The Magnetic Anisotropy Of Fe,Co Films And Their Temperature Dependence

In this paper,the iron films grown on Si(111)substrates and the cobalt films grown on MgO(001)and Si(100)substrates were studied.The static magnetism and dynamic magnetization process of ferromagnetic metal films was researched basing on temperature.The study of static magnetism analysis mainly based on the self-built low-temperature transport measurement system,magneto-optical system for magnetic anisotropy research of ferromagnetic iron and cobalt films and its temperature dependence.For spin dynamic,the magnetization of the above materials was studied by using the all-optical pump-time-resolved magneto-optical Kerr effect and the vector network analyzer-coplanar waveguide magnetic resonance system.The dynamic recovery of the spin precession is studied by the comparison of two kinetic methods.The intrinsic dynamics property of the magnetic ultrathin films is studied to provide a value guide for further reducing the magnetic loss of the material.Specific work includes:1.The temperature dependence of magnetic anisotropy of ultrathin Fe film with different thickness epitaxially grown on vicinal Si(111)substrate has been quantitatively investigated using the anisotropic magnetoresistance(AMR)measurements.Due to the effect of the vicinal substrate,the magnetic anisotropy is the superposition of a four-fold,a two-fold and a weakly six-fold contribution.It is found that the temperature dependence of the first-order magnetocrystalline anisotropies coefficient follows power laws of the reduced magnetization m(T)(=M(T)/M(0))being consistent with the Callen and Callen's theory.However the temperature dependence of uniaxial magnetic anisotropy(UMA)shows novel behavior that decreases roughly as a function of temperature with different power law for samples with different thickness.We also found that the six-fold magnetocrystalline anisotropy is almost invariable over a wide temperature range.Possible mechanisms leading to the different exponents are discussed.2.Co films were grown on vicinal Si(100)substrate using ultrathin p(2×2)cobalt silicide as buffer layer and its morphology and structure were researched using in-situ scanning tunneling microscope(STM)and the low energy electron diffraction(LEED).We systematically studied the magnetic property and its temperature dependence using magneto-optic Kerr effect(MOKE),anisotropy magnetoresistance(AMR)transport measurements and a superconducting quantum interference device(SQUID).The results show that there exists a~1.2-nm critical thickness of the Co film at room temperature where the ferromagnetic order occurs.The symmetry of magnetic anisotropy energy of 4.5 nm Co films shows the superposition of four-fold symmetry and a weakly uniaxial contribution.We demonstrated that the temperature dependence of both the cubic magnetocrystalline anisotropies and uniaxial magnetic anisotropy constants are proportional to the power laws of the reduced magnetization(Ms(T)/Ms(0))with different exponent being much closed to the theoretically expected one.3.Co epitaxial thin films with 2.5nm thickness were prepared on single-crystal MgO(001)substrates and annealed at different temperatures.The contribution of each interface of the Cu/Co/MgO trilayer to the in-plane magnetic anisotropy(IMA)was studied by changing interfacial coupling through annealing.We found that the magnetic anisotropy of the as-deposited one shows superposition of a two-fold symmetry with a weak four-fold contribution caused by the stress of the interface between Co/Cu.After annealing at 200?,the symmetry of magnetic anisotropy was changed from uniaxial magnetic anisotropy(UMA)into four-fold symmetry due to the significant increasing of four-fold magnetocrystalline anisotropy.When the films were annealed above 300?,the damage of the MgO/Co interface additionally decreased the IMA to isotropy.Our experimental results prove that the Co/Cu interface and the MgO/Co interface play an essential role in manipulating the four-fold and the UMA in the system.4.Finally,combined with the static magnetism analysis,we studied the spin dynamics of the film to better understand the dynamic characteristics of magnetic materials,and provide experimental and theoretical guidance for lower the energy loss of the material.The different thickness Co films were grown on MgO(001)substrates.We used the all-optical pumping technique and the vector network analysis-coplanar waveguide technology to study the magnetic dynamics of cobalt thin films.The effects of sample annealing and sample thickness on intrinsic damping factor were studied.At the same time,the static magnetism properties of the materials are analyzed by the comparison of the kinetic methods and the character of the two different methods in obtaining the intrinsic damping of the material are discussed.The results are compared and analyzed.