The Study On Preparation And Magnetic Properties Of Co-Based Alloy Thin Films

The high spin polarizability material is used as the perpendicular magnetic tunnel junction(P-MTJ)to improve the tunneling magnetoresistance(TMR).The high magnetocrystalline anisotropy material is used as a magnetic recording medium to improve the thermal stability of the memory cell,which avoids the superparamagnetic effect caused by the reduction in the size of the recording unit.In this work,the Heusler-type spin gapless semiconductor(SGS)CoFeMnSi and the high magnetocrystalline anisotropy Co-based(Co-Zr,Co-Hf system)permanent magnetic material were studied in detail.The Ta/Pd/ferromagnetic laer/NgO/Pd multilayers were fabricated on Si substrate by magnetron sputtering.The perpendicular magnetic anisotropy properties of the three systems were discussed in detail by changing the thickness of ferromagnetic layer,the thickness of MgO,annealing temperature and interface structure.The effect of hydrogen on the magnetic properties of CoFeMnSi film with perpendicular magnetic anisotropy(PMA)was studied.The permanent magnetic properties of Co-Zr and Co-Hf films were improved by C and N doping.The main achievements are shown as below:Firstly,the effects of annealing temperature,CoFeMnSi thickness,MgO thickness and Pd/CoFeMnSi and CoFeMnSi/MgO interface on the PMA of CoFeMnSi film were investigated by controlling the preparation process.The results show that the Ta/Pd/CoFeMnSi(2.3 nm)/MgO(1.3 nm)/Pd film annealed at 300 ? has the strongest PMA,its rectangularity is 0.95 and Keff value is 0.557×106 erg/cm3.Changing the test atmosphere find that hydrogen has a significant influence on the magnetic properties of Ta/Pd/CoFeMnSi(2.3 nm)/MgO(1.3 nm)/Pd film annealed at 300? whose residual magnetization(Mr)decrease from 123.15 emu'cm3 to 30.75 emu/cm3 with H2 concentration of 5%,and the PMA of the sample is weakened.The magnetic properties of the sample have good recoverability after removal of hydrogen.Secondly,the permanent magnetic properties of CoZr thin films were studied.[CoZr(2 nm)/C(5 nm)]4 multilayers were prepared by introducing C films into CoZr thin films with Co and Zr atomic ratio of 14.31:2.The coercivity of[CoZr(2 nm)/C(5 mn)]4 multilayers annealed at 650 ? is 733 Oe.Based on the results of PMA of CoFeMnSi film,the Ta/Pd/CoZr(4.0 nm)/MgO/Pd multilayers was prepared.After annealing at 300 ? a strong PMA effect was obtained and the coercivity under the magnetic field parallel to the film plane is 1214 Oe;microstructure analysis shows that MgO can regulate the local chemical composition of CoZr film,which promotes the formation of Co11Zr2 permanent magnetic phase.Based on the results of CoZr thin film,the permanent magnetic properties of CoHf thin film were further studied.The coercivity of 722 Oe CoHf film with Co and Hf atomic ratio of 7.14:1 was obtained by doping the N element into CoHf film by reactive sputtering.Introducing C film to prepare[CoHf(2 nm)/C(8 nm)]4 multilayers annealing at 650 ? can increase the coercivity to 758 Oe;microstructure analysis shows that the coercivity is derived from the Co7Hf phase.Ta/Pd/CoHf(4.0 nm)/MgO/Pd sample annealed at 300 ? could obtained a strong PMA effect and had a high coercivity of 1229 Oe with the magnetic field parallel to the film plane.