Application of Spin-Wave Theory to EuS

Magnetization data for EuS powder in zero field and at liquid-helium temperatures has been obtained by nuclear magnetic resonance of both the ${\mathrm{Eu}}^{151}$ and ${\mathrm{Eu}}^{153}$ nuclei. These data are considered simultaneously with those for the specific heat of EuS powder obtained by McCollum and Callaway in order to provide a more definitive application of the spin-wave theory to this material. The theory is that given by Holstein and Primakoff and special attention is given to the effects of magnetic dipolar coupling on the spin-wave energy and moment. The calculation was carried out by summation over the exact Brillouin zone. Values of the nearest-neighbor exchange interaction $J_1$ and second-neighbor exchange $J_2$, as well as an effective field $H$ which simultaneously produced reasonable agreement between calculation and experiment are $J_1=0.20\mathrm{}\pm 0.01$°K, $J_2=-0.08\mathrm{}\mp 0.02$°K and $H=4.0\mathrm{}\pm 0.2$ kOe. These values are fairly consistent with other parameters known for EuS.