Sanjay Singh

Cr1+δTe2, a family among two-dimensional (2D) van der Waals (vdW) transition-metal dichalcogenides, has garnered significant interest owing to its tunable structural, electrical, and magnetic properties controlled by the concentration of self-intercalated Cr atoms. Among various external stimuli, pressure provides an additional route to tune the associated physical properties of these materials through modifications of interatomic distances, which can substantially alter the electrical and magnetic properties. In the present study, we report the theoretical and experimental investigation of the pressure-induced structural and electrical properties of Cr1.28Te2 with trigonal (P3̅m1) crystal structure. The pressure-dependent synchrotron X-ray powder diffraction (SXRPD) analysis revealed iso-structural transitions at ∼4.7, ∼9.9, and ∼19.7 GPa, evidenced by the deviation of lattice parameters from linear pressure dependence. The temperature-dependent resistance curves measured over a range of applied pressure show the presence of metal-semiconductor-metal transition near ∼7.8 and ∼16.8 GPa, close to the pressures of the iso-structural transitions. Additionally, a low-temperature resistance minimum observed at low pressures suggests the emergence of localization-related effects. The resistance minimum gradually shifts toward higher temperatures with increasing pressure, indicating the progressive enhancement of localization effect under compression. Further, theoretical calculations suggest that the metallic nature of Cr1.28Te2 below the metal-semiconductor transition (i.e., at low pressure) is dominated by Cr2–3d states, whereas above the transition (at high pressure), the metallicity is governed by Te–3p states. A nonmonotonic evolution of the magnetic state is also observed under pressure, which is likely to originate from modified exchange interactions due to the change in bond lengths under applied pressure. Overall, the combined experimental and theoretical results provide a detailed insight into pressure-induced structural and electrical properties of Cr1.28Te2.

We report an unusual room temperature giant zero-field-cooled exchange bias (∼1 kOe) in an antiferromagnetic (100 − x)YBaCuFeO5–ferrimagnetic (x) Ni0.3Zn0.7Fe2O4 composite. The solid state route is adopted to prepare these dilute weight% (x = 1, 3, and 5) ferrite based composites. The incorporation of ferrite phase improves the interfacial tensile strain and grain boundary volume fraction in the said composite. The incommensurate to commensurate magnetic transition (TN2) of YBaCuFeO5 is shifted to a high temperature by 10 K with the lowest concentration and indistinguishable in higher concentrations due to the magnetic dominance of ferrites. The irreversibility of magnetization due to the field history mostly stems from the uncompensated spins and a competitive interaction among the magnetic phases at the interface. The magnetic isotherms show unusual negative exchange bias phenomena in the said system, and a large room temperature spontaneous exchange bias (∼1 kOe) is achieved with a dilute incorporation x = 5. The exchange bias field and coercive fields (HC) are, however, contrary to each other with temperature (and concentration) explained with a schematic model on the basis of dominating irreversible spins at high temperatures. In a field of ±50 kOe, the exchange bias field is dropped, while HC is increased, which might be due to the dominance of Zeeman energy over the uniaxial anisotropy. The non-collinear magnetic phase transition of YBaCuFeO5 at T ≤ 175 K plays a pivotal role in reducing the exchange bias compared to its collinear phase (300 K). Moreover, the extent of this bias field (∼1 kOe) can be considered a useful component in efficient device fabrication.