Topological materials, particularly intrinsic magnetic topological systems, are of significant interest due to their potential applications in spintronic devices and quantum computation. While MnBi₂Te₆ has been the primary focus of research in this area, a growing interest exists in Eu-based compounds, including EuSn₂P₂, a magnetic topological system with type-A antiferromagnetic (AFM) order below 30 K. EuSn₂P₂ crystallizes in a layered rhombohedral structure with space group R3m, consisting of strongly magnetic Eu layers sandwiched between Sn-P layers. This study utilizes high pressure as a clean and effective method to tune atomic distances and electronic interactions, inducing potentially interesting quantum phenomena. Previous research has shown pressure's ability to manipulate Néel temperatures and even induce superconductivity in various materials. This research systematically investigates the high-pressure behavior of EuSn₂P₂ using angular-dispersive X-ray diffraction (XRD), time-domain synchrotron Mössbauer spectroscopy (SMS), partial fluorescence-yield X-ray absorption spectroscopy (PFY-XAS), and computational methods to understand the interplay of crystal structure, magnetic ground state, and valence state under pressure.

The literature review highlights the importance of intrinsic magnetic topological materials for spintronics and quantum computing. It mentions MnBi₂Te₆ as the main studied material and introduces EuSn₂P₂ as a promising alternative with type-A antiferromagnetic order below 30 K. The review also cites previous research demonstrating pressure's effectiveness in tuning material properties, such as inducing superconductivity or modifying Néel temperatures.

The study employed multiple techniques to investigate EuSn₂P₂ under high pressure. High-resolution XRD experiments were conducted using a diamond anvil cell (DAC) with helium and neon as pressure-transmitting media, reaching pressures up to 62 GPa. Rietveld refinement was used to analyze XRD data. Time-domain synchrotron Mössbauer spectroscopy (SMS) was performed at the 3ID Beamline of the APS to study the magnetic state of Eu ions, analyzing spectra using CONUSS software to extract magnetic hyperfine fields and quadrupole splitting. Partial fluorescence-yield X-ray absorption spectroscopy (PFY-XAS) at the Eu L₃ edge was used to determine the valence state of Eu ions under pressure. Molecular orbital calculations were performed to analyze chemical bonding evolution under pressure and electronic band structure calculations using GGA+U with spin-orbit coupling were used to study the surface states and spin texture of EuSn₂P₂.

High-pressure XRD revealed a rhombohedral-to-amorphous phase transition at 36 GPa, persistent up to 62 GPa. SMS showed a remarkable fourfold increase in magnetic ordering temperature (T₀) from 30 K at ambient pressure to 130 K at 41.2 GPa, this increase being maintained even in the amorphous phase. Analysis of SMS data indicated that the direction of Eu spins remained in-plane up to 42.7 GPa. PFY-XAS experiments revealed a transition of Eu ions from a mostly divalent state at lower pressures to an intermediate valence state above 20 GPa. Molecular orbital calculations illustrated pressure-enhanced Eu-Sn bonding, contributing to increased RKKY interaction and hence higher T₀. Band structure calculations showed that both changes in lattice parameters and magnetic configuration could influence topological properties.

The dramatic increase in T₀ under pressure is primarily attributed to the enhancement of RKKY interactions due to stronger Eu-Sn bonding. The persistence of magnetic order in the amorphous phase is consistent with observations in other amorphous magnets. The change in Eu valence from divalent to intermediate valence at higher pressures suggests a complex interplay between electronic structure and magnetic properties under compression. The observed in-plane spin orientation suggests that changes in topological properties are primarily influenced by lattice parameter changes rather than spin canting.

This comprehensive high-pressure study of EuSn₂P₂ reveals a pressure-induced amorphization and a dramatic enhancement of its magnetic ordering temperature. The findings highlight the significant impact of pressure on the interplay of crystal structure, magnetic order, and valence state in this topological magnet. Future studies could explore the potential for superconductivity under pressure and further investigate the relationship between the pressure-induced changes and the topological properties of EuSn₂P₂.

The presence of a minor oxide impurity phase in one of the datasets might slightly affect the quantitative interpretation of some results. While the study provides strong evidence for the change in Eu valence, a more precise quantification would require detailed electronic structure calculations.