Am. Mulders et al., PRRU2SI2 - A GIANT ANISOTROPIC INDUCED MAGNET WITH A SINGLET CRYSTAL-FIELD GROUND-STATE, Physical review. B, Condensed matter, 56(14), 1997, pp. 8752-8759
The magnetic properties of PrRu2Si2 have been investigated experimenta
lly by specific heat, single-crystal magnetization, Pr-141 Mossbauer a
nd muon spectroscopies, neutron powder diffraction, and inelastic neut
ron scattering, leading to the determination of its zero-field phase d
iagram and its crystal electric-field energy levels below 40 meV. PrRu
2Si2 undergoes a magnetic phase transition at T-N similar or equal to
16 K to an axial incommensurate sine-wave magnetic structure character
ized by a wave vector tau = (0.133, 0.133, 0), followed by a first-ord
er phase transition at T-C similar or equal to 14.0 K to an axial ferr
omagnetic structure. The lowest crystal electric-field states are the
two singlets \Gamma(t1)((1))] and \Gamma(t2)] separated by 2.25 meV. T
he low-temperature properties are described by a Hamiltonian identical
to that of an Ising system with a transverse magnetic field. Since th
e ratio of the exchange energy to the energy splitting between the sin
glets is sufficiently large, it exhibits spontaneous magnetization. Th
e nature of the two singlet states explains the giant magnetic anisotr
opy. The random-phase approximation predicts the value of the high-fie
ld magnetization but yields a low-field magnetization too small by sim
ilar to 15%. Possible application of our results to uranium intermetal
lic compounds is painted out.