Film Magnetic Recording Media Research Articles

Segregation effects of doped VN and ZrN on magnetic and microstructural characteristics of FePt-based films

Segregants are essential materials for forming the complexation or granular microstructure in thin films for magnetic recording media. One such film, FePt-BN, has a metallic L10 FePt main phase as its matrix, in addition to having BN and C segregants at the grain boundaries. Amorphous BN has sufficient mechanical strength to support the columnar growth of FePt grains, however, it has a lower deposition rate resulting in columnar grains with a nonuniform aspect ratio. Moreover, some B diffuses in the interstitial site of FePt lattices. To overcome these limitations, this study added the transition nitride VN and ZrN with equal volume percentages to replace some BN segregants in FePt(BN, Ag, C) films: substantially different segregation behaviors were observed. Microstructural imaging mapping revealed that although VN segregated the FePt grains boundary, ZrN was diffused in the lattice. The FePt-BN-ZrN film thus had more disordered grains contributing to a higher in-plane magnetization and wider hard axis magnetic hysteresis loops than did FePt-BN-VN. The FePt-BN-VN film has the highest perpendicular magnetic anisotropy constant (Ku= 2.17 × 106 J/m3) and coercivity (Hc= 4 T); moreover, parallel remanence magnetization was minimal with a linear in-plane magnetization loop. The FePt-BN-VN film was sputtered directly on MgO(100) but depositing the FePt-BN-ZrN film required a 2-nm-thick FePt nucleation layer. The high atomic number of Zr and high sputter yield ratio (YN/Ymetal) of ZrN may increase the sites occupied by N, potentially affecting ZrN segregation.

Effect of carbon mixing on the degree of perpendicular texture of FePt:C nanocomposite film for magnetic recording media

The effect of carbon mixing on the perpendicular magnetization of magnetron sputtered FePt thin films was studied using magnetic property measurement and X-ray diffraction, and TEM microscopy. Micromagnetic simulation was carried out to study the effect of texture on the perpendicular coercivity. Unlike general conviction, the mixing of FePt with carbon led to a significant enhancement in the perpendicular magnetization. The maximum enhancement of perpendicular magnetization was observed at about 20 vol.% of carbon, where carbon amorphous film started to completely enclose the individual FePt grains. This reason was explained that the epitaxial growth and thus perpendicular texture of ordered FePt grains were maximized due to the relaxation of coherency for epitaxial growth which was maximized in the isolated grains. The perpendicular coercivity reached 8500 Oe, while the in-plane coercivity (120 Oe) remained negligible. The simulation showed that the enhancement of perpendicular texture can largely increase the perpendicular coercivity of FePt:C thin film.

Fabrication of FePt Films for Magnetic Recording Media

The FePt films were fabricated by using RF sputtering for magnetic recording media. The efforts have been done to reduce the grain size, to decrease the ordering temperature, and to control the crystalline orientation. It was found that the proper amount of alumina led to decrease the grain size and weak the interparticle exchange coupling. 15% N 2 partial pressure can reduce the transform temperature from fcc to fct phase. In order to control the texture in the FePt films, two kinds of methods were used. On the one hand, the addition of W in Cr underlayer and the usage of Mo and Pt as intermediate layer caused the texture of FePt films changed from (200) to (001). On the other hand, the (Pt/Fe) n multilayers were fabricated to produce the FePt (001) orientation.

Study of the grain growth mechanism of CoPt/Cn thin film for magnetic recording media using the Monte Carlo simulation

The effect of carbon addition on the grain growth and ordering kinetics of CoPt film has been studied experimentally by sputter-depositing a monolithic CoPt-20 at.%C film of 24nm. The carbon addition of 20 at.% to CoPt thin film in the form of CoPt (20nm)/Cn (4 nm) (n=1, 4) significantly reduced both the grain growth and ordering kinetics. Reducing the thickness of the carbon layer, i.e. from n=1 to n=4, led to a much finer grain size distribution as well as to a finer grain size. The Monte Carlo simulation study indicated that the decrease of grain growth and ordering kinetics is primarily due to a continuous decrease of the mobility of the order—disorder inter-phase with the progress of the ordering reaction. Reduction of the inter-phase mobility can eventually lead to a stable two phase grain structure inter-locked by low mobility inter-phase and is responsible for the formation of a fine grain size distribution in the CoPt/Cn film with n=4.

Developing SmCo5 perpendicular magnetization thin films for magnetic recording media

A series of our studies on sputter-deposited SmCo5 thin films exhibiting very high perpendicular magnetic anisotropy is reviewed. Introduction of a Cu underlayer is a key to imparting perpendicular magnetic anisotropy to SmCo5 thin films. Perpendicular magnetic anisotropy was enhanced by depositing the Sm-Co layer with the alternate lamination of Sm and Co sublayers and by using the Cu/Ti dual underlayer for producing a smooth film surface. As a result, under an optimized condition, the magnetic anisotropy constant was as large as 4.0 x 107 erg/cm3, which is greater by a factor of ten than that of material used for conventional magnetic recording media. Furthermore, we found that high perpendicular magnetic anisotropy was obtained even in very thin films and that the coercivity was controllable in a wide range when the films were prepared using an ultra-high vacuum sputtering system. Microstructural analysis suggested that the Cu-rich region in the initial growth stage of the Sm-Co layer played an important role in generating perpendicular magnetic anisotropy. In addition, we tested SmCo5 thin films for use in conventional and heat-assisted magnetic recording media.

Nanostructure of CoPtCr–SiO<SUB>2</SUB> Granular Films for Magnetic Recording Media

Structural properties of CoPtCr–SiO2 magnetic recording films grown on Ru or Pt seed layers prepared by UHV-magnetron sputtering were studied by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM). CoPtCr grown on Ru seed layers together with SiO2 forms a well-isolated structure composed of CoPtCr fine grains of 10 nm diameter surrounded by amorphous SiO2, whereas CoPtCr grown on Pt seed layers together with SiO2 forms a network structure composed of CoPtCr crystal of 5 nm size. These structural features made differences in their magnetic properties. The HRTEM and EFTEM studies revealed that cylindrical crystalline grains composed of CoPtCr and Ru are formed for CoPtCr–SiO2/Ru samples, whereas SiO2 are aggregated around the boundary between relatively large Pt grains and magnetic layers without obstructing the epitaxial growth of CoPtCr on Pt, not resulting in the cylindrical CoPtCr grains. Lattice spacings of CoPtCr grown on Pt with SiO2 are 0.7% expanded in comparison with CoPtCr grown on Pt without SiO2. The EELS studies suggested that Co and Cr atoms are partly oxidized by SiO2 addition for both samples and Cr atoms are more oxidized for CoPtCr–SiO2/Pt samples.

The Field- and Zero-Field-Blocked transverse susceptibilities for high-density recording media

Abstract This paper discusses a new method for measuring the transverse susceptibility of thin film magnetic recording media, which uses a DC probe field. The proposed method allows the measurement of modern hard-disk media, unlike the previously reported methods. Two components of the DC transverse susceptibility are defined, denoted by Zero-Field-Blocked and Field-Blocked, that allow a straight-forward interpretation of the thermal relaxation effects on the transverse susceptibility.

Texture in films: Selected examples

The paper contains a brief discussion of research on texture and properties of films. Three examples are selected to illustrate problems of understanding of texture development and correlation between texture and properties of films. Various correlations between texture related structural characteristics of film and probability of failure of Al-Cu interconnects line are presented to illustrate the need for a better understanding of the correlation between texture and failure mechanism. Another example on development of texture in nickel films illustrates processes that influence texture development and type of interfaces between oxide grains. It is demonstrated that texture and grain boundary character distribution decides the rate of oxidation of Nickel. An example of Co-Cr films for magnetic recording media illustrates an important role of texture in controlling the magnetic properties of films for application in perpendicular magnetic recording. Principles of methods that are used to calculate texture influence on magnetic properties are discussed.

Studies on the effect of Cobalt and Titanium substitution in NdFeB thin films for magnetic recording media

We have investigated as series of substituted NdFeB thin films (NdFeBX where X = Co, Cu, Ti, Zr partially replacing Fe) of different thickness. The perpendicular coercivity has a maximum of 2700 Oe for a thickness of 200 nm after annealing at 625°C for 15 mins. It is found that coercivity can be controlled by varying the thickness of the films. We have observed that the grain size is controlled to less than 25 nm in the substituted films.

Co-O Evaporated Films for Magnetic Recording Media

Co-O Evaporated Films for Magnetic Recording Media

Preparation of Co Ferrite Thin Films for Magnetic Recording Media by the Ferrite-Plating Method

Preparation of Co Ferrite Thin Films for Magnetic Recording Media by the Ferrite-Plating Method

Underlayer and substrate effects in RF-magnetron sputtered barium ferrite thin film media

The effect of employing various sputtered underlayers and commercially available substrates in order to optimize the characteristics of barium ferrite (BaM) thin films for magnetic recording media have been studied. Our results show that the choice of underlayer or substrate controls the resultant surface morphology and magnetic properties of the BaM film. In particular, it was found that barium ferrite thin films with high coercivity, good squareness, low switching field distribution (>5000 Oe, 0.92, and 0.58, respectively) and possessing a c-axis in-plane orientation texture were achieved when deposited on an amorphous sputtered underlayer of Al/sub 2/O/sub 3/. In addition, the use of an Al/sub 2/O/sub 3/ underlayer results in equiaxial barium ferrite grains which may allow a favorable reduction in intergranular interaction as evidenced by the characteristic /spl Delta/M curves.

Surface Potential and Magnetic Recording Media Tribology©

A Kelvin probe apparatus was developed to profile surface potential. Measurements were performed on unlubricated and lubricated carbon overcoated thin film magnetic recording media. The surface potential on perfluoropolyether-lubricated media was more negative than that on the unlubricated carbon overcoat. Sliding, start/slop, and low-flying tests were performed with two-rail sliders, and the surface potential was measured across the test tracks prior to detectable mechanical wear. The surface potential in the lest tracks became more negative with the number of cycles during sliding or start/stop and with decreasing slider-disk spacing during low flying. Degraded lubricants with polar carboxylic acid end groups accumulate and increase the dipole moment in the lest tracks. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Thermal activation and switching in c-axis aligned barium ferrite thin film media

The thermal activation volume and the magnetic switching volume were measured in c-axis uniaxially in-plane oriented barium hexaferrite thin film magnetic recording media. Excellent agreement among the experimental data obtained independently from the magnetic viscosity measurements and the measurements of the time dependence of coercivity implies that the thermally driven process is the cause of both phenomena. The presence of incoherent switching during magnetization reversal is indicated by the in-plane angular dependence of coercivity and is believed to cause the much smaller activation volume and switching volume than the grain size as determined from a TEM micrograph.

Magnetic force microscopy (MFM) studies of micromagnetic structures of high coercivity CoCrPt/Cr and CoCrPtB/Cr thin films

The magnetic microstructures of high coercivity CoCrPt/Cr and CoCrPtB/Cr films were investigated using magnetic force microscopy (MFM). Experiments show that the MFM technique can be used for both qualitative and quantitative description of the magnetic microstructure of high coercivity films for magnetic recording media. It was found that the magnetic microstructure was more refined for films with higher coercivity. The roughness of the magnetic images tend to decrease with increasing coercivity and decreasing media noise. Magnetic images obtained for films with ac-erased state consisted of rounded, symmetric features indicating presence of magnetic vortices. Images from samples in remanent coercivity state showed elongated transitions between regions with different magnetization direction.

The effect of probe-tip geometry on force microscopy images

The atomic force microscope (AFM) has been used to characterize a variety of surfaces to study the influence of the instrumental parameters and sample topography on the interpretation of the images and the data obtained. The effect of the tip shape on the resulting image resolution and artifacts has been studied. Test samples of varied topography have been used to establish imaging parameter optimization for specific sample topographies.Chromium thin films of different thickness, deposited uniformly by rf diode sputtering, have been selected as test samples and imaged with a variety of tip shapes. These films were developed as underlayer films for magnetic recording media used in computer hard disks. The range of tips include commercial silicon nitride pyramidal tips, focused ion beam (FIB) sharpened silicon nitride pyramidal tips, and electron beam contamination induced tips (microtips) varying in growth time (i.e. length) from 10 to 40 seconds (approximately 0.40 to 0.65 μm).

小特集 磁気記録媒体の現状と将来 めっき垂直記録媒体の高記録密度化

小特集 磁気記録媒体の現状と将来 めっき垂直記録媒体の高記録密度化

小特集 磁気記録媒体の現状と将来 スパッタ法による高密度磁気記録媒体

小特集 磁気記録媒体の現状と将来 スパッタ法による高密度磁気記録媒体

小特集 磁気記録媒体の現状と将来 Ｃｏ‐Ｃｒ磁気記録媒体の組成分離構造

小特集 磁気記録媒体の現状と将来 Ｃｏ‐Ｃｒ磁気記録媒体の組成分離構造

Simulations of torque measurements and noise in thin film magnetic recording media

Numerical simulation of micromagnetic processes in thin-film recording media has been utilized to study the relation between high field torque and transition noise. It has been shown that high field torque depends only on the distribution of grain anisotropy axes and not on the local magnetostatic and exchange interactions. In contrast, the medium noise depends critically on local interactions, in particular the intergranular exchange interaction. Thus, for the range of orientations in this study and by inference all orientations, there is no direct relation between noise and high field torque. It is concluded that other phenomena are likely occurring when magnetic thin films are produced with varying out-of-plane anisotropy orientation, and the transition noise appears to be correlated with high field torque measurements. >