Investigation of room temperature ferromagnetism in transition metal doped BiFeO₃

Abstract

Spintronic functionality in ferromagnetic materials is a next-generation technique, to be used in data storage, high-frequency communications, and logic devices with minimum energy consumption. Ultra-low energy consumption in high-speed logic devices can be envisioned by inducing ferromagnetic behavior into room temperature multiferroic materials. However, there is a scarcity of room temperature multiferroic materials which have a definite spin degree of freedom. To fully exploit these technological challenges, we introduce the induced ferromagnetism in bismuth ferrite (BiFeO 3 , BFO) by doping transition metal (Cr, Ni, Co) elements. Our investigation initiates with the experimental study on chemically synthesized BiFe (1−x) M x O 3 samples where x = 0.0625 (6.25%) and M = Cr, Ni and Co. Experimental findings are verified by theoretical simulation using density functional theory (DFT + U) and gauge including projector augmented wave (GIPAW) based calculation. All the experimental studies are done at room temperature while the theoretical verification using DFT is carried to understand the underlying mechanism behind the magnetic behavior of doped BiFeO 3 . It is done by optimizing the structural parameters comparable to the room temperature values. Microstructural and magnetic properties are studied using x-ray diffraction (XRD), transmission electron microscopy (TEM) and Vibrating sample magnetometer (VSM). All these experimental studies confirm the structural changes and induced ferromagnetism with doping. X-ray photoelectron spectroscopy (XPS) verified the reason behind this ferromagnetic property on the basis of oxygen vacancy content. Electron paramagnetic resonance (EPR) spectroscopy shows the tuning of Δg values due to enhanced magnetization.The density of states (DOS) calculations were performed on BFO (band-gap 1.89 eV) after structural optimization using DFT + U method, confirm our experimental findings. Magnetic moment values change drastically with doping elements (M), i.e. almost negligible for BFO (antiferromagnetic) to maximum (2.85 μ B /f.u.) for Ni-doped sample. We also compute the EPR g-tensor using GIPAW method to confirm the tuning of Δg values due to enhanced magnetization. These results can highlight the impact and importance of suitable transition element doping to induce the room temperature ferromagnetism in BiFeO 3 .

Surface Modification and Enhancement of Ferromagnetism in BiFeO3 Nanofilms Deposited on HOPG

“…In the O1s spectrum in the region of ~ 532.2 eV, there is a wide peak characterizing the surface defects in the BFO phase corresponding to V o [ 72 ]. From the XPS analysis, it can be seen that when annealed in vacuum, bismuth corbanate or bismuth oxide is not reduced to metallic, but forms a triple compound with iron and oxygen, possibly due to the formation of oxygen and bismuth vacancies [ 73 ].…”

Suppression of the Cycloidal Spin Arrangement in BiFeO3 Caused by the Mechanically Induced Structural Distortion and Its Effect on Magnetism

“…It is known that the particle size reduction of BiFeO 3 below the typical period length of ∼62 nm can lead to the suppression of its spiral spin structure, resulting in the ferromagnetic behavior of the nanomaterial (Mazumder et al, 2007;Park et al, 2007;Zhong et al, 2010;Castillo et al, 2013;Huang et al, 2013;Landers et al, 2014;Li et al, 2019). Additionally, the destruction of the cycloidal spin arrangement in BiFeO 3 can be induced by the crystal lattice distortion provoked by atom doping (Widatallah et al, 2014;Mao et al, 2016;Ting et al, 2017;Godara et al, 2018;Sharma et al, 2019;Xian et al, 2019;Dubey et al, 2020;Fertman et al, 2020;Sánchez-De Jesús et al, 2020). The present work gives evidence of the fact that the suppression of the cycloidal spin configuration in BiFeO 3 with the average particle size exceeding λ can also by caused by the mechanically induced crystal lattice distortion.…”

Enhanced hydrogen evolution reaction in Sr doped BiFeO3 by achieving the coexistence of ferroelectricity and ferromagnetism at room temperature

“…The magnetic performance of samples shows an increasing tendency, the saturation magnetization of pure BiFeO 3 and Sr-doping Bi 1-x Sr x FeO 3 (x = 0.05, 0.1, 0.15) gets to 105, 118, 140, 159 emu/cm 3 , respectively. The difference in studied samples for the magnetic behavior results from different degree of FeO 6 octahedrons distortion via diverse Sr-doping content [11]. Magnetic behavior of BFO originates in two adjacent Fe 3+ along the (111) rotation to generate the net magnetic moment [13,14].…”

“…It is well known that Bi element volatiles easily from the stoichiometry BFO, which results in the existence of oxygen vacancies [5,[23][24][25]. As the bridge of double exchange, oxygen vacancy harms the ferromagnetism enhancement [11][12][13][14]. After Sr doping, the oxygen vacancy compensation seems to be happened as the Bi chemical weight is decreased, this increased content of oxygen is corresponding to the overall ferromagnetic enhancement via the strengthen of the double exchange, although the Fe 3+ /Fe 2+ ratio is growing monotonously by our experimental results [26,27].…”

“…Owing to the internal electric field and the multiple valence states of Fe, the most two important factors for charge transfer in a water-splitting catalyst, BFO deserves a comprehensive study in the HER. Besides, the +2 valence alkaline-earth metal introduces more Fe 3+ ions and oxygen charge compensation, which lowers the resistance benefiting the possible electrocatalysis activity and contributes to enhancement of the magnetic property [11,12].…”