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 Eu¹⁵¹ and Eu¹⁵³ 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 J₁ and second-neighbor exchange J₂, as well as an effective field H which simultaneously produced reasonable agreement between calculation and experiment are J₁=0.20±0.01^∘{}K, J₂=-0.08∓0.02^∘{}K and H=4.0±0.2 kOe. These values are fairly consistent with other parameters known for EuS.