TbFeCo Films Research Articles

Measurement of thermal conductivities of SiN and TbFeCo films

The effective thermal conductivities of SiN and TbFeCo thin films were measured by comparing the length and width of a polarizing microscope image of thermo-magnetically written domains with those of calculated isotherms for the trilayer structure of substrate/Si/sub 3/N/sub 4//Tb/sub 22/Fe/sub 70/Co/sub 8//Si/sub 3/N/sub 4/. The resulting data were applied to the quadrilayer structure of substrate/Si/sub 3/N/sub 4//Tb/sub 22/Fe/sub 70/Co/sub 8//Si/sub 3/N/sub 4//Al, and the length of the calculated isotherms turned out to agree with that of the written domain.

Recorded mark observation by spin-polarized scanning electron microscopy

We observed the shape and size of marks recorded magneto-optically on TbFeCo film, using spin-polarized scanning electron microscopy (spin SEM). We studied the laser power dependency of the marks recorded on a land/groove substrate. When larger power was used, the land/groove border acted as a barrier to the propagation of the magnetization reversal, which confirms the advantage of using a land/groove substrate for high-density recording. We also looked at the film roughness dependency of the marks. We found that the magnetization reversal processes depend on the underlayer roughness, which is related to the irregularity of the mark shapes and the recording noise.

COERCIVITY MECHANISM IN DATA STORAGE MEDIA

The coercivity mechanism in polycrystalline CoCrPt thin films, Co/Pt multilayer systems and in amorphous TbFeCo thin films was studied by analyzing the field and time dependencies of the magnetization. The initial susceptibility X0 and the apparent coercivity as deduced from measuring minor loops indicate a much larger contribution of reversible magnetization processes and a much broader switching field distribution in the polycrystalline CoCrPt magnetic recording medium as compared to the perpendicular magneto-optic Co/Pt and TbFeCo media. The magnetic interactions in the media have been determined by δM measurements yielding the strongest interactions in the amorphous TbFeCo films and the smallest in the polycrystalline CoCrPt films. Analyzing the relaxation behavior of the magnetization the Barkhausen volume was estimated for all the three media and compared with the results from microstructure analysis by TEM and AFM.

Magnetic, magneto-optical and dynamic characteristics of exchanged-coupled NdTbFeCo/TbFeCo films for 532 nm recording media

A magnetic, magneto-optical and structural study was performed on exchanged-coupled (EC) layers between NdTbFeCo and TbFeCo films for 532 nm recording media. The saturation magnetization (Ms) of separate read-out (RO) and storage (ST) films varied from 177 to 269 emu/cm/sup 2/ and from 73 to 87 emu/cm/sup 2/, respectively, in the sputtering power range 0.4 to 0.73 kW, at a fixed Ar gas flow rate. Coercivity (Hc) and Kerr angle (/spl theta//sub k/) of RO were in the range 0.46 kOe to 0.65 kOe and 0.34/spl deg/ to 0.38/spl deg/, respectively, for Ar gas flow rate between 15 to 40 sccm, and no great changes were found in the surface morphologies, as observed with atomic force microscopy (AFM). Hc and squareness rose from 2 kOe to 6 kOe and 0.6 to 0.98 with increasing R from 1.5 to 8, where R is the thickness ratio of NdTbFeCo to TbFeCo (total thickness 200 /spl Aring/, 250 /spl Aring/) in the five layered system SiN/sub x//NdTbFeCo/TbFeCo/SiN/sub x//Al-Ti. The carrier-to-noise ratio (CNR) increased by about 8 dB, as R was raised from 1.5 to 3. The films were prepared by magnetron rf-dc continuous sputtering. No atomic mixing between NdTbFeCo and TbFeCo layer occurred, as confirmed by TEM cross sectional observations.

Quantitative determination of the oxygen partial pressure effect on the perpendicular magnetization of TbFeCo thin films

The oxygen partial pressure during the sputter process of TbFeCo thin films was controlled precisely. The effect of the oxygen partial pressure on the perpendicular magnetization of TbFeCo films was quantitatively studied. Between 5.4 × 10 −6 mbar and 1.29 × 10 −5 mbar oxygen partial pressure, the films lost perpendicular magnetization rapidly and became paramagnetic. Below this range, oxygen had no effect on the perpendicular magnetization of the films.

Domain observations of a durability tested TbFeCo magneto-optical disk using magnetic force microscopy

Complex magnetic structures were observed on a durability tested TbFeCo magneto-optical disk. By considering the magnetic properties of the TbFeCo and the polarized microscopic image of the same region, it was concluded that those complex structures result from the decrement of the compensation temperature of the TbFeCo film at the track center. Samples that were exposed to static magnetic fields were also observed for the purpose of inspecting the changes in the coercive force of the damaged regions.

STRUCTURAL ANALYSIS OF AMORPHOUS TbFeCo ALLOY USING EXAFS FOR PERPENDICULAR MAGNETIC ANISOTROPY

A structural analysis of amorphous TbFeCo films has been performed by using EXAFS of as-deposited and annealed samples. It is found that the numbers of inplane Fe-Fe (and Fe-Co) pairs for as-deposited TbFeCo are larger than in the perpendicular direction. On the other hand, in the case of the annealed samples, the number of in-plane Fe-Fe pairs is smaller than in the perpendicular direction. Thus, the direction of the structural anisotropy of the TbFeCo film changes 90 degree due to the annealing procedure. However, the direction of the perpendicular magnetic anisotropy of the TbFeCo does not change before and after the annealing procedure.

保護被覆付TbFeCo光磁気記録膜の水溶液環境中における腐食挙動

Corrosion behavior of sputter-deposited TbFeCo magneto-optical recording films with protection coating has been studied in an aqueous solution. Specimens having Si3N4 (0∼234 nm)/Tb0.33Fe0.48Co0.19 (74 nm)/glass structure were prepared and an immersion corrosion test and an electrochemical impedance measurement of the specimens were performed in 1.0 kmol·m−3 Na2SO4 of pH6.30.The corrosion morphology of the specimens in the solution was pitting, which started from pinhole defects in Si3N4 protection films. The morphology changed with the thickness of the protection films. The selective dissolution behavior of alloying elements in TbFeCo films into the test solution also changed with the thickness of the protection films.Electrochemical impedance diagrams changed with the progress of pitting corrosion on the specimens. After an analysis using an electrical equivalent circuit of the corroding system, the values for the charge transfer resistance and the relaxation coefficient were found to decrease with the growth of pitting corrosion.

DOMAIN WALL PINNING IN AMORPHOUS TbFeCo FILMS ON PATTERNED SUBSTRATES

Magnetization reversal in amorphous TbFeCo films on patterned glass substrates was studied. Two types of patterns were examined: grooves and square patches. Pinning of the domain walls at the side-walls of the patterns was observed. The pinning depends on the depth of the patterns and the angle of the side-walls: greater depth and steeper side-wall produce stronger pinning. Thermomagnetic recording experiments confirm the ability of patterned substrates to confine recorded domains within boundaries defined by the side-walls.

STUDY OF DOMAIN FORMATION MECHANISM IN MAGNETO-OPTICAL MATERIALS USING MICRO HALL EFFECT MEASUREMENTS

A method for analyzing the dynamics of domain formation in magneto-optical recording media was established using measurement of the extraordinary Hall effect. A magnetic domain was written on a cross-shaped magneto-optical film having an area of 3.4×3.4 μm2 at the center of the cross, and the extraordinary Hall voltage was monitored during thermomagnetic writing. Two kinds of TbFeCo films were investigated. For RE-rich film, the nucleated domain expands with the expanding Curie disk in the heating process, and then shrinks in the cooling process. For TM-rich film, on the other hand, the domain cannot follow the Curie disk and, therefore, does not appear during the heating process. The domain in this case is formed in the cooling process and does not show any tendency to shrink.

MAGNETIC AND MAGNETO-OPTICAL PROPERTIES OF PrGd/FeCo MULTILAYERS

PrGd/FeCo multilayers prepared by the rf sputtering method exhibit perpendicular magnetic anisotropy Ku enhanced by the multilayer (ML) structure. The largest value of Ku obtained is about 30×104 J/m3 at a bilayer period of 1 nm with Pr composition at around 35at. % in rare earth layers and Co composition at 10at. % in transition metal layers. The figure of merits of magneto-optical effect, is 20 to 30% larger than conventional TbFeCo films at the wavelength of 400nm. From the analysis of low angle X-ray diffraction, the relationship between the enhanced anisotropy and the ML structure is discussed.

Thermomagnetic recording in amorphous TbFeCo films on patterned substrates

Magnetization reversal and thermomagnetic recording in amorphous TbFeCo films on patterned glass substrates were studied. Two types of patterns were examined: 1/spl times/1 /spl mu/m/sup 2/ raised and lowered square patches. Pinning of the domain walls at the side-walls of the patches was observed. Thermomagnetic recording experiments confirm the ability of patterned substrates to confine recorded domains within boundaries defined by the side-walls.

Coercivity mechanism in (Co/Pt) and (Co/Pd) multilayers

The coercivity mechanism of multilayer (Co/Pt) and (Co/Pd) is discussed based on the phenomenological micromagnetic theory and the magnetic relaxation treatment. Based on the micromagnetic theory, the pinning size of the order of a few /spl Aring/ is found for both (Co/Pt) and (Co/Pd), but about 100 /spl Aring/ for an amorphous TbFeCo film. On the other hand, the magnetic relaxation approach estimates the Barkhausen volume of the order of 10/sup -18/cm/sup 3/ for these multilayers.

Optical and magneto-optical constants of Pr substituted TbFeCo films

Optimization of tri- or quadrilayer magneto-optic recording media requires knowledge of the optical and/or magneto-optical constants for all of the individual active or passive layers that together comprise the complete disk structure. The optical (n+ik) and first-order magneto-optical (Q1+iQ2) constants for two series (i) (Tb23Fe72.5Co4.5)100−xPrx, (ii) (Tb27Fe65Co8)100−xPrx of Pr substituted TbFeCo films, for which x varies between 0 and 30, have been determined by a combination of ellipsometry and Kerr polarimetry. Ellipsometry has also been used to determine independently the optical constants of the optimized SiN passivation layers developed to protect these samples. Using constants determined experimentally on thick samples, the variation of the polar Kerr rotation and ellipticity as a function of magnetic film thickness has been calculated for light incident from both the air and substrate side of a typical trilayer magneto-optic disk structure in which material from the above series, the magnetic and thermomagnetic properties of which have been previously reported [Carey et al., J. Magn. Magn. Mater. (to be published)], forms the active storage layer. The agreement obtained with measurements demonstrates the self-consistency of the modeling process and the validity of the determined constants.

Write/erase cyclability of TbFeCo for mark edge recording

Domain size changes due to thermal relaxation after high laser power irradiation on amorphous TbFeCo films were studied. In order to achieve mark edge recording for high-density magneto-optical memory, accurate domain size recording is required even after a million erase/write cycles. Highly accelerated erase/write test was performed on typical recording media, rare-earth (RE) -rich and transition-metal (TM) -rich disks. The elongation of the domain size written on the TM-rich film after erase/write cycles was clearly evident; however, the change in the domain size of RE-rich films was small. The small domain size change of the RE-rich disk can be explained in terms of the rapid increase in the coercive force with decreasing temperature and the smaller domain-wall driving force at recording temperature than those for the TM-rich disk, even though both have the same level of structural relaxation.

Effect of grooves on magnetization reversal in amorphous TbFeCo thin films

We have investigated the effect of grooves milled by argon ions in soda lime glass substrates on the magnetic behavior of amorphous TbFeCo films deposited onto these substrates. The domains are shown to expand along the grooves when the groove depth exceeds 10 nm. The effect originates from the difference in the coercivities of the film on the land and on the groove, as well as from the pinning of domain walls by the side-walls of the grooves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thickness dependence of magneto-optic effects in TbFeCo film

The thickness dependence of the coercivity of RF-sputtered amorphous TbFeCo films prepared with the same sputtering conditions has been investigated by using Faraday rotation measurements. From the use of a special STRATA mathematical method to improve EPMA it is confirmed that the composition is thickness independent and the coercivity change is correlated to the variation of the local pinning force induced by the evolution of the morphology from fine to coarse structure by increasing the film thickness.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Angular distribution of the sputtered atoms from TbFeCo targets

The angular distribution of the sputtered Tb, Fe, and Co atoms from the elemental targets could be described by cosn θ distribution with n=1.90, 0.54, and 1.01 for Tb, Fe, and Co, respectively. For TbFeCo composite targets with mixed elemental and intermetallic compound phases, the overall angular distribution of the sputtered Tb, Fe, and Co atoms from the mixed phases could also be described by the cosn θ distribution function, and the values of the n’s were related to the volume percentage of the intermetallic compound content in the composite target. This was not true of the Tb distribution for a target containing high intermetallic compound content. In that sample, an off-normal term has to be added to the cosn θ distribution function. It was found that a composite target with about 23 vol % intermetallic compound would produce a uniform composition distribution of TbFeCo film on the substrate.

The magnetic and magneto-optical properties of amorphous (TbFeCo) Pr films

Amorphous TbFeCo films have been manufactured with a rotating substrate, multi-target, dc magnetron cosputtering process. The light rare earth praseodymium (Pr) has been doped into these TbFeCo alloys in an attempt to increase the intrinsic polar Kerr rotation. Magneto-optical measurements however, indicate a degradation of the Kerr rotation with Pr content in the new alloys. The deterioration of the magnetic properties, the coercivity, the squareness of the hysteresis loop shape and the perpendicular anisotropy are also shown to be a result of Pr substitution.

AIN films prepared with facing target type sputtering method

AIN films were prepared with a new four-pair facing target type sputtering method at a low substrate temperature. The composition x of the AI x N films had a close relationship with the AI target sputtering current ( I AI) and the substrate bias ( V b). When I AL = 200 mA and V b = −90 V stoichiometric AIN films were obtained and the deposition rate was about 140 Å min −. The substrate temperature was lower than 80°C during sputtering. The AIN films prepared under these conditions were in an amorphous state. Without breaking the vacuum the AIN films were deposited consecutively onto magneto-optical TbFeCo films which were also prepared with this four-pair facing target type sputtering method. The AIN films could also enhance the Kerr rotation angle θ K .