| In the era of information and technology’s rapid development,how to achieve information quickly and accurately should be solved.An emerging direction about sensor aim at discovering novel applications due to significant means of information acquisition and conversion in the research.The magnetic sensors can measure the location,direction and other physical quantities by sensing the magnetic field strength.The well-known fact that dissimilar types of magnetic sensors have been used for industrial production,such as Hall effect sensors,anisotropic magnetoresistance(AMR)effect sensors and giant magnetoresistance(GMR)effect sensors.Though some drawbacks among them,the Hall effect sensors have large power consumption and poor linearity.Narrow linear range and complicated preparation existed in AMR sensors.The GMR sensors also have the defects of narrow linear range and low sensitivity.Compared to these types of sensors,the tunneling magnetoresistance effect(TMR)magnetic sensors have characteristics of better temperature stability,linearity and sensitivity,lower power consumption,in the meanwhile these sensors can be applied in speed and angle as well as small displacement measurement and other aspects.However,the narrower linear range limit the application of the high field linear sensors which need magnetic field response achieved at Tesla,such as magnetic levitating train and high field positioning measurements.In this paper,we design and fabricate the magnetic tunnel junction by choosing the L10-FePt with large coercivity and high squareness ratio as reference layer,soft magnetic material with in-plane anisotropy as free layer.An approach of making a high field linear magnetic field response is to use a sandwich structure with a reference layer having high perpendicular magnetic anisotropy and an in-plane anisotropy free layer.The main contents are as follows:1.Preparation and optimization of L10-FePt films.FePt films were deposited on the Sr Ti O3(001)substrate at high temperature,and the L10-FePt films with high perpendicular anisotropy was obtained.The maximum coercive force was 2 T and rectangular ratio was 0.99.By reducing the deposition temperature to 450℃,the surface was continuous and smooth which meet the preparation requirements of magnetic tunnel junctions.Simultaneously,relatively high perpendicular anisotropy L10-FePt films with coercive force of 7 k Oe,rectangular ratio of 0.9 and a small surface roughness was prepared on the MgO(001)substrate by inserting a Pt buffer layer.These optimized materials laid the foundation on the preparation of magnetic tunnel junctions.2.Study on magnetoresistance effect and linear response of Sr Ti O3/L10-FePt/ Zn O/FePt multilayer structure.The sandwich structure L10-FePt/Zn O/FePt with L10-FePt reference layer having perpendicular magnetic anisotropy and FePt in-plane magnetic anisotropy free layer was prepared on Sr Ti O3(001)substrate.The magnetoresistance effect and linear response have been studied particularly.The magnetic resistance values of 0.69% and 0.77% were obtained at 300 K and 150 K,respectively。The TMR-H linear range is ±200 Oe at room temperature,and widened to ±1000 Oe at 150 K.3.Study on magnetoresistance effect and linear response of Pt/MgO/Pt/ L10-FePt/Zn O/Fe/Pt multilayer structure.The L10-FePt/Zn O/Fe sandwich structure was prepared on Mg O(001)substrate,in which L10-FePt was reference layer with perpendicular anisotropy and Fe was free layer with the in-plane anisotropy.Focusing on the relationship among the structure,magnetic properties and magnetoresistance effect.The self-pinning effect from L10-FePt is better and less coupling effect derived from the ferromagnetic layers to achieve the magnetic moment reversal freely.The MR values of 0.5% and 1.2% were obtained at 300 K and 10 K,respectively.The linear MR response and fine reversibility were observed in this sensor between +5 k Oe and-5 k Oe at room temperature.In short,the magnetic tunnel junctions in which magnetic moment of ferromagnetic layers are perpendicular can be designed and prepared on the L10-FePt thin films with high coercivity and large rectangular.Linear magnetoresistance is observed in this sensor in a large range between +5 k Oe and-5 k Oe at 300 K.These L10-FePt based sensors are significant for the simplification of preparation,the expansion of linear range and self-pinning of the bttom ferromagnetism layer,so it can provide experimental basis and reference for realizing a certain application about magnetic tunnel junctions on high field linear magnetic sensors. |
