铁酸铋薄膜光电流的磁场调制研究

Magnetic field modulation of photocurrent in BiFeO_(3) film

BiFeO_(3)作为一种具有体光伏效应的室温多铁材料,是近年来多功能材料领域的研究热点.其中磁、光、电等多种性能之间耦合作用的共存带来了丰富而复杂的物理内涵.利用脉冲激光沉积在导电玻璃(SnO_(2):F,FTO)衬底上沉积了BiFeO_(3)薄膜,实验结果表明,该薄膜具有良好的铁磁和铁电性能,并通过磁场实现了对薄膜光电性能的调控.在标准太阳光照的同时施加1.3 kOe(1 Oe=10^(3)/(4π)A/m)磁场下,磁-光电流变化率达到232.7%.BiFeO_(3)薄膜中的磁-光电流效应来自于光磁电阻效应,即光生电子在磁场作用下成为自旋光电子,在材料导带运动过程中受到自旋相关散射而具有光磁电阻效应;此外,磁场作用使这些自旋光电子受到的畴壁散射减弱也进一步增强了磁光电流效应.本文为磁场、光场调控多铁性薄膜的磁、光、电等物理特性提供了参考,为多功能光电材料领域的器件研究与应用提供了基础.

BiFeO_(3)(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,BiFeO_(3) thin film is deposited on FTO substrate by pulsed laser deposition,and the solar cell structure with BiFeO_(3) 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/cm^(3),and the coercivity(Hc)is 200 Oe at 300 K.In terms of ferroelectricity,the saturation polarization intensity of the sample can reach 0.997μC/cm^(2),the residual polarization intensity is 0.337μC/cm^(2),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/cm^(2) 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.