With the replacement of Sr by Ca, the peaks broaden somewhat, although there is essentially no change in the peak frequencies. However, the two resonance peaks show a significant reduction in height with intensity being shifted into the wings. Although electric quadrupole effects are present, the results suggest that the reduction of peak intensity when Ca is added is due mainly to a progressive loss of Ru moments participating in the magnetic ordering. The loss is a consequence of the dilution of the ferromagnetic exchange coupling between the moments. A measure of the spontaneous magnetization temperature dependence for SrRuO3 (21 K) has been obtained from the shift of the peak frequencies. It was found that the spontaneous magnetization decreases with a Bloch law T 3/2 temperature dependence characteristic of spin-wave excitations. From the coefficient of the temperature dependence, a value of 2.4 meV was obtained for the exchange integral which is consistent with the observed ordering temperature.