Compositional dependence of structural, magnetic and spin-phonon coupling properties in Fe2−xGaxO3 (x = 0.6–1.2) system with orthorhombic symmetry.

• The mechanical alloying reduced the sintering temperature to stabilize orthorhombic phase. • The site occupancy of Fe and Ga ions controlled ferrimagnetism, soft and hard magnetic phases. • The low temperature magnetic peak appeared due to magnetic frustration and anisotropy. • The extra moment with reference to spin value suggested contribution for orbital moment. • The ferrimagnetism and spin-phonon coupling indicated multiferroelectric nature in the system. A combined technique of mechanical alloying and heat treatment has been used to prepare the polycrystalline samples of Fe 2−x Ga x O 3 (x = 0.6–1.2) system in orthorhombic phase. It has been possible to reduce the sintering temperature by ~350 °C for stabilizing the orthorhombic phase in comparison to the temperature reported in literature. The Rietveld refinement of X-ray diffraction patterns indicated the distribution of Ga and Fe atoms in the Ga1, Ga2, Fe1 and Fe2 sites of the lattice structure. A linear variation of the lattice parameters with Ga/Fe content showed application of Vegard's law. The temperature-dependent magnetization measurements confirmed ferrimagnetic order of Fe spin moments. The ferrimagnetic transition temperature (T C) has decreased from 320 K to 100 K with the increase of Ga content in the range of x = 0.6–1.2. Temperature-dependent Raman spectroscopy data ruled out any structural phase transition at T C , but an anomalous behaviour of the position and width of the peaks of Raman active phonon modes near to T C confirmed a strong spin–phonon coupling in the material. The spin–phonon coupling strength (η) for the A9 mode has been found around 1.64 cm−1 for x = 1 and 3.34 cm−1 for x = 0.8, and η for the A21 mode has been found around 2.12 cm−1 for x = 1 and 3.28 cm−1 for x = 0.8. The spin-phonon coupling strength has been diluted in the samples with higher content of Ga. The experimental results indicated that the variation of Ga/Fe content and its distribution in lattice sites determine the ferrimagnetic properties, magnetic anisotropy and spin-phonon coupling in Fe 2−x Ga x O 3 system. The results are expected to be useful for understanding the spin-phonon coupling in multiferroic-magnetoelectric materials with magnetic and electric transitions near to room temperature. [ABSTRACT FROM AUTHOR]