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Magnetic skyrmions are promising candidates for computing and memory applications. The static and dynamic behaviors of skyrmions are tunable by altering the interfacial magnetic properties. These interfacial magnetic properties are alterable by modifying the interface structure of thin films. However, the relationship between the structural properties of the interface and the skyrmions properties is not straightforward, and a comprehensive insight is required to facilitate better controllability of the skyrmions' behaviors. Here, we comprehensively understand the relationship between atomic displacements at the interface and skyrmions' static behavior. In this study, we used ion irradiation to achieve inter-atomic displacements. We observed that the inter-atomic displacements could tailor the physical properties of skyrmions. We noticed a peculiar increase in the magnetization, Dzyaloshinskii–Moriya interaction, and exchange stiffness. The modifications in magnetic properties reduced the domain wall energy, which enhanced the skyrmion density (by six-folds) and reduced the average skyrmion diameter (by 50%). Furthermore, we compared the observed results of ion irradiation with those from the annealing process (a well-studied method for modifying magnetic properties) to better understand the effect of atomic displacements. Our study provides a route to achieve a highly-dense skyrmion state, and it can be explored further to suppress the skyrmion Hall effect for skyrmion-based applications. [ABSTRACT FROM AUTHOR]

The magnetic and structural properties of graded media fabricated by ion implantation of nitrogen (14 N+), oxygen (16O+), and cobalt (59Co+) ions in the CoCrPt-SiO2 recording layer of prototype disk have been studied. Ion implantation of the species was controlled at the atomic scale to fabricate the graded media. Magnetometric measurements indicated that the coercivity was reduced with an increasing dose of the implanted species. The observation of an increase in magnetic domain size has been attributed to the reduction in magnetocrystalline anisotropy energy, which is desirable for achieving graded media. The study indicates that the magnetic properties can be tailored by the appropriate selection of the implantation dose and species. [ABSTRACT FROM AUTHOR]

We have used the method of anomalous Hall effect (AHE) to characterize magnetic thin film structures consisting of both perpendicular (normal-to-plane) and longitudinal (in-plane) anisotropies. AHE enables the simultaneous extraction of the perpendicular and in-plane magnetizations. The method is used to obtain the hysteresis loops and study the switching behavior of [Co/Pd] multilayers coupled to different seed layers. Results show that Cu seed layer helps to reduce the switching field distribution (SFD) and increase the coercivity while Co underlayer with an in-plane anisotropy helps to reduce the coercivity and increase the SFD. Furthermore, the magnetization in the Co in-plane layer is found to be pointing out of plane possibly due to exchange coupling with the [Co/Pd] multilayers. [ABSTRACT FROM AUTHOR]

The crystallographic growth, interfacial roughness, and magnetic properties of CoCrPt–SiO2 perpendicular magnetic recording media prepared on various types of Ru intermediate growth layers were systematically investigated based on high angle and omega offset x-ray diffraction scans, rocking curve scans, synchrotron radiation based grazing incidence reflectivity scans, and magneto-optical Kerr hysteresis loops. For samples that make use of one Ru growth layer, voltage bias applied on the Ru layer was seen to have two observable effects: (1) the dispersion in the Ru(00·2) perpendicular texture increased, but that of the Co(00·2) remained unchanged, leading to identical layered growth and (2) the in-plane a-lattice parameter of the Ru decreased leading to enhanced heteroepitaxy with the Co. There was no significant change in the Ru–Co interfacial roughness with changing the bias on the Ru layer. The bias effect can be used to optimize the design of the Ru intermediate layers. A scheme that makes use of two Ru growth layers consisting of a bottom Ru layer prepared under zero bias, which is inserted below a second Ru layer prepared under biased conditions, is shown to lead to significant benefits such as improved texture without affecting the magnetic properties. This is due to the different functional roles ascribed to each of the Ru growth layers. [ABSTRACT FROM AUTHOR]

In this paper, magnetic and structural properties of near-equiatomic CoPt thin films, which exhibited a high coercivity in the film-normal direction-suitable for perpendicular magnetic recording media applications-are reported. The films exhibited a larger coercivity of about 6.5 kOe at 8 nm. The coercivity showed a monotonous decrease as the film thickness was increased. The transmission electron microscopy images indicated that the as fabricated CoPt film generally consists of a stack of magnetically hard hexagonal-close-packed phase, followed by stacking faults and face-centred-cubic phase. The thickness dependent magnetic properties are explained on the basis of exchange-coupled composite media. Epitaxial growth on Ru layers is a possible factor leading to the unusual observation of magnetically hard hcp-phase at high concentrations of Pt. [ABSTRACT FROM AUTHOR]

Magnetic and structural properties of Co80Pt20 films were modified by controlled ion implantation through a dot-patterned mask for possible application in the mass production of patterned recording media. The dot patterns were fabricated using self-assembly of di-block copolymers. The effects of 14N + and 40Ar+ ion implantation at energies as high as 40 and 100 keV, respectively, were studied. Although both ions cause changes in the structural and magnetic properties, 40 Ar+ ion implantation leads to more significant changes. The structural changes, predicted using simulations and experimentally observed using X-ray diffraction, indicate a mixing of Co into the layers below, leading to layers richer in Pt at the top. Magnetic force microscopy measurements show an increase in domain width and domain wall thickness as a function of ion fluences. The results are analyzed with measurements of magnetic anisotropy constant and micromagnetic simulations. [ABSTRACT FROM PUBLISHER]

Microstructural investigations of granular perpendicular recording media based on stacked CoPt-alloy layers were carried out using high-resolution transmission electron microscopy (HRTEM). In the structure investigated, a thin layer of CoPt with high Pt concentration was inserted to meet the thermal stability requirements at higher densities. The increase in the coercivity and nucleation field of the sample observed for the insertion of a thin layer of CoPt (3 nm), and the decrease beyond this critical thickness has been explained based on HRTEM studies. HRTEM results indicated that the insertion of thicker CoPt layer causes stacking faults and the presence of fcc phase in the CoCrPt layers on the top. The number of stacking faults and the fcc content in grains depend on the thickness of CoPt layer, indicating that the observed changes in magnetic properties arise due to the microstructural changes. [ABSTRACT FROM AUTHOR]

Magnetic properties and corrosion inhibition properties of hybrid magnetic overcoats (Hy-MOC) that are suitable for ultra-high-density recording are investigated. Two types of Hy-MOC using different types of Co-based alloys were investigated for the magnetic overcoat (MOC). Hy-MOC (α) used CoCrPt : SiO2 (14% SiO2) while Hy-MOC (β) used CoCr22 as the sputtering targets for the reactive sputtering with N2. Magnetic hysteresis loops indicated that both types of Hy—MOC-using various percentages of N2 flow rate—are coupled with the recording layers of the hard disk media. Hy-MOC also increased the coercivity of the perpendicular media which is attributed to the enhanced thermal stability. It was also found that the remanent squareness (S = Mr/Ms of the media using the MOC was closer to 1. The negative nucleation field Hn of the media using Hy-MOC (α) also showed a slight increase as compared to the medium without Hy-MOC but it is not seen for the media using Hy-MOC (β). Potentiodynamic polarization analysis of Hy-MOC samples also indicated that the Hy-MOC are able to provide sufficient corrosion protection for the hard disk media; and they are as good or even better than 2 nm amorphous carbon overcoat. [ABSTRACT FROM AUTHOR]

Perpendicular recording media, where the recording layer is deposited on carbon-based synthetic nucleation (SN) layers, have been investigated for magnetic and microstructural properties. It was observed that the recording layers deposited directly on low-pressure sputtered Ru layers with and without an SN layer showed a similar microstructure from plan-view TEM images. However, the magnetic properties of the media with SN layer show better intergranular segregation, whereas the media without SN layer show signs of strong intergranular exchange coupling. Recording layer thickness dependent studies indicate that the 3-nm-thick recording layer deposited on the Ru layer directly without SN layer showed rectangular hysteresis loop, indicating the formation of a continuous layer. A recording layer (3 nm) deposited on an SN layer showed a superparamagnetic type of hysteresis loop, indicating better intergranular segregation. Transmission electron microscopy observations also indicate that the recording layer deposited on SN layer shows better segregated structure even at 3 nm. The results indicate that SN layer is beneficial for grain size reduction as well as eliminating the initial continuous layer formed in the recording layer. [ABSTRACT FROM AUTHOR]

Perpendicular recording media, where the CoCrPt-oxide recording layer is deposited on carbon based synthetic nucleation (SN) layers, have been proposed for recording applications and studied using first-order reversal curves for their magnetic interaction behavior. The magnetic properties of media with SN layer show better intergranular segregation whereas the media without SN layer shows otherwise. It is proposed that a dual SN layer structure, where an SN layer deposited above and below the high pressure sputtered Ru layer is suitable for achieving smaller grain size as well as better intergranular segregation. [ABSTRACT FROM AUTHOR]

Current generation CoCrPt oxide based perpendicular magnetic recording media use two Ru-based intermediate layers in order to grow crystallographically textured, and magnetically isolated granular media. In this work, the advantage of replacing the Ru grain isolation layer with antiferromagnetic IrMn is demonstrated. Media samples using 7.5 nm thick IrMn intermediate layers show perpendicular texture with dispersion below 4°, coercivity of over 4000 Oe alongside magnetic exchange decoupling, average grain sizes of 6 nm with distributions under 14%, and thermal stability factor of 88. The IrMn layer may also help to stabilize the recording layer grains against thermal instability effects. [ABSTRACT FROM AUTHOR]

A key objective in the design of recording media for hard disk drives is to tailor the grain size. A fourfold increase in the recording density from the current levels demands that the mean grain diameter be reduced from 7 to about 5.5 nm, and distribution to below 15%. Traditional techniques involving dopants can realize small grain sizes but also deteriorate the structural and magnetic properties. In this study, the utility of an extremely thin synthetic nucleation layer in reducing the grain size and distribution of the recording media is demonstrated, with significant implications for other applications too. [ABSTRACT FROM AUTHOR]

CoCrPt–SiO2 perpendicular recording media containing dual-Ru intermediate layers have been studied. The bottom Ru layer deposited under a higher mobility condition, i.e., low Ar gas pressure and bias on substrate, helps to achieve a good crystalline texture, and the top Ru layer under a lower mobility condition, i.e., high Ar gas pressure, promotes the formation of a columnar microstructure. Three kinds of grain boundaries have been observed. The nucleation field and the coercivity as a function of the thickness and dc bias of the bottom Ru layer have been investigated. Medium noise reduction has been observed for dual-Ru intermediate layer media (dual-Ru media) in comparison with that of single intermediate layer media (single-Ru media). This is mainly attributed to the optimization of the physical grain segregation. [ABSTRACT FROM AUTHOR]

Perpendicular recording media for high areal density face several requirements such as small grain size, high coercivity, and negative nucleation field. Previous studies on increasing the oxygen concentration in CoCrPt:SiO2 media to reduce the grain size indicated that the increase of oxygen flow can lead to undesirable properties such as low coercivity and positive nucleation field. We propose recording media with two or more CoCrPt:Si2 layers to obtain optimum microstructure and magnetic properties. In this study, we prepared CoCrPt:SiO2 media with two magnetic layers and the increase of oxygen flow rate ratio in the bottom layer, up to 2.3% did not lead to a decrease of coercivity or increase of nucleation field. A high coercivity, negative nucleation field, etc., can be observed. The signal-to-noise ratio (SNR) of the recording media increased up to a flow rate of 2.3%. The results indicate that by optimizing the oxygen composition in the bottom and top layers of stacked CoCrPt:SiO2 recording media, recording performance can be enhanced. [ABSTRACT FROM AUTHOR]

Antidots of Co/Pd multilayers with 3-bilayers [(Co/Pd)x3] that were antiferromagnetically coupled(AFC) to (Co/Pd)x10 were fabricated and their magnetic properties were investigated. The thickness of Co in (Co/Pd)x3 was varied from 0.4 to 0.8 nm. Samples with a Co thickness of 0.8 nm in the bilayer showed a perpendicular magnetic anisotropy (PMA) when antiferromagnetically coupled to (Co/Pd)x10. On the other hand, the magnetization direction of single Co/Pd multilayers with thick Co (0.8 nm) as a reference structure (without AFC) was observed to be in plane, indicating that the PMA in (Co/Pd)x3 films with thicker Co is due to the antiferromagnetic coupling. We also carried out a systematic study on this set of thin films patterned in antidot array fabricated using nanoimprint lithography. It was found that the AFC is helpful to induce a perpendicular magnetic anisotropy in both thin film and antidot form. Such a result is interesting both from a fundamental viewpoint and also from their potential applications in spintronics devices and patterned magnetic medium. [ABSTRACT FROM AUTHOR]

In magnetic force microscopy (MFM), it is effective to control the magnetic properties of the coating materials on the MFM tip to achieve higher resolution. In this work, the effect of the magnetic anisotropy of the tip-coating, such as perpendicular magnetic anisotropy (PMA), in-plane magnetic anisotropy (IMA), and random magnetic anisotropy (RMA), on the MFM image resolution are studied by micromagnetics. An accurate 3 D micromagnetic model of the CoPt pyramid MFM tip, with a cone angle of 37°, tip height of 120 nm, coating thickness of 7.6 nm, and average grain size of about 8.8 nm, was setup to calculate the domain structure and the stray field of the tip. A CoPt disk medium, with a bit size of 24 × 32 nm2 and film thickness of 8 nm, was chosen for image simulation. The PMA tip is advantageous in low scan height (SH) measurement with little tip-sample interaction due to its sharp and small stray field, while the IMA tip will disturb the magnetic moments of the medium at a low SH due to its strong stray field, and the RMA tip cannot read the bits with clear image contrast due to its broader field distribution. [ABSTRACT FROM AUTHOR]

High-energy carbon deposition techniques provide thin overcoats with high corrosion and wear protection for magnetic recording media applications. The effect of high-energy (0-300 V substrate bias) deposition on the implantation induced changes in magnetic and structural properties of granular perpendicular magnetic recording media is studied. To observe subtle changes in a thin region of recording media, antiferromagnetically coupled layer structure was used. Clear changes in the magnetic properties, observed as a function of the carbon deposition energy, correlate with other measurements such as X-ray photoelectron spectroscopy, indicating the need to consider such effects when designing media and overcoat. [ABSTRACT FROM AUTHOR]

Review: 53 refs. [ABSTRACT FROM AUTHOR]