Study On Resonance Frequency And Physical Properties Of Magnetic Multilayer Film

The development trend of magnetic materials is small, light and thin. Under theimpetus of this trend, magnetic multilayer film materials more and more cause people’sconcern. Resonance frequency of microwave absorbing material is higher and wider inmore and more transmission device. However, it has been limited to improve the resonancefrequencies of the block magnetic materials. Theoretical and experimental research showthat magnetic material or multilayer film is expected to expand the resonance frequenciesof the corresponding block magnetic materials. However, the classical method ignores theinfluence of the quantum fluctuations. Therefore, theoretical study is not up to expectations.In order to explore the factors influencing resonance frequency of magnetic multilayer film,and to guide the application of thin film materials, it is necessary for us to make someresearch from the perspective of quantum theory. Therefore, researching the magneticproperties and thermodynamic properties of magnetic multilayer film has importantpractical significance.In the early1980s, the giant magnetoresistance effect is found in the sandwichstructure iron/chrome/iron. Soon, the giant magnetoresistance effect is also found in somemagnetic multilayer film. The giant magnetoresistance effect has played a significance rolein magnetic storage. Based on the layered film iron/chrome/iron, a ferro-anti-ferromagnetic sandwich structure Heisenberg model is put forward. Based on molecular-based magnet, anti(ferri)magnetic-anti(ferri)magnetic honeycomb structure model is alsoput forward. It’s the first time that quantum method—Spin-wave theory is used inresonance frequencies of the above two models. The magnetism parameters, includingexternal magnetic field, interlayer (intralayer) exchange coupling (anisotropy) and spinvalues are considered. The influences of various magnetism parameters of two models onresonance frequencies, energy gap, magnetization, quantum fluctuation, internal energyand specific heat are studied by use of Spin-wave theory, Holstein-Primakofftransformation and retarded the Green’s function method. For ferro-antiferro-ferromagnetic multilayer film with sandwich structure, the resultsof the study are as follows. Under certain parameters, the number of resonance frequenciesis equal to the number of the sublattices, and the signs of resonance frequencies arecorresponding to the directions of spins. The values of resonance frequencies areinfluenced by external magnetic field and surface parameters. Five magnon energy gapsexit. The surface anisotropy, exchange coupling and spin values of the system influencethe width of energy gaps. At ground state, quantum fluctuation exits and magnetizationswith the change of interlayer exchange coupling are asymmetrical in the system.Antiferromagnetic (Ferrimagnetic) interlayer exchange coupling and anisotropy have animportant impact on the quantum fluctuations. At low temperature, the magnetizations inthe ferromagnetic layers decrease with the increase of temperature. When the interlayerinteraction is ferromagnetic, the sublattice magnetizations appear a cross phenomenon.Both internal energy and specific heat increase with the rise of temperature. Theenhancements of magnetism parameters, such as external magnetic field, reduce theinternal energy and specific heat of the system.For antiferro(ferri)magnetic-antiferro(ferri)magnetic multilayer film with honeycombstructure, the results of the study are as follows. There are two resonance frequencies incertain parameters. When the external magnetic field, surface intralayer exchange coupling(anisotropy) and interlayer anisotropy are strengthened, the absolute values of theresonance frequencies increase. The spin values of the system also influence resonancefrequencies. A magnon energy gap exits in the system in certain parameters. The magnonenergy gap width increases with the increase of interlayer anisotropy, surface intralayerexchange coupling (anisotropy) and spin values. At ground state, the interlayer anisotropyweakens quantum fluctuation, however, increases magnetization. The surface intralayerexchange coupling (anisotropy) increases quantum fluctuation, however, weakensmagnetization. When temperature is fixed, the magnetizations of two sublattices are relatedto the interlayer exchange couplings and external magnetic field. The internal energy andspecific heat increase with the rise of temperature. The enhancement of any magnetismparameter reduces the internal energy and specific heat of the system.