Magnetic dilution and low-temperature vibrational behavior in Ga-substituted NdCrO3

Abstract

Rare-earth orthochromites are functional oxides in which magnetic ordering, rare-earth moments, octahedral distortions, and lattice vibrations are closely coupled. In this study, we examine the effect of non-magnetic Ga³⁺ substitution on the structural, magnetic, and vibrational properties of NdCrO₃. Ga-substituted NdCr_1-xGa_xO₃ ceramics with x = 0.0–0.5 were prepared by the conventional solid-state reaction method. X-ray diffraction and Rietveld refinement confirm that all compositions retain the orthorhombic Pbnm structure. Only minor changes in the lattice parameters are observed, consistent with the close ionic radii of Ga³⁺ and Cr³⁺. Magnetic measurements show that the Néel temperature remains nearly unchanged, decreasing slightly from about 225.2 K for x = 0.0 to 223.3 K for x = 0.5. This behavior is consistent with the preservation of long-range Cr–O-Cr antiferromagnetic ordering. In contrast, the spin-reorientation transition becomes broader and shifts from approximately 37.1 K to 31.2 K with increasing Ga content. This trend reflects a gradual weakening of the magnetic exchange balance involving the Nd and Cr sublattices. Exchange bias is observed in the system, and the maximum bias field decreases from about 2300 Oe for the undoped sample to 330 Oe for x = 0.5. The reduction in exchange bias reflects weakened inter-sublattice magnetic coupling after B-site magnetic dilution. Raman spectroscopic analysis reveals low-temperature anomalies in the phonon frequency and linewidth, confirming the presence of spin-phonon coupling in the system. Despite changes in magnetic behavior, the spin-phonon response remains comparatively robust against Ga content. Overall, the results show that Ga substitution can tune the magnetic properties of NdCrO₃ without strongly disturbing its lattice dynamics.