Abstract
The spin wave excitations of an 153EuS single crystalline sample have been measured by inelastic neutron scattering through the entire 1. Brillouin zone with the momentum Q parallel to the main symmetry directions 〈100〉, 〈110〉, and 〈111〉, and for temperatures ranging from well below (1.3 K) to well above (36 K) the Curie temperature (Tc = 16.6 K). Least square fits of the low-temperature spin wave dispersion curves to the Holstein-Primakoff theory yielded the exchange energy constants Jr of the Heisenberg operator up to the fifth (r = 5) Eu-Eu-neighbour interactions as follows: J1/kB = 0.22(1±3)K, J2/kB = −0.10(0±4)K, J3/kB = 0.00(6±2)K, J4/kB = −0.00(7±2)K, and J5/kB = −0.00(4±2)K. They correspond with Θp = 21.1±0.2 K and also with the theoretically expected ratio of Tc/Θp. The temperature dependence of the spin wave energies, which has been measured for large-q spin-waves up to T/Tc = 1.5, does not agree with the spin-wave renormalization theory. This EuS-result differs from EuO, where the spin-wave renormalization was reported to agree with theory. The variation of the Jr with magnetic dilution is discussed by considering related results on the EuxSr1−xS system.
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