Nanoscale Control Of Perpendicular Magnetic Anisotropy In Co Film Via Electric Driven Oxygen Migration

The rapid development of information technology has provided a lot of convenience.In the field of information storage,the traditional non-volatile memory can't meet the present day requirements i.e.high speed,long life,large capacity,low power consumption and easy operation.Thus the development of new storage technology has very important strategic significance for China's microelectronics industry.MRAM,which is based on magnetic materials,is considered to be the main candidate for the next generation memory.It records“0”and“1”using the difference in magnetoresistance caused by the different magnetization directions.Magnetization direction can be controlled in a variety of ways but its control by the ion transport is considered to be the most efficient way.At present,most of research of the electric field control ion transport is focused on the regulation of macroscopic magnetic properties,such as coercivity and saturation magnetization,and little work is done about the regulation of microscopic magnetic properties.Investigating the nano-scale electric field control of ion transport not only regulates the magnetization state of micro-scale materials,but also improves the storage density of MRAM.In this research,regulation of magnetic domain changes in microscopic regions has been carried out by nanoscale electric fields:High-quality Pt?4nm?/Co?0.6nm?/GdO_x?5nm?films are fabricated by magnetron sputtering system.Hysteresis loop measurements confirm the film's perpendicular anisotropy.The macroscopic transport tests confirm the reversible movement of oxygen ions of GdO_x under positive and negative electric field.Electric field control magnetism at the nanoscale is studied using conductive atomic force microscopy?CAFM?and magnetic force microscopy?MFM?techniques.Initially,electric field control the transport of oxygen ion in the Gd O_x thin film,afterwards the adjacent Co layer thin film showed the reversible control of the magnetic domain contrast changes.This result is quantified by phase value and it reveals that the phase value can change reversibly.Meanwhile,the current density is studied.It is also found that where the current density is greater,the change in the phase value of the magnetic domain is also larger.In order to verify the previous study,the current density is gradually increased by cyclically applying a small voltage.In this process,we not only verify the relationship between the previously estimated current density and the magnetic domain contrast change ratio,but also find that there is an intermediate state in the influence of the direction.It is an auxiliary effect on the perpendicular anisotropy when the oxygen ions are transported to the interface.The results of the development of high-density MRAM are of great significance.In addition,we perform a small part of the research work on NiCoMnAl alloys.Ni_42.8Co_7.7Mn_38.8Al_10.70.7 alloy samples are prepared by arc melting.Through the results of the thermomagnetic curve and the isothermal magnetization curve,it can be found that the phase transition temperature of the component alloy is near room temperature,and a large change in magnetization occurs.Magnetic transmission measurements reveal that the magnetoresistance varied by about 45%at a magnetic field of 90 kOe around room temperature.The magnetostrictive strain measurements show that the alloy sample shrinks to500 ppm at a magnetic field of 90 kOe.In addition,the magnetic microscopy?MFM?is used to study the surface topography and magnetic domain structure of alloy samples under the magnetic field.As a result,it is found that the magnetic field response of the surface topography and magnetic domain changes is consistent with the macroscopic magnetization curve,and there is also a hysteresis effect.These results explain the magnetic alloy's changing behavior under magnetic field,and provide a good reference for the study of magnetic alloys.