Reduction of spike noise in perpendicular recording media by using MnIr antiferromagnetic films

Abstract

We introduced a NiFe/antiferromagnetic–MnIr bilayer or a NiFe/MnIr/NiFe trilayer below a CoTaZr soft magnetic underlayer in perpendicular recording media as a way of controlling the magnetic domain structure of the soft magnetic underlayer, and we investigated the effect of exchange biasing on the spike noise. Samples consisting of a layer structure—NiFe (5 nm thick)/MnIr (2.5–50 nm)/NiFe (5 nm)/CoTaZr (50–200 nm)—were sputter deposited on precoated glass disks. The samples were heated with a lamp heater and cooled in a magnetic field along the radial direction of the disk. Both uniaxial and unidirectional anisotropies were induced along the magnetic field when the thickness of the MnIr layer was more than 5 nm. The first NiFe layer promoted a fcc–MnIr (111) crystalline texture, while the second NiFe layer enhanced the value of exchange-bias field by about 20%. The exchange-bias field increased from 6 to 24 Oe as the CoTaZr-layer thickness decreased from 200 to 50 nm. Many spikes along the radial direction were observed for a 100-nm-thick CoTaZr single-layer film, while no remarkable spikes were observed for a NiFe/MnIr/NiFe/CoTaZr (100 nm) film. It was found that the NiFe/MnIr/NiFe trilayer restrained the formation of domain walls in the CoTaZr layer, thereby reducing the spike noise.

Simulating a perpendicular exchange-biased structure with a partially covering nonmagnetic insertion at the FM/AFM interface

“…Fig. 3 provides normalized values of the exchange bias, the coercivity, the loop shape factor, the magnetization of minority spins biased in the direction opposite to the expected bias, and the magnetization of majority spins pinned in the expected exchange-bias direction as a function of the surface coverage p. As seen in this figure, the exchange bias is fully correlated with the number of majority spins, while the number of minority spins follows the loop shape factor, and falls into the two minima: N (1) op (min) and N (2) op(min) . The latter unexpected result may have important implications for real magnetoelectronic devices.…”

“…op (min) and N (2) op(min) near the maximized EB. The simulation was carried out for the 50 × 50 structure with the increased exchange constants J E max = 10, the optimized surface coverage level p c = 0.1, and the standard deviation of random distribution of surface roughnesses σ=1.5.…”

“…However, it can be controlled by bulk anisotropies of the FM and AFM regions. The effect was applied in perpendicular, high-capacity recording media [2,3] and spin valves [4]. In general, an exchange bias occurs due to the domain formation in the antiferromagnetic layer, which is under the influence of the out-of-plane magnetic moments of the ferromagnetic stack of layers.…”

Giant magnetic domains in amorphous SmCo thin films

“…Typical magnetic domain sizes in thin films are in the micrometer regime, although large quasi-single-domain states have been achieved by exchange coupling soft magnetic layers to a synthetic antiferromagnet heterostructure [12,13]. Here we uncover macroscopic magnetic domains in single amorphous SmCo thin films, without the use of a pinning layer.…”

Recording characteristics of perpendicular magnetic media with CoZrNb, NiFeNb, and exchange-pinned NiFeNb soft magnetic underlayers

“…Previous work has been primarily focused on eliminating domains in the SUL to obtain low spike noise PMR media. [1][2][3][4] Our study shows that domain wall control is important, but one has to consider other characteristics such as writability of the SUL for perpendicular recording media design. In addition, this is a comparative study of the recording performance of a complete PMR media structure with and without exchange-pinned SUL.…”