Abstract
The effects of Mn doping on the microstructure and magnetic properties of CuFeO2 systems were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), and a physical property measurement method. The microstructure measurements demonstrated that the substitution of Mn for Fe can cause lattice distortion, promote grain growth, and change the valence state of Fe and Mn ions. Ceramic samples with doping content x = 0.00−0.03 exhibited two successive magnetic transition temperature (TN) at TN1 ≈ 14 K and TN2 ≈ 10 K. TN decreased gradually with the Mn4+ content, and TN2 was not observed in the x > 0.05 samples within a temperature range of T = 5−300 K. Magnetic hysteresis loops revealed that only anti-ferromagnetic behavior occurred in the low-doped samples (x = 0.00−0.03), and the coexistence of ferromagnetism and anti-ferromagnetism was observed in the high-doped samples (x = 0.05−0.10). Besides, the x = 0.10 sample had a maximum magnetization of 5.98 emu/g. This study provides basic experimental data for investigating the relationship between the microstructure and magnetic properties of CuFeO2 systems.
Highlights
Multiferroic CuFeO2 (CFO) has a triangular lattice anti-ferromagnetic (TLA) structure composed of two layers of O2– and one layer of Cu+ along the c axis in crystallography [1,2]
Seki et al [11] reported that increasing the Al3+ doping concentration significantly improved the ferromagnetism, which was ascribed to the arbitrary distribution of Al3+ in the ferrite hexahedron adjusting the spin structure of CFO systems
Calculated Fe2+ content is approximately 45.62%, 54.45%, 58.92%, 58.52%, and 41.48% for the x = 0.00, 0.01, 0.03, 0.05, and 0.10 samples, respectively. This may be ascribed to the decrease in the oxygen vacancy concentration caused by Mn4+ doping, indicating that the charge neutralization effect caused by Mn4+ doping at the Fe site can induce a different amount of Fe2+ ions in the CFO system
Summary
Multiferroic CuFeO2 (CFO) has a triangular lattice anti-ferromagnetic (TLA) structure composed of two layers of O2– and one layer of Cu+ along the c axis in crystallography [1,2]. J Adv Ceram 2020, 9(4): 444–453 the partial replacement of Fe3+ with Sc3+ induced spin dilution and anti-ferromagnetic phase transition in CFO systems, causing a dimensional crossover of low-energy anti-ferromagnetic excitation from three-dimensional (3D) to two-dimensional (2D) anti-ferromagnetic interactions. Shi et al [12] reported that Ga3+ substitution in Fe3+ sites weakened the anti-ferromagnetic interactions in CFO systems, obviously shifting TN2 to lower temperatures and inhibiting the formation of collinear 4SL ground phases at low temperatures. The substitution of Mn4+ for Fe3+ in CFO systems requires charge compensation, which will influence the creation of cation vacancies and change the system ion valence state, adjusting the effects on the magnetic ground state. Replacing Fe3+ with magnetic Mn4+ ions generates mixed-valence ions caused by the charge balance, dilution effect, exchange interaction, and spin inhibition, affecting competition among ions with different magnetic moments that can enrich the CFO system’s magnetic properties. The interplay between the magnetic properties and microstructure was studied in detail
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