95 Research Summary: Probing the Mechanism Of Colossal Magnetoresistance in EuCd₂P₂ Via High-Pressure Transport Measurements

Faculty Mentor: Shanti Deemyad (Physics & Astronomy, University of Utah)

This thesis presents a comprehensive high-pressure study of the layered antiferromagnet EuCd₂P₂, a phosphide compound that exhibits colossal magnetoresistance (CMR) in the absence of mixed valence, Jahn-Teller distortions, or a perovskite structure. Using diamond anvil cells (DACs) combined with cryogenic transport and AC magnetic susceptibility measurement systems, we have mapped the pressure–temperature phase diagram of EuCd₂P₂. I will discuss how these results provide insight into the interplay between magnetic ordering, anisotropic lattice compression, and electronic transport.

High-resolution synchrotron X-ray diffraction (XRD) reveals that EuCd₂P₂ retains its trigonal P3̅*m1 symmetry up to 14.9 GPa, with no structural phase transitions. However, anisotropic lattice compression and subtle anomalies in the lattice parameters suggest a pressure-induced isostructural transition that likely enhances interlayer Eu–Eu magnetic exchange. In both AC susceptibility and resistivity data, I observe a sharp, pressure-dependent shift in the Néel temperature (Tₙ) from 11 K at ambient pressure to nearly 20 K at 5 GPa, confirming that magnetic order in EuCd₂P₂ is highly tunable via compression.

The resistivity peak, associated with magnetic scattering, tracks the magnetic transition closely and shows a dramatic suppression in magnitude with pressure—indicating enhanced metallicity and reduced spin disorder. Together, these findings demonstrate that CMR in EuCd₂P₂ arises not from structural transitions but from pressure-enhanced magnetic fluctuations and spin-carrier coupling. The sharpness of both the temperature and field dependence of this effect positions EuCd₂P₂ as a promising material for low-temperature magnetic sensors and antiferromagnetic spintronic devices.

This work supports the establishment of EuCd₂P₂ as a rare example of fluctuation-driven CMR in a structurally stable, low-carrier system, advancing the understanding of spin-mediated transport in quantum materials and providing a platform for future studies of topological, magnetic, and correlated phenomena under extreme conditions.