Neutron scattering investigation of the modulated magnetic phase in monoclinic Cr₅Te₈ and how it relates to the large magnetoresistance
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[EMBARGOED UNTIL 12/01/2026] There is extraordinary interest in developing metallic 2D van der Waals materials that exhibit room-temperature ferromagnetism (FM) with perpendicular magnetic anisotropy (PMA). Such systems could be incorporated into 2D van der Waals materials engineering with the potential for spin control and spintronic applications. Cr₅Te₈ is among a family of such materials that displays a rich variety of magnetic and electronic phenomena. In this work, neutron scattering measurements reveal the emergence of a modulated magnetic phase in Cr₅Te₈ immediately above the FM transition temperature (Tc = 155 K). This modulation develops along the vdW stacking axis and persists over a short temperature range (155 K - 180 K). This coincides with the onset and disappearance of the giant magnetoresistance (GMR) effect observed in [2], demonstrating a relationship between the two. The application of a magnetic field along the stacking direction suppresses the modulation and restores the uniform FM phase, thereby acting as a switch that reduces the resistivity in a manner analogous to the transition from the paramagnetic (PM) to FM state. At low temperatures (TN = 70 K), the antiferromagnetic (AFM) phase of Cr₅Te₈ is modeled for the first time. Refinement of the magnetic structure reveals a small, highly disordered moment on an interstitial Cr site (0.82 μb). In addition, clear evidence of the two-dimensionality of the Ferromagnetism in the molecular CrTe₂ layers is revealed by magnetic diffuse scattering. Investigating both an in-plane and an out-of-plane reflection, allows for the separation of contributions from different components of the magnetic moment. These give rise to markedly different diffuse scattering behavior, revealing two distinct types of coexisting short range order. Diffuse scattering from the out-of-plane components display correlations of ≈11Å centered on the Bragg reflection and persists up to the highest measured temperature of 250 K disappearing at the onset on the FM ordering. Diffuse scattering from the in-plane component originates from the magnetic modulation and continues to a much lower temperature (< 80K), shows correlations of ≈40 Å, and is centered at the modulated phase's satellite reflections.
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Ph. D.