Studies On Magnetic Properties Of Spintronic Materials Grown By PLD

By combining the characteristics of spin and charge in electron, spintronics will extend the traditional electronics field and make semiconductor devices with faster operation speed, lower power consumption and higher integration, thus has broad application prospects. Ferromagnetic materials with high spin polarization or magnetic semiconductors with room temperature ferromagnetism are attracted in spintronics. This work is concentrated in the investigtion of corresponding materials from these two aspects, respectively. γ’-Fe4N and defect induced MgO and SnO2magnetic semiconductors were prepared by pulsed laser deposition (PLD). The structrue and magnetic properties were investigated.y’-Fe4N exhibits high spin polarizatin both theoretically and experimentally, which has potential applications in spintronic devices. PLD is a facile method to grow metallic films with special structure under nonequilibrium conditions. In the presant work, γ’-Fe4N films were prepared by PLD technique. It is found that the kind of buffer material and the preparation parameters take great effect on the phase formation and the magnetic properties.Firstly, Fe-N films deposited with an nitrogen pressure of8mTorr on various buffer layers show different structure and magnetic property. Pure γ’-Fe4N was prepared on the thermal oxided silicon wafers at200℃. The Fe-N film deposited on room temperature growing MgO buffer exhibits Ms value of1713emu/cm3. However, the Fe-N film deposited on600℃growing MgO buffer shows Ms value of1441emu/cm3. XRD demonstrated that the Fe-N films are both make up of α-Fe and γ’-Fe4N. Furthermore, it is found that single phase γ’-Fe4N can be obtained on MgO buffer with Pn2of17mTorr.Then, the effect of the deposition temperature of MgO buffer on the structure and properties of γ’-Fe4N film was investigated. The γ’-Fe4N films deposited with MgO buffer grown at600℃exhibit an in-plane magnetic anisotropy while the film deposited with MgO buffer grown at RT has nearly isotropic magnetic properties.The cubic magnetic anisotropy of the γ’-Fe4N films deposited with MgO buffer grown at600℃is correlated with the (001)-oriented γ’-Fe4N film grown epitaxially on the textured MgO buffer layer formed at high growth temperatures. This result is essential for its potential applications in the devices. On the other hand, defect induced MgO and SnO2magnetic semiconductors were prepared by PLD, the origin of the ferromagnetism was studied.The crystallinity dependence of room-temperature ferromagnetism (RTFM) in pure MgO thin films were investigated. All the samples deposited from RT to200℃show clear RTFM, and the magnetization decreases monotonically with the increase of the substrate temperature, whereas the MgO film grown at300℃shows diamagnetism behavior. The maximum Ms of8emu/cm3is obtained for the MgO film deposited at RT, which degrades dramatically after crystallization under the annealing in both vacuum and air atmosphere. Further photoluminescence and X-ray photoelectron spectroscopies reveal that the ferromagnetism in the MgO thin filmns is correlated directly with the Mg vacancies. A direct correlation between the RTFM, the crystallinity, and Mg vacancies in the MgO films has been established. By investigating the magnetic property of the amorphous MgO fims deposited under different temperatures, the consistency of the variation of the Mg vacancies concentration and Ms value of the samples demonstrates that the origin of the RTFM could be attributed to the non-stoichiometry and Mg vacancies in the amorphous MgO films. It is concluded that the Mg vacancy is the origin of the RTFM of MgO films. Furthermore, the RTFM can be tuned by changing the deposition temperature and the oxygen pressure, which makes good foundation for the d0ferromagnetism research and future applications in spintronics devices.The magnetic property of pure SnO2film decreased with deposition temperature firstly, then incresed with further increasing temperature. With PL analysis, the defects will affect the magnetism in two aspects. On one hand, there are more oxygen vacancies for the samples with less crystallinity deposited at lower temperature, so the magnetistion of which will be larger. On the other hand, there are less oxygen vacancies in the body of the samples grown at higher temperatures, while more surface oxygen defects will produced in this case, so the magnetistion of which will be larger. The magnetic property of pure SnO2film increased with less oxygen pressures. Furthermore, it is found that vacuum anneling would increase the magnetization of the samples for more surface Vo was protroduced. It can be concluded that Vo+and Vq is the origin of the magnetism in SnO2films.