The Study Of Magnetic Structure,Exchange Bias And Transport Properties On FePt₃ Films

As one of the key elements in spintronics,the magnetic multilayer thin films have complex exchange coupling and electronic transporting behavior and abundant physical connotations.FePt3 is an antiferromagnet,displaying an interesting behavior at low temperature:it reorients the spin wave propagation direction.This transition has consequences that make FePt3 an attractive system,namely in the field of exchange bias interaction studies.The thesis mainly includes the following four aspects:1.The epitaxial FePt3 films with varying degrees of chemical order were grown by Pulsed Laser Deposition at different temperatures,after which the lattice structure of samples were characterized by X-Ray diffraction spectra.The Magnetic properties of samples have been measured and the dependence of exchange bias on temperature and order parameter has been investigated.It was found that all samples show considerable negative exchange bias below a temperature of 160K,and the values decrease with the increasing order parameter.Our study suggests that chemical order in FePt3 can be effectively used to tailor the exchange bias effect with a system containing only one material species.The approach via tailoring magnetic composition by chemical order offers the possibility to concentrate on purely magnetic effects responsible for the occurrence of the EB effect.2.Using the first-principles calculations to study the phase competition of different magnetic order in FePt3,by introducing chemical-disordered,it can be found that both Fe-rich system and Pt-rich system demonstrate an coincident relationships with standard stoichiometry of FePt3.In other words,the phase of Q2 will be induced by introducing chemical-disordered,and exists stably,and the two phases of Q1 and Q2 will complete with each other in a certain degree of order.While,by introducing uniform strain and quadrilateral distortion strain,it can be found that the phase of AFM-Q2 will also be formed and exists stably with the strain increasing evenly.Increasing the ration of c and a,may also induces to form Q2 phase,while FM phase will not be impacted strongly.The conclusion can be indicated that FePt3 with highly ordered has tremendous bias field through analyzing the positive and negative energy difference of magnetic moment of FM phase by introduced with chemical-disordered,which can also be verified by the results in chapter 3.3.We have researched the magnetic and exchange bias effect of ordered/disordered double-layer film of FePt3.Since there has phase competition of magnetic ordering in antiferromagnetic layer by analyzing arrangement of magnetic moment at the antiferromagnetic interface,we propose a theory that there are two mechanisms of indirect pinning model and M-B model presenting in exchange bias effect of double-layer film of FePt3.It is indicated that Q2 phase has not been restrained completely in double-layer film of antiferromagnetic layer of FePt3(100),which means there exists the Q2 phase with an uncompensated spin arrangement in antiferromagnetic layer,and it can be validated by the results of first-principles calculations in the exchange bias filed below 90K.4.By investigating the R-T curves in FePt3,it indicates that the electrical resistivity of samples are manifested as phono-electron scattering mechanism,T<50K,??Ts,which is shown as electron-phonon scattering,and T>50K,??T2,it's shown as single magneton scattering,and around 170K,the difference are contributed by antiferromagnetic phase.According to the researches of MR,at high temperature,the magnetoresistance of negative magnetic effect with spin scattering are dominant,while,it's anisotropy taking the dominant role at low temperature range,and the positive magnetoresistance effect derived from the effect of Lorentz force magnetoresistance in low temperature measurement of I?H.By investigating the relationship between negative magnetoresistance with spin scattering and temperature,it indicates that the absolute value of magnetoresistance of FePt3 is not increasing with temperature although it is metal,while the special variation of magnetoresistance is contributed by antiferromagnetic.