The Study Of Perpendicular Magnetic Anisotropy In Pd/Heusler Alloy(Co₂FeAl_0.5Si_0.5,Co₂MnSi)/MgO Films

Nowadays,the spintronic device of Magnetic Random Access Memory(MRAM)based on c.urrent induced magnetic reserval(CIMS)has drawn an increasing scientific interest,in which reducing the critical current(Ic0)of magnetic reversal is one of the key isssues.The perpendicular magnetic anisotropy(PMA)and high spin polarization of the ferromagnetic layer are theoretically predicted and experimental verified to be useful for reducing the IC0.Thus,the key point is to achieve PMA behavior in the magnetic layers with the high spin polarization.In this work,the Pd/Heusler alloy layer/MgO films were prepared by magneton sputtering,in which the Co-based Heusler alloys of Co2FeAl0.5Si0.5(CFAS)and Co2MnSi(CMS)were selected as the magnetic layers.A systematic study of PMA has been carried Oout in the two series films.The main achievements are shown as below:Firstly,the effect of PMA in CFAS system on annealing temperature,magnetic layer thickness and inserted Pd layer(or bottom Ta buffer layer)has been investigated through varying the depositing conditions.The results shows that the greatest PMA can be obtained in Pd/CFAS(3.2 nm)/Mgo film annealed at 300 ?,in which the values of effective magnetic anisotropy Keff is 1.23×106 erg/cm3.Through the depth-profiling XPS analysis,it has been found that the reduction of Co,Fe at the CFAS/MgO interface can be observed during the annealing process and the inserted Pd layer can hinder the migration of oxygen to Ta layer,which both can modify the interface of CFAS/MgO and ensure the effective Co-O and Fe-0 orbital hybridation to realize PMA in Pd/CFAS(3.2 nm)/MgO film.Aiming at further increasing the ordering of Heusler alloy layer and the value of Keff,the systemtic study of PMA in CMS has been performed with a pseudo-phase diagram depicted between annealing temperature and CMS thickness for PMA realization.At the same time,the contribution of Pd/CMS and CMS/MgO interfaces to PMA in whole Pd/CMS/MgO films has been accurately evaluated.It was found that the greatest PM A can be obtained in Pd/CMS(3,4 nm)/MgO films annealed at 300 ? with the Keff value of 1.61 × 106 erg/cm3,higher than the value of CFAS system.The interfacial anisotropy Ks,MgO of 0.79 erg/cm2 at the CMS/MgO interface is larger than the Ks,Pd value of 0.26 erg/cm2 at the Pd/CMS interface,implying more contribution of the CMS/MgO interface to PMA of the whole films.Additionally,amorphous Pd/CMS interface and partially crystalline CMS/MgO interface can be observed by the high resolution transmission electron microscopy(HRTEM)analysis.Moreover,the Mn-O bonding was found to be enriched at the CMS/MgO interface with the depth-profiling XPS and STEM-EDS line scanning,which is consistent with the theoretical calculation which speculates the Mn-O bonding at the interface of CMS/MgO is helpful for realizing PMA.