Study On Perpendicular Magnetic Anisotropy Of Co-based Magnetic Multilayers

Magnetic multilayers with perpendicular magnetic anisotropy(PMA)is important for spintronic materials and it has good thermal stability and low saturation field to reduce current density for current induced magnetization reversal in the vertical magnetic nanostructures.The magnetic properties and spin polarized transport of Co/Pt,Co/Ni and CoFeB/Ni magnetic layers were studied.CoFeB/Ni based magnetic multilayer was researched for the first time.The PMA of the samples increased deeply by inserted MgO underlayer.The Co/Pt multilayers with Pt and MgO/Pt underlayer were prepared by magnetron sputtering and the PMA of the multilayers were researched by anomalous Hall effect(AHE).The results show that the sample has pretty good thermal stability and the PMA of Co/Pt multilayers was improved greatly by the additional scattering of electrons induce from the amorphous insulator-metal interface of MgO-Pt.When MgO layer thickness was 4nm,the Hall resistance(RHall)of the Co/Pt multilayer increased by 17%and the coercivity(HC)increases by 324%.Annealing effects of the MgO-added sample showed that the effective anisotropy constant(Keff)was grown by 356%.A series of Co/Ni multilayers with MgO/Pt underlayer were prepared.AHE tests showed that the magnetization reversal of the samples were very rapid,furthermore,remanence ratio of the samples reached 100%which indicated that the samples had good PMA.The results showed that the roughness of Co/Ni multilayer was greatly reduced so the PMA of the Co/Ni multilayer was enhanced greatly with the addition of MgO.The Keff of the samples had grown by 185%and 215%respectively after MgO added to the underlayer and annealing treatment.The PMA of CoFeB/Ni multilayers was dependent on the thickness of MgO,Pt,Co,CoFeB and the number of CoFeB/Ni bilayers strongly.The optimum CoFeB/Ni multilayers were obtained with Pt and MgO/Pt underlayer respectively.With the addition of MgO,the Keff was grown by 176%compared to the Pt underlayer Co/Pt multilayer and it was changed to 212%after annealing treatment.The X ray diffraction and transmission electron microscope of the samples showed that the(111)texture of the samples is enhanced with the addition of MgO which made the PMA of the multilayers increased.A structure of Pt/[Co/Ni]2/Au/[Co/Pt]N with perpendicular magnetic anisotropy was prepared successfully by magnetron sputtering technique.The magnetic properties dependence of Au thicknesses and[Co/Pt]layer repetition number was studied.The results showed that when the[Co/Pt]layer repetition number was 4,the strongest coupling among the samples occurs when the Au layer was 3nm for its largest Hall voltage and large switching field plateau.The Hall loop of the sample had obvious perpendicular magnetic anisotropy.The magnetoresistance of Pt/[Co/Ni]2/Au(tAu)/[Co/Pt]4 had vibration behaviour due to the Ruderman-Kittel-Kasuya-Yosida interaction with the increase of tAu.As the thickness of the Au spacer is determined to be 3nm,the study of dependence of Co/Pt layer repetition number to the magnetic properties showed that the N has significant influence to the magnetoresistance of the multilayer films.When N was 5,the MR of the sample had the maximum value and the optimum sample was structured as Pt(4)/[CO(0.2)/Ni(0.4)]2/Co(0.2)/Au(3)/[CO(0.4)/Pt(2.0)]5/Pt(0.5)(unit:nm).It has obvious perpendicular magnetic anisotropy features and large switching field plateau and the integration with device can be studied furtherly.