Fe3O4/MgO(100)薄膜外场诱导电阻变化特性

Resistance characteristics of Fe_3O_4/MgO(100) films at action of outfields

采用激光分子束外延(L-MBE)方法,以MgO(100)为基底生长了Fe3O4单晶薄膜,研究了Fe3O4/MgO(100)薄膜外场(温度、磁和激光场)诱导电阻变化特性。X射线衍射(XRD)分析表明Fe3O4薄膜是沿MgO(200)晶面外延生长的单晶薄膜;反射高能电子衍射(RHEED)强度振荡曲线分析表明Fe3O4薄膜表面平整,而且生长模式为2维层状生长;原子力显微镜(AFM)分析表明Fe3O4薄膜表面粗糙度为0.201 nm,说明薄膜表面达到原子级平整度。外场作用下Fe3O4薄膜的电阻测试表明:薄膜样品的电阻在120 K(Verwey转变温度)出现一峰值,略微下降后继续增大,展现出半导体型的导电特性;在激光作用下,整个测量温度范围内薄膜样品的电阻减小,样品展示出瞬间光电导的特性;从降温曲线可以看出,Verwey转变温度由无激光作用时的120 K上升到有激光作用时的140 K;光致电阻变化率随着温度的降低而增大,这主要是由于激光作用导致电荷有序态的退局域化。

The outfield-induced resistance properties of Fe3O4/MgO（100） films were investigated.The Fe3O4 thin films were grown on MgO（100） substrates by laser molecular beam epitaxy（L-MBE）.The Fe3O4 epitaxial film could be grown with the（200） face of MgO substrate as indicated by XRD analysis.The quality of the films was checked in situ by monitoring reflection high energy electron diffraction（RHEED） patterns and intensity oscillation during deposition.The results show that the film surface is plat,and the film growth mode is 2D layer-by-layer.AFM analysis reveals that the RMS roughness of the films is about 0.201 nm,which shows that the film surface is plat at atom level.The resistance of the films was investigated at the action of outfields such as magnetic field,temperature field and laser field.The results show that,the resistance of the films decreases generally as the temperature increases,while it has a peak at 120 K（known as the Verwey transition temperature）,showing the films＇ electrical character of semiconductor type.The resistance of the films decreases with laser field in the temperature range of 50-300 K,so the films show an instantaneously photoconductive character.The Verwey transition temperature is at 120 K for the laser off,but it ascends to 140 K for the laser on.The photoinduced resistance（PR） change increases with the temperature declining,which is due to the field-induced delocalization of charge ordered states in the films.