Study Of Fabrication And Magnetic Properties Of CoFe-based Alloy Thin Films With Perpendicular Magnetic Anisotropy

With the development of information technology,there are higher requirements on information storage technology.Increasing the storage density and storage speed and reducing the power consumption have become one of the most active fields of information technology.Based on Magnetic Tunnelling Junction?MTJ?,Magnetic Random Access Memory?MRAM?promises to be the next-generation universal memory thanks to the low power consumption,large storage density and fast storage speed.Co₂FeAl?CFA?and GdFeCo soft magnetic thin films have large perpendicular magnetic anisotropy.In addition,CFA alloy thin films have high spin polarization and low damping factor.The speed of magnetization reversal of GdFeCo thin films can be up to picosecond and femtosecond.So they are widely used in MRAM.Investigation on perpendicular magnetic anisotropy of CFA and GdFeCo thin films is of great significance as for its key role in MTJs.In this paper,we systemically studied fabrication and magnetic properties of CoFe-based alloy thin films with perpendicular magnetic anisotropy,including:Firstly,25-nm-thick CFA alloy films were prepared by magnetron sputtering at different powers and annealed at different temperatures.The influence of sputtering power and annealing temperature on the magnetic properties of CFA films was investigated by vibrating sample magnetometer?VSM?and X-ray diffraction?XRD?,respectively.The results show that the as-deposited film sputtered at low power is weak-magnetic.Then the alloy annealed at 300?exhbits magnetic anisotropy.In contrast,the as-deposited film sputtered at high power is ferromagnetic and exhbits uniaxial magnetic anisotropy.Moreover,It is found that the in-plane magnetic anisotropy disappears when the samples were annealed at 700?.X-ray diffraction measurements reveal the grain size of the films increases with the annealing temperature.The coercivity is found to increase with the annealing temperature,which is accordance with the grown nanocrystalline grain size.Secondly,the films with the perpendicular magnetic anisotropy were realized in the Pd/Co2FeAl/MgO structure.A series of Pd/Co2FeAl/MgO films were prepared and annealed at 200-450?in vacuum.The effects of annealing temperature,magnetic layer thickness,Pd/CFA and CFA/MgO interface on the perpendicular magnetic anisotropy of the films were studied by VSM and anomalous Hall effect method.The results show that the Pd/CFA/MgO thin films annead at 250-400?have perpendicular magnetic anisotropy.The films annealed at 300?or 350?have better perpendicular magnetic anisotropy.When the films are annealed at 300?or 350?,the perpendicular CFA thickness range can be 3-5.5 nm and the effective magnetic anisotropy can reach2×10⁶ erg/cm³.In addition,it is found that the interface between Pd/CFA and CFA/MgO has positive contributions to the perpendicular magnetic anisotropy of Pd/CFA/MgO thin films,where Pd/CFA interface plays a major role in the contribution of thin film PMA.At last,a series of GdFeCo thin films with a thickness of 100 nm were prepared by DC magnetron sputtering at different power using a composite target.Because of increase of the content of Gd with the increasing sputtering power,the easy axis of the GdFeCo film changes from horizontal direction to perpendicular direction.In order to study the thermal stability of thin films,100-nm-thick Gd-rich GdFeCo thin films were annealed at different temperatures.The magnetic,optical and electrical properties of the films were measured.The films annealed at 200?also keep PMA with the Gd-rich state,indicating that the films have good thermal stability.A series of GdFeCo thin films with thinner thickness were successfully prepared by RF magnetron sputtering instead of DC magnetron sputtering.The magnetic properties were also tunable.