Microstructures and magnetic anisotropy of single-layered Fe-Pt alloy films by in-situ annealing

The single-layered Fe-Pt films with thickness of 30 nm are in-situ deposited directly on Si substrate at various substrate temperatures (Ts) of 350 to 590 degrees C. As the Fe-Pt film is sputtered at substrate temperature is 350 degrees C, it shows (111) preferred orientation and tends to in-plane magnetic anisotropy. The L1(0) Fe-Pt film with (001) texture is obtained and exhibited perpendicular magnetic anisotropy as the substrate temperature is increased to 470 degrees C. The perpendicular coercivity (Hc perpendicular), saturation magnetization (Ms) and perpendicular squareness (S perpendicular) of this film are 6.9 kOe, 674 emu/cm3 and 0.89, respectively, which reveal its significant potential as perpendicular magnetic recording media.     

The promise of new particulate media for high density recording

The superiority of perpendicular recording derives from the very low demagnetization at high bit densities, and from the nearly perfect writing process when a single pole head is used in combination with a double layer medium. Recent experiments have shown that it is possible to record very high densities in the longitudinal recording mode by scaling down all the critical parameters to extremely small values. However, such extreme scaling will very likely be accompanied by some very difficult problems from the point of view of media imperfections, defects, yields and costs. The power of perpendicular recording derives in part from the ability to attain these very high bit densities without resort to extreme scaling of the critical system parameters. There is little doubt that in the long run perpendicular recording will predominate because of its superior performance derived from the advantages stated above. For the next several years, however, we have to look to new and improved particulate media (to satisfy the majority of the demands) which can be fabricated by using existing large capacity continuous web coating facilities. The best choice for satisfying the requirements of these tape-related large volume applications is to utilize the new particulate media which support a large degree of perpendicular magnetization (isotropic-high squareness, and perpendicular anisotropy particulate dispersions) rather than employing very high coercivity longitudianally optimized particulate media.     

Thermal stability improvement for longitudinal magnetic recording media

This paper reports and discusses the effects of M/sub r/t cancellation and bottom/top magnetic layer thickness ratio on thermal stability and recording characteristics of low-noise synthetic antiferromagnetic (SAF) longitudinal recording media. It is shown that by proper design and process, SAF media with low M/sub r/t cancellation can deliver excellent overall recording performance with acceptable thermal stability. We present a unique approach to significantly improve the thermal stability of SAF media with low M/sub r/t cancellation by adjusting the bottom/top magnetic layer thickness ratio. Increasing the bottom/top magnetic layer thickness ratio significantly improves amplitude decay rate and media coercivity temperature dependence with little sacrifice in recording performance.     

Thickness dependence of microstructures and magnetic properties for CoPt/Ag nanocomposite thin films

Ag underlayer (30 nm) has improved the degree of ordering and perpendicular magnetic anisotropy of CoPt films (7.5-10 nm). After annealing at 600 °C and 700 °C, the perpendicular coercivity of CoPt/Ag films has been raised as the thicknesses of CoPt layers are increased. The magnetic easy axis of CoPt/Ag films would change from a random orientation to an out-of-plane orientation. It is found that Ag underlayer with thickness of 30 nm can improve the perpendicular magnetic properties of CoPt layers with thicknesses in the range of 7.5-10 nm. The CoPt/Ag films would be a candidate for perpendicular magnetic recording media.     

The effect of thickness on the texture and magnetic properties of single-layered FePt films by rapid thermal annealing

The single-layered FePt films with thickness in the range of 5 to 50 nm are deposited directly on Si(100) substrate without underlayer, then post annealed at 700 degrees C by rapid thermal annealing (RTA) technique. As the film thickness of FePt is over 20 nm, the L1(0) FePt(111) preferred orientation is presented and tended to in-plane magnetic anisotropy. However, the L1(0) FePt(001) texture is obtained and exhibited perpendicular magnetic anisotropy as the film thickness is decreased to 10 nm. Its perpendicular coercivity (Hc(perpendicular)), saturation magnetization (Ms) and perpendicular squareness (S(perpendicular)) are 14.8 kOe, 795 emu/cm3 and 0.79, respectively. On the other hand, both the grain size and domain size of FePt film decrease with decreasing the film thickness of FePt. The grain size for 10-nm FePt film is as small as 9.7 nm with domain size of 123 nm, which reveal its significant potential as perpendicular magnetic recording media for ultra high-density recording.     

Plasma effects on the Co-Cr deposition in opposing targets sputtering method

It is well known that Co-Cr films show a high perpendicular magnetic anisotropy, coercivity of 1000 oe or above and other properties suitable for perpendicular magnetic recording media. In this report, Co-Cr films, deposited by the bombardment of ions extracted from plasma using a new type of cathode sputtering apparatus with opposing targets, which will be called opposing targets sputtering hereafter, were investigated on morphology, crystal structure and magnetic properties. It was found that in the Co-Cr films of suitable magnetic properties for recording media, the morphology changes and the degree of C-axis orientation of Co-Cr hcp crystal, Δθ50is a constant value as low as about 3° with the increase of ion bombardment energy during deposition. Both morphology and the dependency of Δθ50on thickness of the Co-Cr films deposited by the opposing targets sputtering considerably differ from those by RF sputtering. There was no columnar structure observed in the cross section of the Co-Cr films suitable for perpendicular magnetic recording media prepared by the opposing targets sputtering, whereas columnar structure is reported to be observed clearly in the case of both RF sputtering and vacuum vapor deposition.     

Ag底层对TbFeCo薄膜磁性能的影响

采用射频磁控溅射法在玻璃基片上制备了TbFeCo/Ag非晶垂直磁化膜，研究了Ag底层厚度对TbFeCo薄膜磁性能的影响。原子力显微镜、振动样品磁强计与磁光盘测试仪测量结果表明：薄的银底层具有较高的表面粗糙度可以显著增大TbFeCo薄膜的矫顽力，改善TbFeCo薄膜的磁光温度特性，该薄膜有望用作高密度垂直记录介质与光磁混合记录介质。     

Magnetic properties and microstructures of single-layered Fe100 − xPtx films deposited onto heated substrates

The single-layered Fe_100 − xPt_x films of 30 nm thick with Pt contents (x) of 35-57 at.% are deposited on heated Si (100) substrate at a temperature (Ts) of 620 °C by magnetron co-sputtering. When the Pt content in the Fe-Pt alloy film is 35 at.%, the value of in-plane coercivity (Hc_//) is close to perpendicular coercivity (Hc_⊥) and both values are about 800 kA/m. The FePt films exhibit perpendicular magnetic anisotropy when the Pt content increases to the values of between 45 and 51 at.%. The perpendicular coercivity, saturation magnetization (Ms) and perpendicular squareness (S_⊥) for Fe₅₄Pt₄₆ film are as high as 1113 kA/m, 0.594 Wb/m² and 0.96, respectively. These magnetic properties reveal its significant potential as perpendicular magnetic recording media. Upon further increasing the Pt content to 57 at.%, the coercivity of the Fe-Pt film decreases drastically to below 230 kA/m and tends to be closer to in-plane magnetic anisotropy.     

Review of head-media coupling in magnetic recording

Recent advance of magnetic recording technology has resulted in tremendous increase in area densities. Several new components were developed: Thin film media, and thin film head in longitudinal recording; Single-layer media, double-layer media, and probe head in perpendicular recording. A variety of head and media combinations become possible, and each has a different degree of head-media coupling. The soft magnetic underlayer in double-layer perpendicular media has such a strong coupling with the head that the head and media must be treated as a single entity in the analysis. The evaluation of only a head or a medium without knowing its counterpart could be quite misleading. Optimization of head-media coupling to select the most suitable combination becomes a key factor in designing a high density recording system. We will review the recording and reproducing processes from both the theoretical and experimental aspects for all the head-media structures which have some practical interest.     

Possibilities of perpendicular magnetic recording

The potential of perpendicular magnetic recording using a single-pole head and a double-layered medium has been investigated theoretically by computer analysis and compared with that of longitudinal magnetic recording. In conventional longitudinal recording, a recording demagnetizing loss due to the change of magnetization mode from semicircular to circular shapes occurs with increasing recording level at high bit density. In perpendicular magnetic recording, the perpendicular magnetization mode is maintained regardless of recording level even at an extremely high bit density of 571 kFRPI. This indicates that the perpendicular recording medium has a very high recording resolution, where a single bit size approaches several diameters of the microcrystalline particles of the Co-Cr layer. An ultrahigh density at which the recording area for 1 bit will reach 1 μ² at present and 500 Å₂ in future should be possible     

Ultrafast heating effect on transient magnetic properties of L10-FePt thin films with perpendicular anisotropy

Laser-induced ultrafast magnetization dynamics and transient coercivity behavior in perpendicular magnetized L1₀-FePt films are investigated using the time-resolved polar magneto-optical Kerr technique. The magnetization after photo-excitation shows a dramatic reduction on the picosecond time scale. In contrast, the coercivity shows a weak decrease, accompanied by a skewed Kerr loop shape for low and intermediate fluences. The results can be interpreted by the laser-induced non-uniform demagnetization due to the weakened coupling between FePt grains of different size and/or components. The remaining coercivity vanishes when the film is fully demagnetized at higher fluence. We claim that the remaining coercivity can be manipulated by employing appropriate laser energy and film thickness, which may be helpful for application in heat-assisted magnetic recording.     

Ion-implantation studies on perpendicular media

Magnetic and structural properties of ion implanted perpendicular recording media have been investigated. Effects of 12C+ ion implantation with the doses of 2 x 10(11), 10(13), 10(14) and 10(16) ions/cm2 in the magnetic recording layer of conventional granular and continuous perpendicular media are reported in this paper. Implantation with the highest fluence of 10(16) ions/cm2 resulted in change of the magnetization reversal mechanism, thereby reducing coercivity. In continuous media the implanted ions cause increase in pinning defects, leading to an increase in coercivity. In contrast, high dose was found to cause similar change in the crystallographic properties of both the granular and continuous media.     

FePtAg-C纳米颗粒薄膜的制备及表征

采用磁控溅射法在硅基片上生长FePt纳米颗粒薄膜。在硅片表面生长MgO籽层用来引发FePt合金薄膜的fct织构,加入C来减小其颗粒尺寸,加入Ag来增强其L10有序度。采用X射线衍射仪（XRD）、超导量子干涉仪（SQUID）和高分辨率透射电镜（TEM）对FePt薄膜进行表征。结果表明制备的薄膜样品具有优良的L10相结构,其M-H曲线表明方形度很好,垂直矫顽力HC有2467 kA/m,颗粒大小为10.4 nm。该薄膜非常适合用做下一代高密度磁存储媒质,可有效提高信息存储密度。     

FePt-Ag nanocomposite thin films with longitudinal magnetic anisotropy

A well-controlled method to fabricate FePt thin films with the (200) texture and longitudinal magnetic anisotropy for high-density magnetic recording media is reported. FePt-Ag nanocomposite thin films with L1(0) ordered FePt grains embedded in an Ag matrix were deposited on the Cr90Ru10/glass by co-sputtering from Ag and FePt targets. The Ag doping suppressed the (001) texture but improved the L1(0) FePt (200) texture. The magnetic easy axis of FePt-Ag thin films changed from perpendicular to longitudinal in direction. In-plane coercivity of the films varied from 0.8 kOe to 6.5 kOe, depending on Ag contents in the films and under-layer thickness. The change from the (001) to (200) texture could be due to the competition of grain-boundary energy and epitaxial-strain energy.     

Influence of antiferromagnetic FeMn on magnetic properties of perpendicular magnetic thin films

We studied the influence of an anitferromagnetic FeMn layer on perpendicular magnetic anisotropy (PMA) and perpendicular coercivity (H_C⊥) of the CoCr/Pt multilayers and found that both PMA and H_C⊥ can be enhanced by the FeMn layer. We observed an obvious exchange coupling between FeMn and CoCr/Pt multilayers which enhances PMA and may increase the density of pinning sites that can pin the domain wall of ferromagnetic layers and lifts up energy barrier during the propagation of domain walls. This leads to the enhancement of H_C⊥. Moreover, X-ray diffraction results shows that the (111) texture of the FeMn layer enhances that of the CoCr/Pt multilayers, leading to the increase of PMA and H_C⊥ as well. This result is of great significance on improving magnetic properties of perpendicular magnetic recording media by using an antiferromagnetic manganese alloy.     

Role of bottom layer of double recording layer structure for antiferromagnetically coupled longitudinal media

Double recording layers stacked on a Ru spacing layer are commonly used to obtain good recording properties for antiferromagnetically coupled (AFC) longitudinal media. In this paper, we report on a study that clarified the role of the bottom recording layer (BRL). We measured physical magnetic properties such as magnetic anisotropy field (H/sub k/), magnetocrystalline anisotropy energy (K/sub u/), intergranular interaction, and thermal agitation of the AFC media, with and without BRL. Results showed that: 1) even a thin BRL (1 nm thick) significantly increases remanent coercivity H/sub cr/; 2) this increase in H/sub cr/ is mainly caused by an increase in H/sub k/ due to elimination of the low K/sub u/ region at the bottom portion of the top recording layer; and 3) judging from magnetic cluster size, insertion of a BRL can reduce the intergranular exchange coupling at the initial growth region of the recording layer.     

Eddy currents in conducting magnetic recording media

Use of metallic magnetic recording media raises the possibility that medium eddy currents will influence the recording process. The mathematical analog to diffusion of heat allows exact solutions for cases approximating those of interest. Eddy current effects are shown to be negligible for usual thicknesses of longitudinal and perpendicular media.     

Influence of initial growth layer and Ti underlayer on magneticproperties and recording characteristics of very thin films ofevaporated Co-Cr media

A Co-Cr film deposited directly on a substrate has an initial growth layer with low coercivity. However, the existence of a Ti underlayer prevents the formation of such a layer. As a result, Co-Cr film deposited on a Ti underlayer has high perpendicular anisotropy and coercivity even in cases of extremely thin film thickness (200 Å). As for the read-write characteristics of Co-Cr thin-film media, the existence of such an initial growth layer greatly improves the reproduced output level. The cause for this is considered to be that the free charges which appear on the back surface of the perpendicular recording layer are reduced and the demagnetization field acting on the recorded magnetization subsequently decreases due to the existence of the initial growth layer     

High coercivity in nanostructured Co-ferrite thin films

Three methods including sol-gel, rf sputtering and pulsed laser deposition (PLD) have been used for the fabrication of high coercivity Co-ferrite thin films with a nanocrystalline structure. The PLD method is demonstrated to be a possible tool to achieve Co-ferrite films with high coercivity and small grain size at low deposition temperature. High coercivity, over 10 kOe, has been successfully achieved in Co-ferrite films with a thickness of ∼ 100 nm deposited using PLD with a substrate temperature at 550°C. The Co-ferrite films prepared by PLD at over 300°C on different substrates including amorphous glass, quartz and silicon exhibits an obvious (111) textured structure and possesses perpendicular anisotropy. Our study has also shown that the high coercivity is related with a large residual strain, which may induce an additional magnetic anisotropy (stress anisotropy) and at the same time serve as pinning centres, which can restrict the domain wall movement and therefore, increase the coercivity.     

Effect of Ag underlayer on microstructures and perpendicular magnetic properties of CoPt nanocomposite thin films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of degree of ordering and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a large degree of ordering and a perpendicular magnetic anisotropy after annealing at 700 degrees C for 30 min. CoPt/Ag films with out-of-plane coercivity (Hc (perpendicular)) in the range of 13.5-14.0 kOe and a out-of-plane squareness (S(perpendicular)) of 0.97 were obtained after annealing at 700 degrees C for 30 min. Ag underlayer is beneficial to enhance the Hc(perpendicular)and S(perpendicular) of CoPt film significantly. The degree of ordering and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.