Preparation And Electronic And Magnetic Properties Of Sr₂MoCrO₆ Thin Films

Double perovskite oxides are known for their novel physical properties,such as superconductivity,high electronic conductivity,low magnetic coercivity,room temperature ferrimagnetism,and large tunneling negative magnetoresistance.Recently,double perovskite system is attracting growing attentions for the coupled spin and charge degree of freedom,which is very important to the potential application in the spintronics.Therefore,we studied the thin film growth and magnetotransport properties of the chromium-based double perovskite Sr₂MoCrO₆(SMCO).In this thesis,(001)-oriented single crystal strontium titanate was employed as substrates to grow high quality SMCO thin films.The pulsed laser deposition(PLD)based growth conditions are optimized to achieve the best conductivity of SMCO sample.The main research results are as follows:(1)We explored the SMCO thin film deposition condition and obtained the high quality epitaxial thin films with excellent electronic conductivity.The optimized growth conditions for the SMCO films are:the pressure in chamber is 5×10^-5 Pa,the laser pulse energy is 90 m J and the substrate temperature is 775?.The SMCO thin film samples obtained under the aforementioned conditions have excellent crystallization quality and electrical conductivity.By X-ray rocking curve analyses,the best thin film shows peak width at half-maximum of 0.048°.The room temperature resistivity of the best crystallized thin film is 10^-7?cm,demonstrating good metallic conduction behavior,in which the large low temperature magnetoresistance is also observed.(2)SMCO films with different thicknesses(6-216 nm)were prepared under optimized conditions for systematic structural,magnetic and magnetotransport study.The SMCO films are epitaxial and have an excellent crystallization quality.The minimum surface mean square root roughness of SMCO thin film is 0.2 nm.The carrier concentrations of the thin films are between 10²¹-10²³ cm^-3,and the mobilities are between 10²-10⁴ cm²/Vs.The magnetic properties of 72-nm thin film sample were measured,in which we confirmed the ferrimagnetic ordering.Theoretical calculations show that the electronic band structure of SMCO is semi-metal,which means the Fermi surface is fully spin polarized.In 72 nm SMCO thin film,the magnetoresistance exceeds 1600%at 2 K and 14 T.In sufficiently large magnetic fields,the high-mobility electrons form cyclotron orbits,which drift in the electric field.Due to the half-metallic band structure,the drifting cyclotron orbits interact with the domain walls,and could be scattered efficiently.The spin-spin interaction of drifting orbits and domain walls describe the electron dynamic picture in SMCO,and therefore lead to linear magnetoresistance.