Abstract
Co3+ doping in BiFeO3 is expected to be an effective method for improving its magnetic properties. In this work, pristine BiFeO3 (BFO) and doped BiFe1-xCoxO3 (BFCxO, x = 0.01, 0.03, 0.05, 0.07 and 0.10) composite thin films were successfully synthesized by a sol–gel technique. XRD and Raman spectra indicate that the Co3+ ions are substituted for the Fe3+ ion sites in the BFO rhombohedral lattice. Raman vibration of oxygen octahedron is obviously weakened due to the lattice distortion induced by the size mismatch between two B-site cations (Fe3+ and Co3+ ions), which has an impact on the magnetic properties of BFCxO. SEM images reveal a denser agglomeration in Co-doped samples. TEM results indicate that the average size of grains is reduced due to the Co3+ substitution. XPS measurements illustrate that the replacement of Fe3+ with Co3+ effectively suppresses the generation of oxygen defects and increases the concentration of Fe3+ ions at the B-site of perovskite lattice. Vibrating sample magnetometer (VSM) measurements show that the remanent magnetization (Mr) of BFC0.07O (3.6 emu/cm3) and the saturation magnetization (Ms) of BFC0.10O (48.84 emu/cm3) thin film both increase by approximately two times at room temperature, compared with that of the pure BFO counterpart.
Highlights
Magnetoelectric and multiferroic materials have attracted considerable attention due to their abundant physical properties and potential applications in sensors, spintronic devices, memory devices, magnetoelectric devices, capacitors, nonvolatile logic, etc. [1,2]
Several possible factors may account for the enhancement of magnetic properties for Co-doped BFCxO thin films: (i) an increased Fe–O–Fe spin angle results in the net macroscopic magnetization [25,36,37,38]; (ii) the suppression of the spin cycloid spiral modulation structures will release magnetism [25,26,27,28,29,39]; (iii) enhanced ferromagnetic properties are attributed to the super-exchange interaction between both d6 and d5 electronic configurations of Co3+ and Fe3+ [25,26,27,28,29,39]; (iv) Fe3+ ions are randomly replaced by Co3+ ions, resulting in the non-compensation of the spins on the surface of grains and making grain size closer to or less than the cycloidal modulation wavelength of ~62 nm [25,26,27,28,29,39,40,41,42]
A series of Co-doped BFO thin films were successfully prepared via a facile sol–gel technique
Summary
Magnetoelectric and multiferroic materials have attracted considerable attention due to their abundant physical properties and potential applications in sensors, spintronic devices, memory devices, magnetoelectric devices, capacitors, nonvolatile logic, etc. [1,2]. BFO always shows a long-range spin cycloid structure (Figure 1) because the impurity phases (such as Bi2Fe4O9, Bi24FeO40, etc.) are mixed in its rhombohedral phase, limiting its potential applications [10,11].
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