TbFeCo Films Research Articles

Preparation and magnetic properties of TbFeCo on the porous alumina templates

A self-ordered hexagonal array of nanopores has been fabricated by anodizing a thin film of Al on glass and subsequently the magnetic properties of TbFeCo on this templates were studied. We carried out anodic oxidation of a sputtered Al film at the anodic voltage in the range of 10–30 V and temperature in the range of 5–40 °C, and found that the density of the nanohole arrays increased with the decrease in anodization voltage and temperature. On the other hand, hole diameter decreased with the decrease in anodic voltage and temperature. Then TbFeCo was deposited onto this porous array by sputtering with a thickness of around 90 nm and subsequently was overcoated with 10 nm SiN for the protection from surface oxidation. The TbFeCo deposited on this porous layer shows complete perpendicular anisotropy and the AAO template can promote the growth of the microcolumnar structure in TbFeCo films. The coercivity increased with the decrease of hole diameter. The coercivity of the TbFeCo deposited on the porous array with a mean hole diameter of around 15 nm is 5.6 kOe and larger than that on bare glass, but the squareness ratio gets poorer than that on bare glass. It seems that there were no significant changes in Ms and Kerr rotation angle.

Toward 10TB Cartridge Capacity with Magneto-Optical Recording on Ultra Thin Discs

Magneto-Optical (MO) recording on ultra thin discs with 92 μm thickness succeeded. Key technologies are a nano-imprint for embossing on the thin disc and aerodynamic stabilizer (ADS) for stable disc rotation. The ADS made the thin disc rotation stable by providing an air cushion between the glass stabilizer and thin disc. The ADS was also available for the thin disc with a magnetic flying head. Using TbFeCo film, the thin disc had almost the same performance as that of a normal disc with 1.2 mm thickness. Stacked Volumetric Optical Discs (SVOD) can enhance the volumetric capacity with a lot of thin discs stored in a compact cartridge. Because the 40 nm mark length recording corresponds to the 100 GB/disc with CD size which has already succeeded in MO recording, the combination of MO recording and SVOD with 100 thin discs will enable the possibility to provide a 10 TB cartridge capacity.

Sputtering gases and pressure effects on the microstructure, magnetic properties and recording performance of TbFeCo films

The MsHc value is considered to be a key factor in high-density recording, and controlling the microstructure on the magnetic underlayer was found to be an effective way of increasing the MsHc of the amorphous TbFeCo magneto-optical (MO) medium. In this paper, we investigate the TbFeCo film's magnetic properties and the effects on the microcolumnar structure, which depends on the sputtering conditions of using various sputtering gases including Ar, Kr, and Xe, and the recording characteristics of TbFeCo memory layers. With heavy sputtering gases such as Kr or Xe, the columnar structure can be prepared in a TbFeCo film at a pressure lower than 1.0 Pa. The columnar structure of a recording layer can be effectively formed thanks to the effects of the magnetic underlayer, which has a fine surface even in the sputtering process in which Xe gas is used. The above applies to the sputtering process in which Ar gas is used. Also, when Xe gas is used in the sputtering process, coercivity Hc is increased through the formation of a well-segregated microcolumnar structure built on domain wall pinning sites, and we obtain a large MsHc and a high squareness ratio of the Kerr-hysteresis loop. Our results indicate that processing a TbFeCo film with heavy sputtering gases is suitable for tiny mark stability because the temperature gradient of Hc is increased. The objective of the low-pressure sputtering process using Xe gas to produce the columnar structure is to achieve ultra-high-density recording with tiny mark stability in the TbFeCo medium. This has been confirmed with magnetic force microscope (MFM) images of stable tiny marks recorded on TbFeCo film.

Perpendicular magnetic anisotropy in TbFeCo films studied by magnetic Compton scattering

Magnetic Compton profiles (MCPs) of TbFeCo amorphous films have been measured from a viewpoint of perpendicular magnetic anisotropy (PMA). Analysis of anisotropies of the MCPs has shown that anisotropies of wave functions are small in both a PMA film and an isotropic magnetization (IM) film. Element selective analysis of the MCPs has shown that a Tb magnetic moment and a magnetic moment of 3d transition metal (TM) are coupled antiparallel in the PMA film. In the case the IM film, the magnetic moment of 3d TM tends to align toward the magnetic field but the Tb magnetic moment distributed to random orientations. The PMA natures reflect the magnetic structures of the Tb magnetic moment and the 3d TM magnetic moment in the TbFeCo films.

Properties of microstructure on amorphous film of rare earth–transition metal alloy for ultrahigh density recording

Controlling the microstructure of amorphous rare earth–transition metal films via the sputtering process was found to be an effective way of controlling their magnetic properties for applications as magneto-optical storage media. This paper describes how the relationship between a TbFeCo film’s magnetic properties and its microcolumnar structure depends on the sputtering conditions. An enhancement of electric resistance value was observed for the devices with a constriction columnar width in the 5–20nm range. The measured electrical resistance was over 1.0×10−5Ωm in this case. It is believed that the change of electrical resistance on the thin film is due to fluctuations in the density on the arranged microstructure or constriction of current induced by scattering because the film structure contains impurities. These same impurities are believed to be associated with the restriction of the trapped domain wall’s mobility. Furthermore, we observed a significant resistance change subsequent to the application of lower Xe pressure sputtering. This paper also serves as a feasibility study for high-density magneto-optical recording on these media materials.

Magnetic properties of TbFeCo film with Ag under-layer

Tb 19.05Fe 22.01Co 58.94 (500 Å)/Ag (0–1000 Å) double films were deposited on nature oxidized Si(1 0 0) substrates at room temperature by DC magnetron sputtering. The TbFeCo /Ag films were sandwiched between two 300 Å SiN x protective layers which were prepared by RF magnetron sputtering to prevent the films from oxidation. The effects of Ag under-layer on the magnetic properties of the TbFeCo film were investigated. It was found that increasing the thickness of Ag under-layer would rise the perpendicular coercivity of the TbFeCo film. The perpendicular coercivity value of the TbFeCo (500 Å)/Ag (500 Å) films was 3176 Oe. This film is a promising candidate for heat-assisted magnetic recording media applications.

Perpendicular magnetic anisotropy in sputtered amorphous TbFeCo films

Local chemical bonding and magnetic Compton profiles were used to study the origination of perpendicular magnetic anisotropy (PMA) in amorphous TbFeCo films. Experimental results suggested oxygen atoms can change the local chemical bonding. Anisotropic chemical bonding of Fe3d and Tb4f electrons are found for films with suitable oxygen composition. It is concluded that the origination of PMA in amorphous TbFeCo films is related to the composition of oxygen atoms in the films.

Near-field optically assisted hybrid head for self-aligned plasmon spot with magnetic field

Magneto-optical hybrid head is one of the key devices for the optically assisted magnetic recording. However, there has not been enough research about the hybrid head. Here, we present a near-field optical advanced hybrid (NOAH) head, which makes a self-aligned plasmon spot with a magnetic field. Since a near-field optical intensity distribution is strongly affected by the presence of the recording medium, the shape of the electrode is analyzed by a finite difference time domain method with the TbFeCo film as the recording medium. We calculate the dependences both for the optical and magnetic characteristics on a gap distance between the electrode and the recording medium. The NOAH head makes the sharp distribution of light intensity (full width at half maximum ∼40nm) with the magnetic field ∼29Oe∕mA in the case for 5nm in gap distance. We also calculate the dependence of the plasmon effect on electrode materials. It is revealed that the material which has a high extinction coefficient shows a high peak intensity. A fundamental experiment for the writing on a Cu phthalocyanine dye film is also reported for testing the method to use a glass slider.

Influence of spin polarization enhancement layer to rare earth–transition metal thin films for perpendicular tunneling magnetoresistance evaluated by ferromagnetic Hall effect

Magnetic properties of ion beam sputter-deposited TbFeCo and GdFeCo thin films with their compensation point were studied using ferromagnetic Hall effect measurement. Gdx(Fe90Co10)1−x thin films sputter deposited using Kr exhibited high squareness ratio and sharp magnetization reversal compared with those prepared using Ar as sputtering gas. Lower kinetic energy of sputtering ions was effective to attain higher squareness ratio. Ferromagnetic Hall effect clarifies the magnetization reversal process of a FeCo(xnm) layer contacted to a TbFeCo(50nm) layer. FeCo layer with thickness less than 2nm is magnetized together with TbFeCo layer. Ferromagnetic Hall measurement is a powerful tool to determine the magnetization process of very thin films and magnetically coupled layers.

Phase segregation and exchange biasing in TbFeCo films with perpendicular anisotropy

A TbFeCo film was deposited by DC magnetron sputtering and studied by transmission electron microscopy, polar and longitudinal magneto-optical Kerr effect, and magnetometry measurements. Transmission electron microscopy has shown the existence of lateral compositional inhomogeneity. Magneto-optical measurements have shown that the initial layer at the bottom consists of only magnetic perpendicular component and the top surface layer has a compositional inhomogeneity and consists of in-plane components and perpendicular one. The perpendicular components in the bottom and the surface layers have identical composition. Two in-plane components have been shown by magnetometry measurements. It is shown that phase segregation exists in the TbFeCo film and possible form of compositional inhomogeneity has been discussed. The two in-plane components are exchange coupled with a magnetization off-alignment of 35°. For the soft in-plane component, the in-plane and out-of-plane angular dependence of the exchange biasing is similar to those of the conventional one. Within temperatures from 100 to 300 K, the exchange field and the coercivity are both linear functions of temperature.

Phase segregation and exchange biasing in TbFeCo films with perpendicular anisotropy

A TbFeCo film was deposited by DC magnetron sputtering and studied by transmission electron microscopy, polar and longitudinal magneto-optical Kerr effect, and magnetometry measurements. Transmission electron microscopy has shown the existence of lateral compositional inhomogeneity. Magneto-optical measurements have shown that the initial layer at the bottom consists of only magnetic perpendicular component and the top surface layer has a compositional inhomogeneity and consists of in-plane components and perpendicular one. The perpendicular components in the bottom and the surface layers have identical composition. Two in-plane components have been shown by magnetometry measurements. It is shown that phase segregation exists in the TbFeCo film and possible form of compositional inhomogeneity has been discussed. The two in-plane components are exchange coupled with a magnetization off-alignment of 35°. For the soft in-plane component, the in-plane and out-of-plane angular dependence of the exchange biasing is similar to those of the conventional one. Within temperatures from 100 to 300 K, the exchange field and the coercivity are both linear functions of temperature.

TiN underlayer and overlayer for TbFeCo perpendicular magnetic recording media

TiN thin film is prepared by DC reactive sputtering in Ar+N 2 atmosphere and its suitability as underlayer and overlayer for TbFeCo perpendicular recording media as well as its effect on the magnetic properties of the latter have been studied. Only 5 nm TiN overlayer and 20 nm under layer can successfully protect the TbFeCo film from oxidation. Initially the coercivity is increased sharply from about 2 to 6 kOe for an increase of underlayer thickness to 60 nm then the increasing rate of coercivity becomes very slow. The saturation magnetization remains almost constant with the underlayer thickness. The remanent squareness ratio remains constant at 1.0 with the underlayer thickness up to 60 nm then decreases.

LLG Simulations of TbFeCo/FeNiPt CGC-Like Film

Recently, much attention has been focused on so-called “hybrid recording” such as “optically assisted magnetic recording” or “heat assisted magnetic recording”. In other words, hybrid recording is expected to be a most promising storage device beyond 1 Tera bit/inch2, ultra high density region. When the domain radius becomes very small in magneto optical recording film, the wall energy is dominant in the total energy of the domain, and then it will shrink and disappear. To write a very small domain, it is necessary to increase the domain wall coercivity to freeze the written domain. We perform three-dimensional Landau-Lifshitz-Gilbert (LLG) simulations for estimating domain shapes and wall structures in coupled granular and continuous (CGC) like films of TbFeCo film/FeNiPt grains. In the results, even when using lower Tc FeNiPt (Tc= 307 °C, Ku= 1.8×107 [erg/cm3] at room temperature) grains than FePt (Tc = 497 °C, Ku = 7.0×107 [erg/cm3] at room temperature) grains, we find a minute magnetic domain of 26 nm diameter, could be made on TbFeCo /FeNiPt bi-layer film. Moreover, the domain wall width, the obstacle in the minute magnetic domain structure of bi-layer film, is narrow. This narrowness advantageously contributes to a high density recording.

Magnetoresistance in amorphous TbFeCo films with perpendicular magnetic anisotropy

The magnetoresistance of TbFeCo amorphous films with perpendicular magnetic anisotropy have been studied at room temperature. TbFeCo films within a thickness range of 50–300nm were deposited by a dc-magnetron sputtering. Sharp change in magnetoresistance (MR) has been found at the magnetization reversal region. The MR ratio is sensitively dependent on the film thickness and the magnetic domain pattern. Films with smaller domain pattern show higher MR ratio. The MR ratio is decreased with the decrease in film thickness. It may be considered that the observed MR is contributed from the domain wall. The maximum MR ratio is about 3.7% for the film with thickness of 300nm at room temperature. No MR has been found when the magnetic field is applied parallel to the film plane.

Analysis on a new type magneto-optical disk for blue lasers

The conventional TbFeCo magneto-optical (MO) medium has a relatively smaller Kerr rotation angle in the blue region than in the red. With the recording wavelength gradually moving to the short wavelength, if TbFeCo is still used as recording medium, the conventional MO disk structure must be optimized to get a larger carrier to noise ratio (CNR). Sabi et al. have found that adding a metal layer attached to the TbFeCo film as thermal control layer is a useful way to get a high CNR. In this paper, we proved this through calculation, and carried out optimization of the new type of disk. Calculation results showed that the new structure is useful in preventing an excessive temperature increase, and has a better thermal response.

Effect of Underlayer Surface Morphology on the Magnetic Properties of TbFeCo Film

We studied the magnetic properties of TbFeCo thin film sputtered onto TiN underlayer with different surface morphologies resulted from different thicknesses. According to the results of atomic force microscopy, the surface roughness of TiN film is increased as the film thickness increased. Initially the coercivity is increased sharply from about 2 kOe to 6 kOe for an increase of underlayer thickness to 60 nm then the increasing rate of coercivity becomes very slow. At about threefold increase in the coercivity is thought to be due to the enhancement of domain wall pinning effects caused by an increase of surface roughness in the TiN underlayer. For the underlayer thickness of more than 60 nm, the M-H loop has been changed from rectangular to nonrectangular resulting remanent squareness ratio of less than unity. There is no significant effect of TiN underlayer thickness on the saturation magnetization has been observed.

TbFeco film with W underlayer and overlayer for perpendicular magnetic recording

TbFeCo film is prepared with W underlayer and overlayer to protect the film from oxidation and its effect on the magnetic properties and domain structure of the film has been investigated. Only 5nm overlayer and 20nm underlayer can successfully protect the film from oxidation. The saturation magnetization increases with increase in underlayer thickness and the effect is more pronounced when TbFeCo films become thinner. W underlayer is very effective to prevent the reduction of remanent squareness ratio (S) with decrease in magnetic layer thickness. The value of S is 1.0 and 0.8, for the films with and without underlayer, respectively, where magnetic layer thickness was 15nm. In magnetic force microscope observations, average magnetic domain size is reduced when W underlayer and overlayer are used.

Magnetic Characteristics of TbFeCo Fabricated on Isolated FePt Grains

TbFeCo film is fabricated on isolated FePt grains to increase the domain wall coercivity (Hw) of TbFeCo film by exchange coupling effect between TbFeCo and FePt. The transition metal (TM) moment has a dominant charge in TbFeCo film ranging from room temperature (Troom) to Curie temperature. The FePt has average grain sizes such as 29.6, 16.6 and 7.0 nm in diameter, which are perpendicularly magnetized with a high coercivty (Hc), as high as 30-45 kOe at Troom. The TbFeCo/FePt composite film shows higher Hw, Hc, and MsHw than those of the single layer of TbFeCo film. We also estimate the amountof interfacial wall energy between TbFeCo and FePt.

Ultrahigh-density magneto-optical recording based on the effect of plasmon excitations

The analysis of ultrahigh-density recording in magneto-optical media formed with the use of granular CoAg(Au) films is performed. Due to excitation of plasma oscillations of electrons in granular CoAg(Au) films, the latter make it possible to perform additional focusing of recording radiation and to significantly decrease the size of memory cells. It is suggested that two-layer film CoAg(Au)/TbFeCo/substrate systems be used as recording media for magneto-optical recording. It is shown theoretically that the angle of the Kerr rotation of the plane of polarization θK upon magnetization of such a two-layer structure increases significantly in the range of incident-photon energy from 2 to 4 eV in comparison with the case of TbFeCo magnetic film. Some specific features were detected experimentally in the spectra of θK in the region of excitation of plasma oscillations in nanogranular CoAu and CoAg films at ℏ ω P ≈ 2.5 and 3.5 eV, respectively, as well as in two-layer CoAg(Au)/TbFeCo film systems.

A computational method of temperature characteristics of magneto-optical Kerr effect in amorphous TbFeCo films with a multilayered structure

A computational method for evaluating temperature characteristics of the Kerr rotation angle, Kerr ellipticity, and thus the readout signal-to-noise ratio of an amorphous TbFeCo film with a multilayered structure is presented. In this method, a generalized mean-field theory for an n-component system is applied to analyze the temperature dependence of the sublattice magnetizations and the total saturation magnetization of the ternary TbFeCo alloy, and the characteristic matrix method of film optics is adopted to analyze the magneto-optical Kerr effect in the multilayered film. By using this method, the optimum power of the readout laser for a practical magneto-optical disk structure can be determined. As an example, we present a calculation on the Tb0.21Fe0.66Co0.13 quadrilayer disk structure. The result shows that the Kerr rotation angle, Kerr ellipticity, and the readout figure of merit of the quadrilayer structure decrease monotonically with increasing temperature, similar to the variation of Fe sublattice magnetization with the temperature, MFe(T). The calculated temperature dependences of the saturation magnetization MS(T) and the Kerr rotation angle θK(T) are in good accordance with the previous experimental results.