The magnetic properties of PrRu 2 Si 2 have been investigated experimentally by specific heat, single-crystal magnetization, 141 Pr Mössbauer and muon spectroscopies, neutron powder diffraction, and inelastic neutron scattering, leading to the determination of its zero-field phase diagram and its crystal electric-field energy levels below 40 meV. PrRu 2 Si 2 undergoes a magnetic phase transition at T N Ӎ 16 K to an axial incommensurate sine-wave magnetic structure characterized by a wave vector ϭ ͑0.133, 0.133, 0͒, followed by a first-order phase transition at T C Ӎ 14.0 K to an axial ferromagnetic structure. The lowest crystal electric-field states are the two singlets ͉⌫ t1(1) ͘ and ͉⌫ t2 ͘ separated by 2.25 meV. The low-temperature properties are described by a Hamiltonian identical to that of an Ising system with a transverse magnetic field. Since the ratio of the exchange energy to the energy splitting between the singlets is sufficiently large, it exhibits spontaneous magnetization. The nature of the two singlet states explains the giant magnetic anisotropy. The random-phase approximation predicts the value of the high-field magnetization but yields a low-field magnetization too small by ϳ 15%. Possible application of our results to uranium intermetallic compounds is pointed out.

Spin dynamics in RENi5 ferromagnets by microSR measurementsGubbens, P.C.M.; Moolenaar, A.A.; de Reotier, P.D.; Yaouanc, A.; Kayzel, F.; Franse, J.J.M.; Prokes, K.; Snel, C.E.; Bonville, P.; Hodges, J.A.; Imbert, P.; Pari, P.

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