Study On Fabrication And Magnetoelectronic Properties Of Perpendicularly Magnetized Rare-earth Transition Metal Soft/Hard Structures

The magnetic random-access memory(MRAM)with widely practical applications,based on magnetic tunnel junction(MTJ),is expected to replace traditional static and dynamic random-access memory and promises to be the next-generation universal memory.Meanwhile,amorphous heavy rare-earth transition metal(RE-TM)alloy films with perpendicular magnetic anisotropy(PMA)have been widely used in MRAM.Among them,GdFeCo and TbFeCo films,the conventional magneto-optical storage media,have been attracting interest in ultra-fast-rate recording technology and magneto-electronic devices.It is of great significance to study their fabrication methods and perpendicular magnetic properties.We systemically studied fabrication and magnetic properties of RE-TM(Gd,Tb)-FeCo films and soft/hard heterostructures.The main research contents and conclusions of this thesis are as follows:Firstly,a series of amorphous GdFeCo films were fabricated by RF magnetron sputtering using a composite target consisting of FeCo alloy disk and Gd chips.The experimental results show that the magnetic properties of the films are found to be strongly related to sputtering power.A shift of magnetic configuration in the film from FeCo-rich to Gd-rich side is observed with increasing the sputtering power,which could be confirmed by thermomagnetic measurements.Secondly,sample of Si/Ta/MgO/GdFeCo/MgO multilayer films were fabricated.The structures can apply an appropriate electric field by introducing MgO dielectric layers.The effect of electric field on the magnetoelectric properties of thin films was studied by using the magneto-optical Kerr effect.The results show that the negative bias can significantly adjust the coercivity of the films.It could be applied to electric-field control of magnetization by improvement of the film structures.Then,double-layer GdFeCo antiferromagnetic coupling structures were fabricated.The magnetoelectric properties of the film are related to sputtering process.The results show that the magnetization of the two layers of GdFeCo is equal but opposite to each other in the vicinity of the zero field,and multiple magnetization reversals are realized in the high field.It is of great value for the study of antiferromagnetic coupling structures.Finally,magnetic heterostructures consisting of magnetically soft GdFeCo and hard TbFeCo alloy were fabricated.The influence of the thickness of GdFeCo on the magnetoelectric properties of the magnetic heterostructures was investigated.The results show that exchange-spring and sharp switching in a step-by-step fashion were observed in the heterostructures with increasing GdFeCo thickness.A perpendicular exchange bias field of several hundred Oersteds is observed.The perpendicular exchange energy is derived to be in the range of 0.18-0.30 erg/cm~2.The exchange energy is shown to increase with the thickness of GdFeCo layer,which can be attributed to the enhanced perpendicular anisotropy of GdFeCo layer in our experimental range.The magnetic heterostructures provide a good opportunity to design composite systems with desired properties by combining individual material with dissimilar properties.