Orientation Ratio Research Articles

Quantitative analysis of magnetization reversal in Ni thin films on unpoled and poled (0 1 1) [PbMg1/3Nb2/3O3]0.68–[PbTiO3]0.32 piezoelectric substrates

The field angle dependence of the magnetization reversal in 20 nm thick polycrystalline Ni films grown on piezoelectric (0 1 1) [PbMg1/3Nb2/3O3]0.68–[PbTiO3]0.32 (PMN–PT) substrates is analysed quantitatively to study the magnetic anisotropy induced in the film by poling the piezosubstrate. While the PMN–PT is in the unpoled state, the magnetization reversal is almost isotropic as expected from the polycrystalline nature of the film and corresponding to an orientation ratio (OR) of 1.2. The orientation ratio is obtained by fitting the angular dependence of normalized remanent magnetization to an adapted Stoner–Wohlfarth relation. Upon poling the piezosubstrate, a strong uniaxial anisotropy, whose hard axis is oriented along the [1 0 0] direction of the PMN–PT, is induced, yielding an OR of 3.1. The angular dependence of the coercivity for the poled state is found to consist of a strong increase for increasing field angles away from the easy axis direction and of a sharp decrease for angles close to the hard direction. It is best described by a two-phase model, implying that the magnetization reversal is determined by both, coherent rotation of the magnetic moments, according to the Stoner–Wohlfarth model, and the gradual displacement of the domain walls in obedience to the Kondorsky model.

Effect of orientation on the thermal stability in advanced metal particulate tapes

The effects of the degree of particle orientation on the normalized magnetization decay and activation volume (Vact) were investigated for advanced data recording tapes prepared from ultrafine metal particulate (MP) composite. In this study, the mean volume of particles (Vphy) for advanced MP tapes varied between 1.7 and 5.3×10−18cm3, inclusive of a surface oxide layer. In MP tape with a larger Vphy (=5.3×10−18cm3), increasing the orientation ratio (OR) for improved recording characteristics was found to decrease the normalized magnetization decay. However, the OR values had little effect on the normalized magnetization decay of MP tape with a smaller Vphy (=1.7×10−18cm3). This may be attributed to the existence of a few particles approaching the theoretical superparamagnetic limit of 0.7×10−18cm3. In order to decrease the normalized magnetization decay, it is particularly important to increase Hc, which improves the anisotropy constant and the distribution of anisotropy field (HA) for advanced data recording tapes with very small Vphy. The value of Vact in the low reverse field, which is a major factor affecting media noise, decreased as OR increased regardless of Vphy. Also, Vact of both tapes decreased as the reverse field decreased in the range of 1.2kOe or less. Vact of an assembly of ultrafine particles was dependent on the distributions of HA and volume of particles, also the value of rotational hysteresis integral that related to the deterioration in the mechanism of magnetization reversal giving rise to an incoherent rotation.

Effect of texture vehicle and diamond on SNR and surface topography of media

The mechanical texturing process is that which is utilized to generate circumferential texture patterns on the NiP surface using a pliable tape while supplying a lubricant and diamond slurry. We investigate the texture surface roughness, texture parameter δ/ λ, texture scratch defects, orientation ratio (OR) and signal to noise ratio (SNR) performances of disks prepared by three combinations of thermally heat-treated diamond (THT) and ultra-dispersed diamond (UDD) with coolants labeled A1 and M1. Experimental results show that the substrates textured with UDD/M1 slurry can create a disk surface with the highest parameter δ/ λ, which results in the highest OR and SNR, as compared to substrates textured with THT/A1 and THT/M1 slurries. By increasing the texture coolant concentration from 5 to 25%, the zeta potential, diamond size, texture roughness, texture scratch pixel count, parameter δ/ λ, OR and SNR increase dramatically. The UDD diamond and 10 wt% M1 coolant showed the best performance with respect to lower surface finish ( Ra), lower scratches and higher SNR.

Bis(μ-3,5-dinitrosalicylato)hexaimidazoledicadmium(II) dihydrate

The title dinuclear complex, [Cd2(C7H3N2O7)2(C3H4N2)6]·2H2O, lies about an inversion centre. Each CdII atom is coordinated by three O atoms from two 3,5-dinitro­salicylate ligands and the N atoms of three imidazole ligands. Three ligand O atoms and one N atom lie in the equatorial plane with the two other imidazole ligands axial in a distorted octa­hedral coordination environment. The intramolecular Cd⋯Cd separation is 3.906 (4) A. In the crystal structure, a supra­molecular network forms through extensive inter­molecular hydrogen-bonding inter­actions. One imidazole ring is disordered over two orientations in ratio of approximately 0.8:0.2.

Relation between interface stress in the seed layer and the orientation ratio of longitudinal media

The orientation ratio (OR) is a key issue to achieve high density in longitudinal recording media. Recent recording media have seed layers which exclusively promote small grain growth of the recording layer. In this paper, the effect of seed layers on OR was investigated by the use of various seed materials deposited twice. OR tends to decrease as the thickness of the seed layer is increased; however, the degree of decrease is quite different with seed material. A seed material with small Young’s modulus is preferable for a large OR. These results suggest that OR depends on the interface stress which is relieved as seed layer thickness is increased. Moreover, the relation between the stress in the seed layer and OR was also considered with a multilayer model.

Effects of media orientation on noise, track width, and thermal relaxation

A set of longitudinal antiferromagnetically coupled media with different orientation ratios (OR) was used to study the dependence of recorded data on OR. The OR dependence of dc and transition noise was investigated using a position-dependent time-domain technique. It is shown that both dc and transition noise decrease for a higher medium OR. A model for the dc erase noise power dependence on OR is developed. We will demonstrate that a medium with lower OR has a larger baseline shift and larger effective track width due to an increased cross-track magnetization component at the track edges. A strong dependence of media relaxation time on medium OR was discovered with slower decay rates for higher OR media. These slow relaxation times give rise to anomalous track profiles with track tails extending over 2 microns away from the track center.

Time-domain study of microtrack structure and artifacts

To study the microtrack signal, noise and track “skirts” a time-domain technique [A. Taratorin, M. Xiao, and K. Klaassen, IEEE Trans. Mag. 40, 129 (2004)] was used. It shows that the standard microtrack preparation (two-sided dc erasure) suffers from demagnetization caused by the write head fringe fields. Low density micro-track tail signals were studied by analyzing read-back wave forms at different offset locations from the microtrack center. It was established that the tail-related signal is generated by cross-track medium magnetization. The dependence of this tail signal on the medium orientation ratio (OR) is studied; the tail signal amplitude decreases for higher OR media. An improved microtrack preparation procedure is presented, using two-sided multiple-pass repetitive dc erasure. It is demonstrated that the procedure reduces the tail artifacts due to the smaller cross-track component of the far-away write head field

Effect of diamond types on textured surface morphology and magnetic performance in hard disk

It is well known that hard disk drive media with high orientation ratio (OR) has higher SNR and better thermal stability, which is desirable for higher density recording. The oriented media requires a mechanical texturing process on NiP-plated Al-substrates. Mechanical texturing process is a process to generate circumferential texture patterns (grooves) on the NiP surface using tape with diamond slurry rotating the disk while contacting of the tape and slurry. In this study, we compare the texture parameter δ/ λ, where δ is the average depth of the texture line and λ is the average distance between two texture lines, line density (LD), orientation ratio (OR), and recording performances of disks prepared by three types of diamond slurries, namely mono-crystalline diamond (MD), poly-crystalline diamond (PD), and poly-mono-crystalline diamond (Hybrid). Mono-crystalline diamond slurry is a single crystallite, which has sharper edges and fewer facets. Poly-crystalline diamond slurry contains many single crystallites, which has more rounded edges and facets. Hybrid-crystalline diamond is formed from milled (and rounded) mono-crystalline diamond, using atmospheric and temperature changes to micro fracture the surface of the mono-crystallite structure, producing a harder nucleus and more and sharper cutting facets as compared to poly-crystalline diamond. Experimental results show that the substrates textured with hybrid-crystalline diamond slurry can create disk surface with the highest line density and δ/ λ, which results in the highest OR, the lowest intergranular exchange coupling energy, the lowest DC erase noise, and the highest SNR, than the substrates textured with mono-crystalline and poly-crystalline diamond slurries. With increasing the texture parameter δ/ λ from 0.034 to 0.058, an OR increases from 1.48 to 1.82 and the SNR increases from 19.10 to 19.66. There are very well correlations among δ/ λ, OR, and SNR.

Performance Comparison Between Conventional and AFC Media at Different Orientation Ratios

Antiferromagnetically coupled (AFC) media and conventional media (CM) were compared side to side over a wide range of orientation ratios (OR). For both AFC and CM, oriented media outperform isotropic media. AFC and CM show similar signal-to-noise ratios (SNR) throughout the entire range of OR. CM exhibit good SNR performance even at M/sub r/t<0.33 memu/cm/sup 2/ but with unacceptable thermal decay. When the coercivity is increased to match that of AFC at M/sub r/t<0.30 memu/cm/sup 2/, the SNR of the CM deteriorates and the thermal stability is still worse than the AFC. AFC offers some advantages in SNR roll-off in the isotropic media but not in the highly oriented media.

Transition and DC noise characteristics of longitudinal oriented media

Transition and DC noise characteristics of longitudinal recording media were studied as a function of orientation ratio (OR). With increasing OR, a substantial decrease of DC noise is observed against the gradually increasing transition noise, resulting in the reduced media total noise. The increase in the media transition noise with OR is attributed to the increase in the cross-track correlation length s. The experimentally estimated s for the media with OR=1.8 is significantly larger than that of the media with OR=1.25, possibly resulting from the difference in magnetostatically coupled Co grains aligned to the track direction. For high-density low M/sub r/t designs, reducing DC noise by increasing OR, in spite of an increase in transition noise, becomes an effective means to increasing areal density.

Oriented longitudinal media on glass substrates

This paper reports on the recent breakthrough of achieving high orientation ratio (OR) on directly textured glass substrates. The authors show the necessary structural conditions to obtain OR on glass substrates. They present a unique design of a medium structure including a seedlayer, an underlayer, and an antiferromagnetically coupled magnetic structure. Such a structure gives rise to a high OR and leads to improved recording performance. In particular, the authors show the significant low-noise benefit of the oriented media with narrow recording heads. This technology has enabled the extension of glass disk media to ultrahigh density longitudinal recording.

Dynamic orientation ratio in longitudinal recording media

The origin of orientation ratio (OR) in longitudinal recording media has been controversial in the literature. In the past, the observation of a higher OR for thinner magnetic films has been attributed to stress or thermal effects. Our measurements, carried out over a larger range of time scales, confirm that the thermal effects play a major role in the observation of a higher OR for thinner magnetic films. We point out that the OR is dynamic and follows a ln(t) behavior at larger time scales (5–1000 s). Our studies indicate that a larger OR and a more dynamic behavior of OR will be observed when KuV/kBT values are smaller. We also propose that the slope of dynamic OR can be used to compare the recording performance of media indirectly.

Highly in-plane oriented CoCrPtB longitudinal media for 130-Gb/in/sup 2/ recording

A recording density of 130 Gb/in/sup 2/ was achieved using thermally stable conventional CoCrPtB longitudinal media. The high in-plane orientation ratio (OR) of the media resulted in an excellent recording performance due to a narrow switching field distribution as well as a high thermal stability caused by narrow energy barrier distribution. The low noise is attributed to the fully isolated fine grains with a narrow size distribution. A good in-plane c axis crystallographic texture was achieved by using an optimum multilayered structure of underlayer and magnetic layers. A detailed study of high OR media is reported by characterizing the magnetic, microstructural, and read/write properties.

Thermal effects and in-plane magnetic anisotropy in thin-film recording media

The effect of thermal activation on the in-plane magnetic anisotropy [measured as orientation ratio (OR)] of granular longitudinal magnetic recording media is investigated. Temperature and time dependent studies were made on media with different magnetic layer thicknesses. We find that OR is independent of temperature for a stable medium but shows a large increase with temperature for thermally unstable media. At low temperatures and high field sweep rates, the OR values are found to be the same, independent of the magnetic layer thickness. The unique value when thermal activation is reduced is consistent with the high population of the cobalt c axes along the texturing direction as the origin of anisotropy.

Effect of crystallographic orientation dispersion on media thermal stability and recording characteristics

We have studied thermal stability and recording characteristics of CoCrPtB alloy media with varying c axis anisotropy dispersion, preferred orientation (PO), and in-plane orientation ratio (OR) on both glass and NiP-plated Al substrates. With increasing in-plane c axis orientation and OR, improved recording performances such as lower pulsewidth, lower media transition noise, and lower dc noise are achieved. Thermal decay rate is primarily determined by Co anisotropy dispersion and in-plane OR for the same coercivity media. Media having a large out-of-plane c axis component exhibit a wide switching field distribution and have a high signal decay rate. The PW/sub 50/ and dc noise of media with out-of-plane Co grains are very sensitive to changes in write field. On the other hand, highly oriented media having high OR are less sensitive to head writability variations and offer good thermal stability with excellent recording performance.

Systematic study of in-plane magnetic anisotropy in CoCrPtB/Cr media

Circumferential texturing in longitudinal recording media induces in-plane magnetic anisotropy. It is characterized by orientation ratio (OR), which is an important parameter affecting media performance. Our work shows that among the media with different OR values (including isotropic media with OR=1), the ones with higher OR have both better thermal stability and better recording performance. Therefore, it is important to have a better understanding of the mechanism for in-plane anisotropy so that OR can be further increased. Several mechanisms for in-plane anisotropy have been proposed through micromagnetic analysis or empirical methods. A systematic study of OR in CoCrPtB/Cr media was performed to explore the mechanism of in-plane magnetic anisotropy. Circumferential texture roughness has the most effect on OR, but OR is also strongly affected by magnetic alloy composition and sputtering process parameters such as substrate temperature, underlayer thickness, and magnetic-layer thickness. Higher substrate temperature, thinner underlayer thickness, and thinner magnetic-layer thickness all lead to higher OR. These results suggest that the in-plane magnetic anisotropy comes from stress anisotropy via the inverse magnetostriction effect. The stress is induced at the magnetic-layer/underlayer and underlayer/substrate interfaces, while the anisotropy is suggested to arise from the topology of the circumferential texture lines.

Effects of plasma etching on orientation ratio for longitudinal recording media

Studies on the effects of rf plasma etching treatment on textured NiP/Al substrate on the properties of CoCrTaPt/CrMo longitudinal recording media were carried out. The dependence of coercivity (Hc), coercivity orientation ratio (OR), and disk surface roughness (Ra) on etching parameters, i.e., etching time, pressure, and power, were presented. It was found that by optimizing the etching process parameters, an increase of Hc and OR and a decrease of Ra could be achieved. It was observed that good preferred orientation is necessary for obtaining high OR. The increase of OR could be attributed to the cleaning effect or surface modification by the rf plasma etching treatment on the textured substrate.

Recording characteristics and thermal stability comparisons between antiferromagnetically coupled and conventional media (invited)

We report on the recording performance and thermal stability of antiferromagnetically coupled (AFC) media with varying top and bottom layer thickness as compared with those of highly oriented conventional longitudinal recording media. AFC media offers the expected merit of low Mrt designs such as narrow pulse width (PW50), while maintaining good thermal stability. However, the magnetostatic field resulting from thicker total magnetic thickness in AFC media results in poor overwrite (OW) and a degradation in nonlinear transition shifts (NLTS). Thermal stability of AFC media is mainly determined by intrinsic coercivity of the top layer plus the AF exchange field and the magnetostatic field acting on the top layer through a Ru layer. Low noise conventional media with high orientation ratio (OR) can be produced with an acceptable thermal decay equivalent to AFC media at Mrt values above 0.25 memu/cm2.

Magnetic Coating Thickness Influence on the Texture in Metal Particle Systems

The magnetic characterization of four experimental advanced double-coated MP tapes with different magnetic coating thickness has been completed. Although standard vibrating sample magnetometer (VSM) measurements show very similar characteristics such as coercivity, squareness and orientation ratio (OR), alternative measurements show distinct differences in addition to their magnetic thickness. The in-plane distribution of easy axes (EAD) measured using a bi-axial VSM, show that the distribution width increased as the magnetic coating thickness decreased. A theoretical relation between OR and EAD was used to determine the out-of-plane distribution width. This was found to be narrower than the in-plane equivalent, as expected. The out-of-plane distribution width decreased as the magnetic thickness decreases, contrary to the in-plane variation.

Micromagnetic study of anisotropy sources in textured longitudinal media

Micromagnetic simulations were performed to determine the effects of three anisotropy sources on the orientation ratio (OR) in circumferentially-textured longitudinal recording media. Models of the Co c-axis distribution, disruption of the magnetic coupling due to the texture lines, and stress anisotropy were used to generate hysteresis loops in both parallel and perpendicular directions. Parameters were obtained from experimental measurements. Of these three anisotropy sources, a preferential alignment of the Co c-axis along the grooves produces the largest OR; disruption of the magnetic coupling yields a smaller OR value, but leads to the perpendicular loop closing outside the parallel loop. Although the stress anisotropy increases the coercivity in both directions, the OR is the smallest. A combination of these three anisotropy sources, as well as a weak intergranular exchange, leads to agreement with the experimental measurement of OR.