Electronic Transport Properties In Fe Nanocluster-Assembled Granular Films

Magnetic granular films have borad application propects in spintronic devices including magnetic field sensors,magnetic detectors,high density magnetic read/write heads and magnetic random access memories,because of their abundant electronic transport properties,such as giant magnetoresistance(GMR)effect,anomalous Hall effect(AHE)and giant Hall effect(GHE).However,due to the limitations of preparation methods,the researches concentrating on the influence of granular size,granular spacing and interface on electronic transport properties are rarely reported.Therefore,it is significant for both academic research and industrial application to look for a new method,which can individually control the granular size,granular spacing and interface,and systematically investigate the influence of mircostructure on electromagnetic transport properties.In this work,Fe nanocluster-assembled granular films with different oxidation degree were prepared by using a plasma-gas-condensation cluster deposition system.Fe-Cr nanolcuster-assembled granular films with different Cr volume fraction(x)were achieved by the novel in situ assembly technology.In this method,the uniform Fe nanoclusters obtained by plasma-gas-condensation technonlogy were coated with a Cr layer by conventional magnetron sputtering in situ in a vacuum.The influence of Cr volume fraction on the electronic transport properties of the Fe-Cr granular films was systematically studied.The main research contents are as follows:(1)Fe nanocluster-assembled granular films with different oxidation degree were prepared by using a plasma-gas-condensation cluster deposition system through tunning the oxygen flow rate(fo)in deposition chamber.The conductive patterns of Fe nanocluster-assembled granular films could be divided into metal region,transition region and insulator region in terms of the degree of oxidation.The temperature-dependent resistivity behavior in the metal region could be attributed to the mechanism incorporated with the thermal fluctuation-induced-tunneling(FIT)conduction process and temperature-dependent scattering effect.In the insulator region,a linear dependence of log σ on 1/T in the range of 5≤T≤50K was observed,which could be ascribed to uniform Fe core size and iron oxide shell thickness.Magnetoresistance(MR)of Fe nanocluster-assembled films increased with increasing fo because of the enhancement of spin-dependent interface scattering.(2)Fe-Cr nanolcuster-assembled granular films with different x were fabricated by using a plasma-gas-condensation cluster deposition system.In the Fe-Cr nanocluster-assembled granular films,both the longitudinal resistivity(ρxx)and Hall resistivity(ρxy)first increased and then decreased with increasing x,and reached a maximum value at 0.26(ρxx =2×104 μΩcm,ρxyA=9.55μΩcm).The initial increase of resistivity could be ascribed to the enhancement of surface and interface scattering caused by the coated amorphous Cr layer,and then the decrease of resistivity could be explained by the shunting effect and short circuit effect due to the formation of continuous Cr films.In addition,we found that the tunneling effect must be deducted from longitudinal resistivity as the AHE scaling relation was established.After deducting the tunneling effect,the AHE scaling factors also first increased and then decreased with increasing x.The results showed that the tunneling behavior had no effect on AHE but the surface and interface scattering played an important role in effectively increasing AHE.