Magnetic domain structures and spin switching properties in submicron size synthetic antiferromagnets (SyAFs), Co90Fe10/Ru/Co90Fe10 with aspect ratio (k) of 1, have been studied by using magnetic force microscope (MFM) image under an external magnetic field and by a focused magneto-optic Kerr effect system. It is found that SyAF with k=1 shows the single domain structure during magnetization reversal, and exhibits size- and shape-independent spin switching field.

In this paper, we report the experimental results for investigation of both switching fields and magnetic domain structure for micron to submicron size SyAF elements.

The arrays of the synthetic antiferromagnetic (SyAF) patterned bits consisting of Co90Fe10 (t1nm)/Ru (d nm)/Co90Fe10 (t2 nm) were successfully fabricated with micron to submicron sizes and different aspect ratios. Magnetization switching field Hsw and magnetic domain structure were investigated using magneto-optical Kerr effect and magnetic force microscopy (MFM), respectively. It was demonstrated that the strongly AF-coupled SyAF with aspect ratio k=1 creates size-independent Hsw down to submicron sizes fabricated, which is understood by zero demagnetization field for k=1 and single domain structure, observed by MFM. The size-independent switching field demonstrates the predominance of the SyAF for spintronics devices, requiring a low switching field and stabilized single domain structure for small bit sizes such as ultrahigh density magnetic random access memories and spin transistors.

Arrays of the synthetic antiferromagnetic (SyAF) patterned bits were successfully fabricated with micron to submicron sizes. Magnetic domain structure was investigated using magnetic force microscopy (MFM) for the SyAF bits as well as monolayer bits. MFM image of Co90Fe10(10 nm)/Ru(0.6 nm)/Co90Fe10(6 nm) SyAF bits demonstrates single domain structure for even a small aspect ratio of 1, while the 10 nm Co90Fe10 monolayer bits showed multi-domain structure for the aspect ratios below 2. This result indicates the predominance of the SyAF for ultrahigh bit density magnetic random access memory devices, because the bits with aspect ratio of 1 possessing single domain structure can provide size-independent switching field.

Switching characteristics and magnetic domain structures in submicron size synthetic antiferromagnets (SyAF), Co90Fe10/Ru/Co90Fe10 have been studied. Submicron size elements with well defined geometry were prepared by electron beam lithography and argon ion milling for SyAFs and Co90Fe10 monolayers deposited by an ultrahigh vacuum sputtering system. Hysteresis loops were obtained by a focused magneto-optic Kerr effect (MOKE) system and magnetic images in the remanent state were observed by magnetic force microscopy (MFM). We found that the MFM images of SyAF exhibit a single domain structure even in the case of aspect ratio of 1, and there is an optimum ferromagnetic film thickness at which SyAF can obtain a single domain structure with such a low aspect ratio. The MOKE results show that the switching field is dependent on the element width and aspect ratio.

The effect of Ga addition on the increase of coercivity of HDDR-treated Nd–Fe–B powders was investigated. The Ga addition suppresses grain growth and may decrease the region where magnetocrystalline anisotropy is reduced. In addition, a heat treatment in which the hydrogen pressure was decreased in steps during the recombination reaction resulted in good magnetic properties of Br=1.44T, jHc=0.97MAm−1 and (BH)max=308kJm−3.

The magnetic properties of Nd12.2Fe81.8B6.0 alloys processed using a new HDDR (hydrogenation disproportionation desorption recombination) treatment were investigated. This newly proposed HDDR treatment is a combination of heat treatments at hydrogen pressures close to the recombination pressure of the Nd2Fe14B compound, in both the disproportionation and recombination stages. In other words, this new treatment is a combination of the l-HD (heating in a low H2 pressure during the hydrogenation disproportionation stage), and s-DR (heating in Ar or in a relatively high pressure of hydrogen, at the start of recombination) treatments. In this investigation, the influence of the s-DR conditions on the magnetic properties of anisotropic Nd–Fe–B HDDR-treated powders, were investigated. It was found that an s-DR treatment in which the hydrogen pressure was decreased in steps from 0.1 MPa to 0.5 kPa, enhanced the remanence (1.45 T) and anisotropy (Br/Js=0.94). The rate at which the hydrogen pressure decreases to 6 kPa during s-DR is also considered to be an important factor in obtaining both a high remanence and a high coercivity. In addition, the coercivity was found to increase after an s-DR treatment in which the temperature was decreased in a step by step manner.