Magnetic field modulation of photocurrent in BiFeO3 film*

BiFeO3 (BFO) is a kind of room temperature multiferroic material with bulk photovoltaic effect, and it has been a research hotspot in the field of multifunctional materials in recent years. The coexistence of the coupling among magnetic, optical, electrical properties brings rich and complex physical connotations. In this work, BiFeO3 thin film is deposited on FTO substrate by pulsed laser deposition, and the solar cell structure with BiFeO3 film used as light absorption layer and Au film serving as electrode is constructed. X-ray diffraction and Raman spectra indicate that the BFO film grown on FTO substrate has a pure phase structure. The experimental results of physical properties indicate that the BFO film possesses good ferromagnetic and ferroelectric properties and obvious photoelectric effect. According to the hysteresis loop, the remanence (Mr) of the sample is 0.8 emu/cm3, and the coercivity (Hc) is 200 Oe at 300 K. In terms of ferroelectricity, the saturation polarization intensity of the sample can reach 0.997 mu C/cm2, the residual polarization intensity is 0.337 mu C/cm2, and the coercive electric field is 12.45 kV/cm. The above results show that the BFO film has good multiferroic properties. Under solar illumination conditions, the photocurrent density up to 208 mA/cm2 is obtained when a bias voltage 1 V is applied. More importantly, magneto-photocurrent (MPC) effect is found in the BFO film. No matter whether the magnetic field starts to increase from the positive direction or the negative direction, the MPC usually changes with the magnitude of magnetization. When a 1.3 kOe magnetic field is applied, the magneto-photocurrent change rate up to 232.7% is observed under standard solar illumination condition. The results show that the photocurrent of BFO films is greatly improved by a positive magnetic field and negative magnetic field. This magneto-photocurrent effect in BFO thin film comes from the photo-magnetoresistance effect, that is, the photogenerated electrons become spin photoelectrons under the action of an external magnetic field and receive spin-dependent scattering during moving in the conductive band of the material, thus producing the photo-magnetoresistance effect. In addition, the magneto-photocurrent effect is further enhanced by weakening the domain wall scattering of the spin electrons by the magnetic field. This work provides a reference for the modulation effect of magnetic field and light field on the magnetic, optical and electrical properties in multiferroics, and presents a foundation for the research and application of devices in the field of multifunctional optoelectronic materials.