Abstract
CeRh$_3$Si$_2$ has been reported to exhibit metamagnetic transitions below 5~K, a giant crystal field splitting, and anisotropic magnetic properties from single crystal magnetization and heat capacity measurements. Here we report results of neutron and x-ray scattering studies of the magnetic structure and crystal-field excitations to further understand the magnetism of this compound. Inelastic neutron scattering (INS) and resonant inelastic x-ray scattering (RIXS) reveal a $J_z$\,=\,1/2 groundstate for Ce when considering the crystallographic $a$ direction as quantization axis, thus explaining the anisotropy of the static susceptibility. Furthermore, we find a total splitting of 78\,meV for the $J$\,=\,5/2 multiplet. The neutron diffraction study in zero field reveals that on cooling from the paramagnetic state, the system first orders at $T_{\text{N}_1}=4.7$\,K in a longitudinal spin density wave with ordered Ce moments along the $b$-axis (i.e. the [0 1 0] crystal direction) and an incommensurate propagation vector $\textbf{k}=(0,0.43,0$). Below the lower-temperature transition $T_{\text{N}_2}=4.48$\,K, the propagation vector locks to the commensurate value $\textbf{k}=(0,0.5,0)$, with a so-called lock-in transition. Our neutron diffraction study in applied magnetic field $H\parallel b$-axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at $H=3$\,kOe, followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at $H = 7$\,kOe. This explains the nature of the steps previously reported in field-dependent magnetization measurements. A very similar behaviour is also observed for the $H\parallel$ [0 1 1] crystal direction.
Highlights
In cerium-based intermetallic compounds, the interplay between crystal-field effects, hybridization, magnetic ordering, and Kondo screening is responsible for many electronic and magnetic properties that continue to challenge our understanding
Our neutron diffraction study in applied magnetic field H b axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at H = 3 kOe, followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at H = 7 kOe
The spectra were acquired in the single photon centroiding mode and treated with the RIXSToolBox [24]; the energy step size was set to 6.2 meV, corresponding to splitting each 15 μm pixel of the Andor iKon-L CCD detector in 2.7 points, a value tuned to maximize the performance of the centroiding algorithm [25,26]
Summary
In cerium-based intermetallic compounds, the interplay between crystal-field effects, hybridization, magnetic ordering, and Kondo screening is responsible for many electronic and magnetic properties that continue to challenge our understanding. In that series is CeRh3B2, which crystallizes in a hexagonal (P6/mmm) structure characterized by chains of Ce ions along the hexagonal c axis, with extremely short intrachain distances of 3.09 Å [1] It orders ferromagnetically (with the cerium moments lying in the hexagonal plane) below TC = 115 K, a record-high Curie temperature among cerium intermetallics, but the saturation magnetic moment of 0.4μB/formula unit is strongly reduced compared to what would be expected for a Ce3+ ion in a hexagonal crystal field [2–4]. Tentative explanations of such properties have focused on unusually strong hybridization of Ce 4 f electrons with the neighboring Rh 4d or Ce 5d states [3], and/or unusually large crystal-field effect that mixes the J = 25 and J = 27 multiplets [5]. The results obtained from the present study will allow direct comparison with the existing data on CeRh3B2 (Ref. [19]) and CeIr3Si2 (Refs. [20,21])
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