Perpendicular magnetic anisotropy and interlayer exchange coupling in heterostructures of NiO and [CoFe/Pt] _n multilayers

Abstract

PACS 75.30.Gw, 75.70.Cn Antiferromagnetic (AF) layer thickness and the annealing temperature dependences of perpendicular magnetic anisotropy (PMA) in the [CoFe/Pt] n multilayers exchange-coupled by NiO pinning layers at the top and bottom interfaces were investigated. Also we confirmed that the interlayer exchange coupling (IEC) at room temperature (RT) as a function of NiO thickness with a period of two monolayers existed.1 Introduction To achieve the truly next generation device for applying a magnetic random access memory (MRAM) using the magnetic tunnel junction (MTJ), all using ferromagnetic materials should be patterned into sub-micron elements. There are existed two hurdles in the conventional MTJ device, such as; a magnetization curling occurs at the edge of the film and in the vortex magnetization, and an anomalous switching depends on the shape of the in-plane MTJ. There are also caused by switching field fluctuations, which occur at the film edge when using an in-plane MTJ. On the other hand, perpendicular magnetic anisotropy (PMA) films have a low saturation magnetization, preventing any magnetization curling at the film edge [1]. Therefore, a MTJ with an aspect ratio of L(length)/W(width)=1 can be realized using perpendicular magnetization [2,3].We studied antiferromagnetic (AF) layer thickness and the annealing temperature dependences of perpendicular magnetic anisotropy in the [CoFe/Pt] N multilayers exchange-coupled by NiO pinning layers at the top and bottom interfaces. Also, the characteristics of the interlayer exchange coupling (IEC) across of insulating AF spacer (NiO) in heterostructures of type [Pt/CoFe] n AF/[CoFe/Pt] n was investigated.