In-plane magnetic anisotropy can be induced in Cr-underlayer/Co-alloy thin films by grooves or scratches in the substrate. To quantify this effect, silica substrates have been prepared with large areas of submicron grooves using interferometric lithography. The growth of Cr films and Cr/Co-alloy bilayer films on these substrates has been investigated, and in-plane magnetic anisotropy has been observed.

The effects of sputtering argon pressures and sputtering power on the microstructure, texture and magnetic properties of NiAI underlayers on CoCrPt films were investigated. In this paper, the relationship between the sputtering conditions, microstructure, crystallographic texture and magnetic properties of these thin films will be discussed. By controlling the sputtering pressure and sputtering power, the texture and microstructure of NiAI underlayers were found to vary. This in turn was found to influence the magnetic properties of CoCrPt thin films. It was found that 10 mtorr is the optimum pressure to deposit the NiAl thin films to obtain the best magnetic properties for our system. At this argon pressure, the coercivity reached a maximum value because of the strongest CoCrPt (1010) texture and smallest grain size. At lower argon pressures (< 10 mtorr), NiAI tended to have a (110) texture reducing the CoCrPt (1010) texture, which in turn reduced the CoCrPt coercivity and S*. Also, high NiAl deposition pressures (>30 mtorr) yielded larger grains and a weaker CoCrPt (1010) texture, thereby decreasing the coercivity of the CoCrPt films. Increasing the sputtering power has been found to increase the CoCrPt coercivity and S* value. However, the grain sizes of the CoCrPt/NiAl thin films deposited at higher sputtering power were larger than those obtained at lower sputtering power.

Reliable core-loss spectroscopic methods have been developed for mapping elemental segregation in Co-Cr-X magnetic recording media by energy-filtered transmission electron microscopy. Extraction of quantitative compositions at a spatial resolution approaching 1 nm involves sophisticated treatments for diffraction contrast, variations in specimen thickness, and closely-spaced oxygen K and chromium L23 ionization edges. These methods reveal that intergranular chromium levels are ∼25 at.% for random-angle boundaries and ∼15 at.% for 90° boundaries in films of Co84Cr12Ta4 d.c. magnetron sputtered at 250°C.

The current study of CoCr12Ta4/Cr longitudinal recording media combines high resolution electron microscopy (HRTEM) with nanoprobe energy dispersive spectroscopy (EDS) and energy-filtered imaging (EFTEM) to correlate the Cr distribution with specific microstructural features. EFTEM images show Cr enrichment at grain boundaries, both random angle boundaries and 90° bicrystal boundaries. Cr segregation within grains is also observed in the elemental maps. This intragrain segregation often occurs at a series of defects that may define separately nucleated grains having 00 misorientation. Nanoprobe EDS measurements indicate that these defects contain localized concentrations of 25 to 30 % Cr. The random angle grain boundary Cr concentration occurs with a wide range, 19 to 36 at% (mean 22%) whereas the more crystallographically related 900 boundaries contain less Cr with less variation, 15 to 21 at% (mean 17% Cr). Composition profiles across grain boundaries using both nanoprobe EDS and EFTEM images show the full-width-half-maximum of the segregation to be approximately 4 nm, with Cr depleted regions next to the grain boundary having less than 7 at% Cr. The Ta concentration revealed no statistical evidence of segregation.

In this study, we examine the effects of introducing CrMn as an intermediate layer between the NiAI underlayer and the CoCrPt magnetic layer, and as an overlayer on top of the Co-alloy film. The effects of deposition temperature and post-deposition annealing on the texture and magnetic properties were studied. Post-deposition annealing effectively lowered the exchange coupling between grains, increased the coercivity by 38%, up to 4600 Oe, and moderately decreased the Ms by 15%. Interlayer diffusion of CrMn into the CoCrPt grain boundaries is believed to cause the change in magnetic properties. It was also found that granular exchange coupling seems to be correlated to the Co-alloy in-plane texture.

The effects of rapid oxidation and overcoat diffusion processes on the intergranular coupling and grain isolation in thin Co films were studied. The oxidation process was found to be strongly temperature dependent. The optimal coercivities can only be achieved within a narrow range of temperatures, while further increasing the temperature incurs significant thermal instability. CrMn underlayers were confirmed to be more effective in enhancing the grain isolation by the grain boundary diffusion during the oxidation process. The oxidation process does not change the Co anisotropy, and hence the coercivity increase is appears to be a result of better grain isolation. The in-situ diffusion of Ag and Cr overcoats were also found to have siginificant effects on the grain isolation in Co and CoCr films.

In this overview paper the concept of thermal activation of magnetisation reversal is reviewed in terms of the Wohlfarth-Gaunt formalism. This formalism gave rise to the concept of an activation volume of reversal. Other techniques have been developed for the determination of activation or critical volumes of reversal and these are reviewed. It is found that these methods give the same approximate value for the activation volume but the only method based on micromagnetism is the waiting time experiment which is consistent with Gaunt. Factors which affect the activation volume such as incoherent reversal and intergranular coupling are discussed together with measures that may be required in order to generate ultrahigh density recording media that are relatively free from thermal loss of signal.

Elemental segregation of CoCrTa and CoCrPt thin films for longitudinal and perpendicular media is investigated using high spacial resolution transmission electron microscopes equipped with compositional analysis facilities. Strong Cr segregation exceeding 20 at% within 1.5-2 nm width is observed along the grain boundaries for both types of CoCrTa films prepared at elevated substrate temperatures. Weaker Cr segregation is observed along the grain boundaries of the longitudinal and the perpendicular CoCrPt films. The strong Cr segregation at grain boundaries is related with the small magnetic cluster size and the low media noise characteristics of CoCrTa thin film media. The Cr content inside the grain is several % lower than the average composition of the CoCrTa films. The magnetocrystalline anisotropy constants(Ku) for different Cr compositions are determined using single crystalline thin film technology to discuss the thermal stability of recorded information.

The thermal stability of written bits in high density longitudinal recording media is investigated using magnetic force microscopy (MFM). The time dependence of the MFM signal is examined for different linear densities on CoCrPt-based media of various thickness. At ambient temperature, lesser decay is observed using the MFM compared to spin stand measurements on the same CoCrPtTaNb media on Al which emphasizes the dependence of bit stability with writing conditions. Moderate anneals at 373 K reveal a rapid initial ∼ 10% signal decay followed by stable behavior not observed in the magnetization time dependence measurements. 200 kfci tracks on a 20-nim thick CoCrPtTa medium on Si with a coercivity of 3 kOe displayed stable (∼ 2%) behavior against a 105-hour anneal at 373 K in air. These results are correlated with media properties to obtain parameters that are good indicators of thermal stability performance.

Thermally induced decay of longitudinally recorded magnetic transitions is measured on a spin-stand. The decay rate increases with increased linear density and decreases with increased media coercivity. A new spin-stand experimental technique has been developed which allows measurements of the time dependence of the media coercivity as a function of write times spanning short times characteristic of write times in drives to long times associated with VSM measurements. The ratio of long to short write time coercivity was larger for media which are thermally unstable.

In this work the effect of grain size and magnetic switching volume on media noise due to intergranular coupling for CoCrTaPt/Cr thin film media deposited at substrate temperature of 160 and 260°C are investigated. The film deposited at substrate temperature of 260°C showed weaker intergranular interaction and lower media noise compared to the film deposited at 160°C. The magnetic switching volume (V*) is an important consideration for thermal stability and media noise in high density recording media. The magnetic switching volume V* for the film deposited at 160 and 260°C was calculated to be 3.7 x 10-18 and 3.2 x 10-18 cm3 respectively. The magnetic switching volume is correlated to the average Co-alloy grain size, media noise and the interactions between the grains.

The effects of DC bias on the thermal stability and magnetic anisotropy of CoCrTa/Cr thin film media fabricated by using a DC in-line sputtering machine is presented in this paper. In sputtering, a negative DC bias voltage, varying from 0 to 400 V, was applied for the CoCrTa layer. The coercivity was observed to increase almost linearly from 1800 to 2300 Oe for negative bias voltage from 0 to 400V. The thermal stability of these media was studied by measuring the time decay of remanent magnetization under various reverse magnetic fields. The maximum value of the magnetic viscosity coefficient, which happens around remanent coercivity of each samples, decreases with increasing substrate bias voltage. This implies an improvement in the thermal stability of the CoCrTa/Cr thin film media. The magnetic anisotropy constants were measured using both a torque magnetometer and a vibrating sample magnetometer. The magnetic anisotropy measured using torque magnetometer decreases, while that measured using the method of the law of approach to saturation was found to be almost constant, with increasing bias voltage. The activation volumes decreased with increasing bias voltage. The magnetic hardness coefficient determined using the law of approach to saturation, indicating the number of in-depth defects in the CoCrTa layer, increased with increasing bias voltage. The internal stress in these films measured using X-ray diffractometer also supported the existence of in-depth defects. The pinning of the rotation of magnetization by these defects in the magnetic grains maybe responsible for the improvement of thermal stability.

We present Monte Carlo and Langevin micromagnetic calculations to investigate thermal switching of single-domain ferromagnetic particles. For the Monte Carlo study we place particular emphasis on the probability that the magnetization does not switch by time t, Pnot(t). We find that Pnot(t) has different behaviors in different regimes of applied field, temperature, and system size, and we explain this in terms of different reversal mechanisms that dominate in the different regimes. In the micromagnetic study of an array of Ni pillars, we show that the reversal mode is an ‘outside-in’ mode starting at the perimeter of the array of pillars.

The field dependence of the rotational hysteresis energy loss was simulated for longitudinal thin-film media with the purpose of examining the validity of this method for measuring the anisotropy field. The field at which the rotational hysteresis vanishes, which is usually taken as the experimentally measured anisotropy field, was found to be smaller than the real anisotropy field when intergranular magnetostatic and exchange interactions are included in the simulations. Hence the rotational hysteresis method may result in an underestimation of the anisotropy field for the films with non-negligible grain interactions. To confirm this experimentally, two CoCrTa films, one with strong in-plane easy axis texture and the other with uniaxially aligned grain easy axes, were prepared under the same conditions. The anisotropy field determined by the rotational hysteresis of the first sample was found to be smaller than the more accurate value obtained from the hard axis hysteresis loop of the second sample.

A Preisach-Arrhenius aftereffect model, that accurately calculates the entire relaxation process, including the linear log-time region, is used to describe some other characteristics of the time decay. The location of the peak of the decay coefficient is shown to be less than the peak of the irreversible coercivity by an amount that is a function of the standard deviation of the critical field, the fluctuating field, and the moving parameter. The model computes a magnetization decay that includes nonmonotonic behavior under certain circumstances, depending upon the applied field history. A conclusion of this paper is that procedures for accelerated testing of magnetic media are suspect.

The very large perpendicular magnetic anisotropy of the order of 2 x 107 erg/cm3 at room temperature was found in CoJ-x Ptx(0<x<0.5) alloy thin films made by e-beam evaporation. The large magnetic anisotropy is likely related to the anisotropic Co-Co bonding distribution, which is similar to the cases of Co/Pt multilayers and FePt alloy thin films. The activation energy estimated for the ordering is approximately 0.3 eV, which is preferably compared to 0.2 eV for FePt. A model is proposed, for which both a short range and long range ordering are present, depending on substrate deposition temperature.

A polarized neutron reflectometry study of the magnetization density depth profile of a Co0.1Pt0.9-CoPt3 bilayer film found evidence for an induced moment in the Co0.1Pt0.9 overlayer in close proximity to the CoPt3 underlayer. If the moment of Co in these films is that of the bulk, then the μpt = 0.09(1)μB in the overlayer, and μpt = 0.04(1)μB, in the underlayer. In addition, ferromagnetic order of the Co0.1Pt0.9 overlayer was observed 8K above Tc for the material in the bulk.

The present paper discusses the magnetic anisotropy and magnetic domain structure of highly ordered epitaxial FePt(001) films grown on Pt seeded MgO(001) substrates. These films were grown by dc-magnetron sputtering from a Fe50Pt50 alloy target at a substrate temperature of 550°C during deposition. Thicknesses were varied between 15 and 170 nm. The presence of the highly anisotropic face centered tetragonal L10 crystal structure with a maximum long range chemical ordering of 95% and a low degree of misorientations was confirmed by specular and grazing incidence X-ray diffraction measurements. For film thicknesses ≥ 50 nm in-plane and out-of-plane hysteresis measurements indicate large perpendicular magnetic anisotropy and at the same time low remanent magnetisation. Magnetic force microscopy reveals highly interconnected perpendicular stripe domain patterns. From their characteristic width, which is strongly dependent on the film thickness, a value of the dipolar length, D0, of 50 ±5 nm is derived. Assuming an exchange constant of 10-6 erg/cm, this value is consistent with an anisotropy constant Ku ∼ 1.108 erg/cc.

Structural and magnetic properties of Co50 ± x Pt50± x films 25-50 nm thick, prepared by molecular beam epitaxy onto a Pt buffer grown on MgO (001) substrate have been investigated. A series of 3 samples with different compositions (x = 6, 0, -6) was grown at 800 K on a 10 nm thick Pt buffer and another series of 5 samples of equiatomic composition was prepared at various growth temperatures (390 K≤ TG≤ 780 K) on a Pt buffer 4 nm thick. X-ray diffraction and TEM studies show the presence of grains with [111] and [002] orientations, the [002] grains being a mixture of the tetragonal L10 ordered phase and of the fcc disordered one. Both the thickness of the buffer layer and the deposition temperature are determinant parameters of the structural quality of the films and of the degree of long range order (LRO). An apparent LRO parameter (ηapp) is deduced from the superstructure and main peak intensity ratio. Its increase with the growth temperature is described through a thermally activated model that yields a small activation energy of 0.28 eV, illustrating the role played by both surface diffusion and surface interactions in building the L10 compound in agreement with theoretical predictions. An average uniaxial magnetocrystalline anisotropy energy (Kuav) is deduced from the magnetization curves measured by a SQUID. The anisotropy energy of the [002] grains (Ku002) is deduced, assuming a linear relationship between the anisotropies and the phase percentages. One observes a continuous but not linear increase of Ku002 with ηapp.

The formation of electrochemically etched, self-organised nanostructures on aluminium enables the production of large area regular arrays in a fast and cost-effective way. These microstructures could form the basis to develop masks for subsequent materials deposition without the need for time consuming patterning techniques.

The desired regular arrays result from a steady state interaction between the electrolyte and samples' surface under the influence of a cell potential. The type of array formed depends on this cell potential and shows an evolution from lines to dots.

Although a gradual progress towards a regular lattice spanning large areas is expected, the presence of initial disturbances of the samples' surface or bulk distorts the final lattice considerably. In this work the modulation depth and type of the resultant nanostructures produced at different cell potentials are assessed in view of practical applications.