Material Optimization And Linear Response Study Of L1₀-FePt?CoPt? Based Magnetic Resistance Sensor

In diversified information age,access and conversion of information is vital.Magnetic sensors play a leading role in this aspect and is the core of the information science.The conventional magnetic sensor which based on Hall Effect and anisotropic magnetoresistance?AMR?effect has a large volume,low sensitivity,narrow linear range and other shortcomings,so it is difficult to achieve a unity of high sensitivity and high integration.Currently,new type of magnetic sensors which based on the giant magnetoresistance?GMR?effect and tunneling magnetoresistance?TMR?effect overcome these shortcomings and have a good linear response,high sensitivity,good thermal stability and frequency response and so on.They are gradually replacing the traditional magnetic sensors in the information technology,automotive electronics,mechatronics control and other areas.However,in the magnetic sensor device which needs for a strong induction field,even to the level of Tesla,this type of magnetic sensor is difficult to be widely applied.Accordingly,we designed the anisotropic hard magnetic material having a large vertical to be used as a reference layer and the in-plane anisotropy soft magnetic material to be used as the free layer of the cell,so that the magnetic moment of two ferromagnetic layers formed naturally vertical structure and obtained magnetoresistance linear response under external magnetic field.The performance of L1₀-CoPt and L1₀-FePt which were used as a reference layer will have a great impact on magnetoresistance and linear output range of magnetic multilayer linear sensors,so in the first part of this paper,the structure,magnetism and morphology of L1₀-CoPt and L1₀-FePt were mainly studied.By optimizing the annealing conditions,Ag?50nm?/CoPt?20nm?film having a larger coercivity,high squareness ratio and smooth surface was prepared by high vacuum annealing 60 min at 450?.Its coercive force was about 14,000 Oe,the squareness ratio Mr/Ms was 0.92,and switching field distribution?SFD?in the direction which was perpendicular to the film plane was 0.36.At the same time,we also optimized the thickness of reference layer FePt and buffer layerPt and online annealing time during the preparation of L1₀-FePt.ThePt?4nm?/FePt?20nm?film having perpendicular anisotropy,a large coercivity,high squareness ratio and small roughness can be obtained by online annealing 2h at 450?.Compared to L1₀-CoPt material,L1₀-FePt material has a larger coercive force and higher magnetic anisotropy energy,so it was used as a reference layer in magnetic multilayer film layer.In the second part of this paper,we prepared L1₀-FePt-based magnetic multilayer samples with the structure ofPt/FePt/X/Fe on a single crystal Mg O?001?by high vacuum magnetron sputtering device,and studied how Cu and Zn O used as intermediate layer has effect on multilayer film magnetoresistance and MR-H linear output range.As the magnetic multilayer films with Cu intermediate layer in the 10 K,the MR ratio can reach 1.6%,the MR-H linear output can be achieved in the external magnetic field range-0.6T to 1T.If Zn O barrier was used as intermediate layer,the ratio MR can reach 0.5%,and in the range-0.5T to 0.5T,the MR-H linear output can be achieved at 300 K.In short,by optimizing experimental conditions,we prepared L1₀-CoPt and L1₀-FePt film with a larger coercivity,high squareness ratio and a smooth surface.Moreover,L1₀-FePt based magnetic multilayer films with different intermediate layers have produced a magnetoresistance effect.Although the resulting MR value is relatively small,it still lays the foundation for the application of magnetic multilayer linear sensor.