Ligand Mediated Magnetoelectronic Coupling Across Metamagnetic Transitions in CrPS4

Abstract

Chromium thiophosphate is a long-known material: a layered semiconducting antiferromagnet. Its recently discovered gate-tunable metamagnetic phase transitions, the remarkable positive and oscillating magnetoresistance as a tunnel barrier, and its Fano-resonance luminescence, elusive among the multitude of Cr3+ compounds, call for revisiting the understanding of its electronic structure, especially regarding how it relates to magnetic order. Here, we employ X-ray magnetic circular dichroism, implemented in both absorption and resonant inelastic X-ray spectroscopies, together with quantum many-body calculations, to unveil the complex nature of magnetoelectronic coupling in CrPS4, featuring hybridization between crystal-field and charge-transfer transitions. We reveal the role of extended superexchange paths involving P and S atoms, mediating interactions between the Cr spins across the different magnetic phases: antiferromagnetic, canted, and ferromagnetic. Our results elucidate the electronic states involved in these phases and provide prescriptions for engineering the metamagnetic phase diagram of CrPS4.

Figures (6)

• Figure 1: Metamagnetic phases of CrPS$_4$. (a) Side and top views of the crystal structure of CrPS$_4$, in which Cr atoms are octahedrally coordinated by S atoms. (b) Magnetic phase diagram of CrPS$_4$ (out of plane $\mu_0 H$ vs. $T$) reconstructed from magnetometry measurements. (c) Crystal-field splitting of Cr$^{3+}$ 3d states in octahedral ($O_h$) and trigonal-distorted ($O_h + D_{3d}$) cluster geometry, with the corresponding high-spin configuration.
• Figure 2: Magnetic response of CrPS$_4$ across the metamagnetic transition via XMCD. (a) Cr $L_{3,2}$-edge XAS spectrum of CrPS$_4$ at 5 K, overlaid with a reference Cr$_2$O$_3$ spectrum, emphasizing absolute energy positions and the chemical shift. (b) XMCD spectrum of CrPS$_4$ at 5 K under a 9 T magnetic field (NI geometry), normalized to the maximum XAS amplitude. The XMCD is obtained as the difference between XAS spectra recorded with opposite photon helicities. (c) SQUID magnetometry at 5 K and 20 K for out-of-plane fields, with vertical lines indicating the spin-flop transition. (d) Cr$^{3+}$ element-specific magnetization at 5 K (NI geometry), extracted from the XMCD intensity at peak A (576.2 eV). Error bars correspond to the residual field-independent contribution.
• Figure 3: Ligand effects in CrPS$_4$. (a, b) Field-dependent XMCD at the Cr $L_3$ edge of CrPS$_4$ (5 K) across the spin-flop transition ($\mu_0 H_{\mathrm{flop}} \approx 0.9$ T at 5 K for $\mu_0H \parallel c$), measured in NI (a) and GI (b) geometries. (c) Simulated Cr $L_{3,2}$-edge XAS spectra (dashed lines) are overlaid with experimental Cr $L_{3,2}$-edge spectra recorded with right- and left-circularly polarized light. Spectra are vertically shifted for clarity. (d) Simulated XMCD spectrum at 5 K in a 9 T field (NI geometry). The green curve includes ligand-field and charge-transfer effects, whereas the purple curve corresponds to the simulated XMCD obtained without ligand parameters.
• Figure 4: Induced magnetic moment on S and P. (a,b) XAS spectra of CrPS$_4$ measured at 5 K in an applied field of 8 T (normal incidence) at the S $K$-edge (a) and P $K$-edge (b), overlaid with the corresponding LMTO-simulated XAS. (c,d) Corresponding XMCD spectra at the S $K$-edge (c) and P $K$-edge (d), obtained as the difference between right- and left-circularly polarized absorption, and compared with the LMTO-simulated XMCD.
• Figure 5: RIXS measurements and simulations at the Cr $L_{3,2}$ edges. (a) RIXS spectrum measured at the Cr $L_3$ incident energy (peak A, 576.2 eV) at 0 T and 5 K in NI geometry, overlaid with the corresponding fitting components. The labels identify the individual contributions associated with excitations labeled as peaks 1–3. Inset: Simulated RIXS spectrum at the same incident energy, temperature, magnetic field, and geometry. (b, c) RIXS energy-loss maps, obtained as averages of spectra acquired with right- and left-circularly polarized light, across the Cr $L_{3,2}$ edges: (b) experimental and (c) simulated (0 T, 5 K, NI). The maps highlight the crystal-field excitations (red circles) and the charge-transfer excitations (yellow squares).