PrRu2Si2: A giant anisotropic induced magnet with a singlet crystal-field ground state

Abstract

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.

Magnetic field and temperature dependence of the amplitude-modulated magnetic structure ofPrNi2Si2determined by single-crystal neutron diffraction

“…21 A joint analysis of specific heat, magnetization, magnetic susceptibility, and inelastic neutron-scattering measurements suggests a singlet crystal-field ground state 12,13…”

Crystal-Field Origin of the Giant Magnetocrystalline Anisotropy of PrRu2Si2

“…In conclusion, we have shown that the giant anisotropy field as large as 400 T observed in PrRu2Si2 [1,2] can be accounted for by crystal-field interactions. We are quite convinced in our crystal-field explanation for this giant magnetocrystalline anisotropy as it provides also a quite consistent description of other magnetic and electronic properties, like temperature dependence of the paramagnetic susceptibility and of the heat capacity.…”

“…PrRu2Si2 exhibits a giant magnetocrystalline anisotropy about 400 T [1,2]. The aim of this contribution is to find the origin of this giant anisotropy, in the current literature as the source of the anisotropy three main factors are mostly discussed [1]: the anisotropic exchange, the hybridization, and the single-ion mechanism.…”

“…It crystallizes in a tetragonal structure of ThCr2Si2-type and exhibits the ferromagnetic ordering below 14K [1,2,5,6]. The magnetization curves measured on a single-crystalline sample [1], which reveal this giant magnetocrystalline anisotropy, are shown by experimental points in In order to understand the magnetic properties of PrRu2Si2 we have applied the individualized-electron model for rare-earth compounds [7,8].…”

Pr-magnetism in the quasi-skutterudite compound PrFe2Al8

“…Induced moment magnetic ordering in this compound would require very high internal exchange energy to achieve ordering. In some other Pr-based compounds like PrRu 2 Si 2 and PrNi 2 Si 2 , relatively smaller crystal field separations are (of 2.25 meV and 3.3 meV, respectively) [26,27]. In the present case of PrFe 2 Al 8 the knowledge of the first excited crystal field level first originated from a simulation of the Schottky specific heat, which predicts the first level at around 10 K. An estimation of the exchange constant is in general possible through the relation, θ p = JexJ(J+1) 3kB where θ p is the Curie-Weiss temperature and J ex is the exchange constant.…”