http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

Ferromagnetic materials exhibit intrinsic `easy' and `hard' directions of the magnetization. This magnetic anisotropy is, from both a technological and fundamental viewpoint one of the most important properties of magnetic materials. The magnetic anisotropy in metallic magnetic multilayers forms the subject of this review article. As individual layers in a multilayer stack become thinner, the role of interfaces and surfaces may dominate that of the bulk: this is the case in many magnetic multilayers, where a perpendicular interface contribution to the magnetic anisotropy is capable of rotating the easy magnetization direction from in the film plane to perpendicular to the film plane. In this review, we show that the (in-plane) volume and (perpendicular) interface contribution to the magnetic anisotropy have been separated into terms related to mechanical stresses, crystallographic structure and the planar shape of the films. In addition, the effect of roughness, often inherent to the deposition techniques used, has been addressed theoretically. Several techniques to prepare multilayers and to characterize their growth as well as methods to determine the magnetic anisotropy are discussed. A comprehensive survey of experimental studies on the perpendicular magnetic anisotropy in metallic multilayers containing Fe, Co or Ni is presented and commented on. Two major subjects of this review are the extrinsic effects of strain, roughness and interdiffusion and the intrinsic effect of the crystallographic orientation on the magnetic anisotropy. Both effects are investigated with the help of some dedicated experimental studies. The results of the orientational dependence studies are compared with ab initio calculations. Finally, the perpendicular surface anisotropy and the in-plane step anisotropy are discussed.

https://iopscience.iop.org/article/10.1088/0034-4885/59/11/002/pdf

Magnetic anisotropy in metallic multilayers

In recent years, the stability of recorded data against thermal decay has become an important criterion for judging the performance of magnetic recording systems. Continued growth of storage densities in the presence of thermally activated behaviour, often called the `superparamagnetic effect', requires new innovations in the recording system in general, and the recording media, in particular. This paper reviews some of the recent advances in recording media (e.g. oriented and antiferromagnetically coupled media) that have helped magnetic recording to maintain the areal density growth rate. However, more innovations and novel architectures are needed for the solutions of tomorrow. Among the more promising media approaches, which are discussed in this paper, are perpendicular, patterned and self-assembled nanoparticle media. Additionally, thermally assisted recording is also reviewed as it combines good writeability with high thermal stability.

http://iopscience.iop.org/article/10.1088/0022-3727/35/19/201/pdf

Magnetic recording: advancing into the future

Perpendicular recording technology has recently been introduced in hard disk drives for computer and consumer electronics applications. Although conceptualized in the late 1970s, making a product with perpendicular recording that has competing performance, reliability, and price advantage over the prevalent longitudinal recording technology has taken about three decades. One reason for the late entry of perpendicular recording is that the longitudinal recording technology was quite successful in overcoming many of its problems and in staying competitive. Other reasons are the risks, problems, and investment needed in making a successful transition to perpendicular recording technology. Iwasaki and co-workers came up with many inventions in the late 1970s, such as single-pole head, CoCr alloy media with a perpendicular anisotropy, and recording media with soft magnetic underlayers [S. Iwasaki and K. Takemura, IEEE Trans. Magn. 11, 1173 (1975); S. Iwasaki and Y. Nakamura, IEEE Trans. Magn. 14, 436 (1978); S...

Perpendicular recording media for hard disk drives

(1993). Ultrathin metallic magnetic films: magnetic anisotropies and exchange interactions. Advances in Physics: Vol. 42, No. 5, pp. 523-639.

Ultrathin metallic magnetic films: magnetic anisotropies and exchange interactions

Magnetic and structural properties of Co/Pt multilayers

Coupled granular/continuous medium for thermally stable perpendicular magnetic recording

A laminated magnetic recording medium for data storage has an antiferromagnetically coupled (AFC) layer and a single ferromagnetic layer spaced apart by a nonferromagnetic spacer layer. The AFC layer is formed as two ferromagnetic films antiferromagnetically coupled together across an antiferromagnetically coupling film that has a composition and thickness to induce antiferromagnetic coupling. In each of the two remanent magnetic states, the magnetic moments of the two antiferromagnetically coupled films in the AFC layer are oriented antiparallel, and the magnetic moment of the single ferromagnetic layer and the greater-moment ferromagnetic film of the AFC layer are oriented parallel. The nonferromagnetic spacer layer between the AFC layer and the single ferromagnetic layer has a composition and thickness to prevent antiferromagnetic exchange coupling. The laminated medium has improved thermal stability and reduced intrinsic media noise.

Laminated magnetic recording media with antiferromagnetically coupled layer as one of the individual magnetic layers in the laminate

The thermal stability of coupled granular/continuous (CGC) perpendicular media is supported by fundamental modeling and experimental results, including spin-stand testing. By incorporating the interlayer exchange coupling into the model, the simulation result suggests that the CGC structure is capable of achieving the energy barrier of K/sub u/V/k/sub B/T required for 1 Tbit/in/sup 2/ recording density. To demonstrate the CGC approach, we investigate a new class of CGC perpendicular media consisting of a Pt-rich CoPtCr layer with poor Co-Cr phase segregation and a thin Pt layer. The addition of these layers improves the nucleation field of the CoCr/sub 18/Pt/sub 12/ medium from +420 to -600 Oe and the thermal decay of the output is reduced from 2.23% to 0.10% per decade. Unity squareness was obtained by using a thin Pt capping layer and resulted in a small decay rate of 0.21% per decade. The new CGC media showed no degradation of SNR compared to the base granular medium. Similar to CGC media utilizing a multilayer capping structure, the CGC medium with a Pt-rich CoPtCr or Pt capping structure improved the thermal stability without compromising SNR. The simplicity of these new CGC structures also greatly simplifies the deposition process.

Thermally stable CGC perpendicular recording media with Pt-rich CoPtCr and thin Pt layers

Co/Pt multilayers composed of 0.3-nm Co and 1-nm Pt layers were prepared by e-beam evaporation from Co and Pt sources. These Co/Pt multilayers with a total film thickness of 20-30 nm have a large perpendicular magnetic anisotropy, a perpendicular hysteresis loop with a saturated remanence, a coercivity of about 1.8 kOe, and a Curie temperature of about 300 degrees C. They are structurally stable enough for thermomagnetic magnetooptical recording. Moreover, these Co/Pt multilayers are corrosion resistant and have enhanced Kerr rotation at short wavelengths. On a disk of 15*(Co(0.32 nm)/Pt(1.15 nm)) multilayer enhanced with 80-nm silicon nitride, a CNR (carrier-to-noise ratio) of 59 dB was achieved with a reading laser ( lambda =820 nm) power of 1 mW for a 2-MHz carrier at 10 m/s, and 64 dB with 3-mW read power for a 2.5-MHz carrier at 20 m/s. It is concluded that these Co/Pt multilayers are very promising as magnetooptical recording materials. >

Hoa Van Do

Papers

Magnetic and structural properties of Co/Pt multilayers

Coupled granular/continuous medium for thermally stable perpendicular magnetic recording

Laminated magnetic recording media with antiferromagnetically coupled layer as one of the individual magnetic layers in the laminate

Thermally stable CGC perpendicular recording media with Pt-rich CoPtCr and thin Pt layers

Magneto-optical recording on evaporated Co/Pt multilayer films