Tuning the magnetic ground state of CuCrO2 by Ge substitution

Abstract

Polycrystalline CuCr_0.95Ge_0.05O₂ was synthesized by a conventional solid-state reaction. X-ray diffraction confirmed the rhombohedral delafossite structure (R–3m). The refined lattice parameters are nearly identical to standard values, indicating Ge incorporation with minor distortion. Scanning electron microscopy (SEM) revealed hexagonal-like grains averaging of 3.6 ± 0.9 μm. Magnetic characterization showed weak ferromagnetism at low temperatures and paramagnetism at room temperature. Zero-field-cooled susceptibility identified a Curie temperature (T_C) of 139.3 ± 0.4 K, and Curie–Weiss fitting yielded a Curie constant (C = 1.425 ± 0.002), a Curie–Weiss temperature (Θ = −138.8 ± 0.4 K), and an effective magnetic moment (μ_eff = 3.37 μ_B), consistent with the Cr³⁺ sublattice. Additional field-dependent magnetization (M–H) loops near T_C revealed hysteresis in the 110–135 K range, with coercivity decreasing nearly linearly with temperature. Extrapolation yielded T_C = 139.8 ± 3.6 K, consistent with susceptibility results. These findings demonstrate that Ge substitution preserves the delafossite structure of CuCrO₂ while inducing weak ferromagnetic ordering, offering a route to tune the magnetic ground state.