Design and Synthesis of an Artificial Perpendicular Hard Ferrimagnet with High Thermal and Magnetic Field Stabilities

Jun Lu,Jianhua Zhao,Jian Liu,Jianbai Xia,Xupeng Zhao,Siwei Mao,Peng Xiong,Xiaolei Wang

doi:10.1038/s41598-017-16761-z

Abstract

It is of great fundamental and practical interest to develop effective means of modulating the magnetic hystereses of magnetic materials and their heterostructures. A notable example is the exchange bias (EB) effect between an antiferromagnet or ferrimagnet and a ferromagnet, which has been widely employed to manipulate magnetic anisotropy in spintronic devices and artificial magnets. Here, we report the design, synthesis and characterization of a synthetic perpendicularly-magnetized ferrimagnet based on [Mn2.9Ga/Co2MnSi]n superlattices, which attains thermal stability above 400 K and a coercive field up to 45 kOe through a mechanism of magnetic compensation. The structure is incorporated into a prototype Heusler alloy and MgO barrier based magnetic tunnel junction, which demonstrates high dynamic range linear field responses and an unusual in-plane EB effect. With increasing temperature, the coercive field reaches beyond 70 kOe at 400 K in this device due to the increasing degree of magnetic moment compensation in the superlattice. The results demonstrate that the compensation mechanism can be utilized to achieve simultaneous thermal robustness and high coercivity in realistic spintronic devices.

Highlights

FIM/FM bilayers including SmAl2/Sm0.974Gd0.026Al27, DyCo5/Ta/Fe76Gd249, [Co/Ni]n/TbCo10, TbFe/[Co/Pt]n11
Where K1 is the perpendicular anisotropy of the perpendicular hard magnet FM1, K2 is the in-plane uniaxial anisotropy of the soft magnet FM2, M1 (M2) and t1 (t2) are the saturation magnetization and thickness of FM1 (FM2) respectively, θ1 (θ2) is the angle between M1 (M2) and the film normal, and Jex is the exchange coupling constant between M1 and M2
As is evidenced in intrinsic FIMs such as TbxCo1−x, DyCo5, and Sm0.972Gd0.028Al2 etc., magnetic compensation is a most important condition for large exchange bias effect in FM/FIM multilayers; we have adopted this concept in the design and synthesis of an artificial perpendicularly-magnetized FIM

Summary

Introduction

FIM/FM bilayers including SmAl2/Sm0.974Gd0.026Al27, DyCo5/Ta/Fe76Gd249, [Co/Ni]n/TbCo10, TbFe/[Co/Pt]n11. We realized a thermally robust, perpendicular hard artificial FIM based on perpendicularly-magnetized, AFM-coupled [Mn2.9Ga/Co2MnSi]n superlattices (we describe the form of Mn2.9Ga as MnGa for simplicity from the outset). An ultralow damping constant of 0.008 was determined from optical pump-probe measurement[25], and a spin polarization of 58% as well as a Curie temperature of 730 K was observed[26,27] These features make it an attractive candidate for modern magnetic information storage devices at sub-10 nm nodes. By reducing the Co2MnSi thickness to 1 nm, we successfully realized AFM-coupled [MnGa/Co2MnSi]n superlattices with full PMA, which presents a model system of perpendicularly-magnetized hard FIM with near zero net magnetization at tunable temperatures. Curie temperatures of the AFM-coupled FM layers, the [MnGa/Co2MnSi]n superlattices have the potential for achieving a compensation temperature much higher than 400 K. The results demonstrate that the compensation mechanism can be utilized to achieve simultaneous thermal robustness and high coercivity in realistic spintronic devices

Methods

Results

Conclusion