Pressure and temperature dependence of the hyperfine fields of YFe2, YFe3and YIG

Publisher Website
Google Scholar
Abstract
The hyperfine field (HT) of 89Y in YFe2 and YFe3 and of 57Fe in single-crystal and sintered polycrystalline YIG has been measured as a function of pressure to 15 bar at room temperature and for YIG also to 7 kbar at 77K. The value of ( delta ln HT/ delta P)T for YIG at 77K is zero to experimental accuracy but is positive at room temperature due to the pressure dependence of the Neel temperature. Little difference was found between the values for single-crystal and sintered YIG. The values of ( delta ln HT/ delta P)T for 89Y in YFe2 and YFe3 were found to be in general agreement with those to be expected if the Y hyperfine field (HFF) is produced by the polarisation of s like conduction electrons but a small contribution from the d band is probably required to explain the results in detail. The spin-wave stiffness coefficient of YIG was found to be (0.568+or-0.011) eV AA2 from an analysis of the temperature dependence of the HFF below 20K. This value is in good agreement with those found less directly by earlier HFF and magnetisation measurements and confirms that there is a large discrepancy with the value found by neutron scattering experiments. The reduced HFF at the two Y sites in YFe3 was found to have the same temperature dependence below 35K (T3/2 law) and in this region decreases far more slowly than was predicted from analysis of Mossbauer measurements made up to room temperature. Above 100K the difference in the reduced HFF at the two Y sites in YFe3 appeared to be proportional to T3/2 which, in view of the low-temperature result, must arise from a partial cancellation of higher order spin-wave terms.