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Ferromagnetic resonance measurements can provide valuable information about thin-film structures, including recording media. This paper develops analytic expressions for the behavior of continuous-coupled multilayer perpendicular films and compares these with micromagnetic simulations. A frequency-domain equation is derived for small excitation, where the in-plane variables are expressed as complex quantities. The corresponding micromagnetic simulations implement the standard Landau–Lifshitz–Gilbert equation and are driven with an in-plane linear sinusoidal excitation. A four-layer graded medium is used as an illustrative example. The medium includes a relatively soft, lossy, weakly coupled cap. The analytic result reveals four resonant modes with the lowest mode at 16.40 GHz with zero external dc field. The simulation matches the analytic frequency and damping factor well but only for very low levels of excitation. [ABSTRACT FROM PUBLISHER]

User-programmed meso- to microscale 2D shapes using magnetic nanoparticles as building blocks with magnetic-field-directed self-assembly are created. The assembly templates are magnetically recorded using perpendicular magnetic recording (PMR) media. The results demonstrate that PMR can template user-designed features in two dimensions down to 30 nm in size, i.e., the nanoparticle diameter. It has been also shown that the nanoparticles assemble onto transitions between oppositely magnetized regions in the medium. At these transitions, the magnetic field gradients are extremely large (25 MT m−1 2 nm above the medium) and change rapidly with height (≈1015 T/m/m within 20 nm of the surface). It is found that 30 nm diameter particles assemble into 1-2 layers with feature widths ranging from 30 to 350 nm. It is hypothesized that large lateral growth can occur because the magnetic forces parallel to the disk extend up to 150 nm on either side of a recorded transition, falling off more slowly with distance than the vertical magnetic forces. Once lateral growth saturates, a second layer of nanoparticles begins to assemble on top of the first layer, suggesting strong potential for controlling layer-by-layer assembly through appropriate design of the medium and its resulting field gradient profiles. [ABSTRACT FROM AUTHOR]

The microstructures and magnetic properties of FePt(-SiO{x}-C) thin films grown on TiON and TiON/TiN intermediate layers were studied. TiON possessed smaller surface energy and smaller lattice constant than TiN. With increasing TiO{x} doping concentration, FePt grain shape changed from semi-spherical to square and grain size was significantly reduced. Meanwhile, good perpendicular magnetic anisotropy was retained, indicating that TiON intermediate layer could achieve a good balance between island growth and epitaxial growth. Furthermore, using TiON/TiN combined intermediate layer, FePt grain size was further reduced and the opening-up of in-plane M–H loop diminished. With 45 vol.% SiO{x}-25 vol.% C doping, well-isolated FePt grains with an average size as small as 5.7 nm and the grain size distribution of 0.9 nm were achieved. It also exhibited good perpendicular magnetic anisotropy with an out-of-plane coercivity of 18 kOe. [ABSTRACT FROM PUBLISHER]

The effects of a TiN intermediate layer on the microstructure and magnetic properties of the FePt films were investigated. It was found that the TiN layer could effectively block the diffusion of Cr into the FePt film. The good epitaxial relationships among these layers were revealed from the transmission electron microscopy (TEM) results. With introducing TiN intermediate layer the chemical ordering and magnetic properties of FePt films significantly improved. The FePt film with 5 nm TiN exhibited a high perpendicular coercivity of 13.7 kOe and a low in-plane coercivity of 0.24 kOe, resulting from the combined contribution of TiN (200) orientation, TiN layer roughness and the effective block of Cr diffusion. Moreover, with doping C into the FePt-SiNx films, the out-of-plane coercivity increased due to the decrease of the exchange coupling, the grain size of FePt films decreased, and well-separated FePt grains and uniform size were formed. By optimizing the sputtering process, the [FePt (4 nm)-SiNx 40 vol\cdot\\%]- 20 vol\cdot\\% C (001) film with coercivity higher than 21.5 kOe, a single layer structure, and small FePt grain size of 5.6 nm in average diameter was obtained, which are suitable for ultrahigh density perpendicular recording. [ABSTRACT FROM AUTHOR]

Abstract: Granular L10 FePt (001) thin films were deposited on a Si substrate with Ta/MgO underlayers by rf sputtering. The effects of in-situ heating temperatures (350–575°C), pressures (2–40mTorr), and sputtering powers (15–75W) on texture and microstructure were investigated for the FePt films. We obtained films with grain densities approaching 50teragrains per in.2, grains sizes down to 2.2nm with center-to-center spacing of 4.2nm and coercivity of 24kOe. The order parameters for the L10 FePt thin films were derived and calculated to be as high as 0.91. Although the grain size is small, the spacing between grains is too large for practical heat assisted magnetic recording media. To reach the desired results, we propose that layer-by-layer growth should be promoted in the FePt layer by inserting another underlayer that provides a better lattice match to L10 FePt. [Copyright &y& Elsevier]

We present an experimental approach for obtaining highly ordered L10 FePt-oxide thin film media with small grains by using a RuAl layer as a grain size defining underlayer. In most previous studies, the FePt grain size was controlled by tuning the oxide volume fraction of the film. By introducing the RuAl grain size defining layer, 6 nm of FePt grains can be obtained at 520^\circ\C with 9% \SiO2 in the film. A 5 nm thin barrier layer was introduced between FePt and RuAl to prevent the inter-diffusion between RuAl and FePt. The influence of different barrier layers was studied. With a thin Ag sacrificial layer inserted between the barrier layer and the FePt magnetic layer, a smaller grain size can be achieved, the ordering temperature was lowered, and the (001) texture of FePt was enhanced. [ABSTRACT FROM AUTHOR]

We have experimentally investigated the effects of the interlayer thickness on recording performance, which was measured under various head clearances during writing and reading. In all cases, overwrite and write width always increase as the interlayer thickness is reduced. The signal-to-noise ratio, however, has a more complex dependence on the interlayer thickness: when the interlayer thickness is reduced, SNR is improved if head clearance during writing is large but is degraded if the head clearance during writing is small; SNR's dependence on the interlayer thickness becomes non-monotonic at intermediate head clearance during writing. Our data suggest that this complexity is caused by the interlayer thickness effects on the write field angle and gradient. [ABSTRACT FROM AUTHOR]

Micromagnetic simulation results on Co-based recording media are presented which examine the impact of a modified near-neighbor exchange interaction between grains of the form Jz (Miz Mjz ), reflecting the hexagonal crystal symmetry. Both out-of-plane and in-plane M-H loops are calculated, with an emphasis on a model fit to data reported by Wang et al. [IEEE Trans. Magn, vol. 43, p. 682 (2007)] on exchange coupled composite perpendicular media. The principle effect of Jz is to increase the coercivity and slope of both hard and soft layers. Improved agreement with experimental data for the in-plane loops is achieved by assuming a substantial value for Jz. Possibilities for measurement of Jz through spin-wave excitations are discussed. Thermal fluctuation effects are also examined through simulations of the magnetization vs temperature. [ABSTRACT FROM AUTHOR]

Head and media designs for shingled recording are described, targeting areal recording densities of 2-3 Tbit/in2. The potential of the designs was evaluated using micromagnetic simulations. The possibility of achieving multiple Tbit/in2 is demonstrated using a continuous, perpendicular recording medium. The effects of write head skew, inter-granular exchange coupling and read head offset are discussed. [ABSTRACT FROM AUTHOR]

Medium noise characteristics and transition jitter in perpendicular magnetic recording are explored using micromagnetic simulation. A noise plateau for intermediate recording densities is observed for a recording layer of typical magnetization. The plateau is replaced by a normal linear dependence of noise on recording density for a low magnetization recording layer. We show analytically that a source of the plateau is similar to that producing the non-linear transition shift of signal. In particular, magnetostatic effects are predicted to produce positive correlation of jitter and thus negative correlation of noise at the densities associated with the plateau. [ABSTRACT FROM AUTHOR]

Head and media designs for shingled recording are described, targeting areal recording densities of 2-3 Tbit/in2. The potential of the designs was evaluated using micromagnetic simulations. The possibility of achieving multiple Tbit/in2 is demonstrated using a continuous, perpendicular recording medium. The effects of write head skew, inter-granular exchange coupling and read head offset are discussed. [ABSTRACT FROM AUTHOR]

The FePt:C films with different volume fractions of carbon were epitaxially grown on the CrRu(200) underlayer with Pt and MgO intermediate layers. The magnetic properties and microstructure of these FePt:C films were investigated. The FePt:C films grown on Pt intermediate layer consisted of a continuous layer of FePt, with overlying granular FePt grains. The FePt:C films grown on MgO intermediate layer consisted of a granular FePt:C layer with overlying granular grains. The formation of the overlying granular FePt grains was attributed to carbon diffusion to the surface, which resulted in the second nucleation of FePt. The different interface energy and surface energy of FePt on Pt and MgO intermediate layers caused the formation of initial continuous FePt layer on Pt intermediate layer and initial granular FePt layers on MgO intermediate layer. The out-of-plane coercivity measured at room temperature increased from 10.2 to 19 kOe when C concentrations increased from 0 to 15%. Further increasing the C contents to 20% and 25% caused the decrease of coercivity to 17.2 and 14.8 kOe, respectively. The coercivity of the exchange coupling assisted FePt:C perpendicular media was indeed substantially reduced. [ABSTRACT FROM AUTHOR]

Abstract: The introduction of the soft magnetic underlayer (SUL) in perpendicular recording technology is to further increase the recording areal density. However, problems such as growth of the uncontrollable recording layer and additional media noise contributed from the SUL could be resulted. In this work, a synthetic antiferromagnetically (SAF) coupled (002) oriented Fe65Co35 film as an SUL was developed for L10 ordered FePt based double-layered recording media. The crystallography of hetero-epitaxially grown double-layered media CrRu/(Ru/FeCo)2/Pt/FePt/Ru was demonstrated. The L10 ordered FePt based double-layered perpendicular recording media with SAF coupled FeCo films as the SUL were developed. [Copyright &y& Elsevier]

Granular-type [(Co90Cr10)85Pt15]89.8-[SiO2]10.2 films were prepared by using co-sputtering methods, with Ru as a seed layer. Influences of Ru thickness on the micro-structure and magnetic properties of the CoPtCr-SiO2 magnetic layer were investigated. It was found that the seed layer obviously effected the grain isolation, c-axis distribution and magnetic parameters. The Ru seed layer with a suitable thickness is very helpful for achievement of high anisotropy, proper coercivity and high squareness. The anisotropy energy of the magnetic layer can be as high as 5×106erg/cm3 or more, even with a thin Ru layer, promising good thermal stability. It was noted that the Ru layer markedly enhanced the isolation of CoPtCr grains, corresponding to the increase of coercivity and the decrease of loop slope. Moreover, it was also revealed that the addition of SiO2 to CoPtCr effectively isolated the CoPtCr grains without disturbing the epitaxial growth of CoPtCr grains on the Ru seed layer. [ABSTRACT FROM AUTHOR]

A complex transverse ac susceptibility (χT) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin-film recording media. The technique has been used to measure the dispersions in grain size and the anisotropy field of perpendicular magnetic recording media. Experiments have been designed to study the key factors contributing to the anisotropy field distribution (σHk) in perpendicular media. The correlation between anisotropy dispersion, stacking faults, and recording performance have also been studied. A good correlation between stacking faults and σHK has been established. Lower stacking faults result in smaller anisotropy distribution and better media signal-to-noise ratio. The main factors controlling stacking faults are studied. Theoretical studies of the effect of interactions on the χT are also presented. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we discuss two key aspects of magnetisation reversal in magnetic thin films with perpendicular anisotropy. Firstly, a study has been made of the additional field required to erase data written perpendicular to a thin film recording disk as the linear data density is increased. It has been found that an increase in data density from 40 to 360kfci results in an increase of 1.25kOe in the field required to erase the data. Secondly, the effect of varying the level of exchange coupling by co-sputtering CoCrPt samples with SiO2 has been studied using a characterisation technique that is independent of the self-demagnetising field. It has been found that the samples are fully exchange de-coupled when the film contains >9.8% SiO2 and the activation volume of reversal remains constant for higher levels of SiO2. [Copyright &y& Elsevier]

Abstract: A method based on strain-induced phase transformation was used to lower the ordering temperature of FePt films. The strain resulted from the lattice mismatch between the FePt film and the substrate or underlayer favored the ordering. The relationships between the lattice mismatch, the ordering of FePt film, and the corresponding magnetic anisotropic constant were investigated. A critical lattice mismatch near 6.33% was believed to be most suitable for improving the chemical ordering of the FePt films. CrX (X=Ru, Mo, W, Ti) alloys with (200) texture was used to control the easy axis and ordering temperature of FePt films on glass substrate. Large uniaxial anisotropy constant K u⩾1×107 erg/cm3, good magnetic squareness (∼1) and FePt(001) texture (rocking curve −5°) were obtained at the temperature T s⩾250°C when using CrRu underlayer. The diffusion from overlying layers of Ag and Cu and an inserted Ag pinning layer were effective in reducing the exchange decoupling and changing the magnetization reversal. The media noise was effectively reduced and the SNR was remarkably enhanced when a 2nm Ag was inserted. [Copyright &y& Elsevier]

Abstract: We study the switching behavior of a patterned cylinder array in terms of the Landau–Lifshitz–Gilbert equation, including the effect of applied magnetic field, shape anisotropy, crystalline anisotropy, and dipolar interaction between particles. The condition of uncorrelated switching is obtained when the strength of dipolar coupling varies. It shows that a high anisotropy is needed to overcome the strong dipolar interaction in order to ensure the uncorrelated switching. Under the condition of uncorrelated switching, the switching of a single magnetic moment is still much different from the switching of an isolated magnetic moment (without dipolar interaction). The distributions of the critical switching field and switching time of a single magnetic moment for the different configurations of magnetic moments are obtained. By applying a transverse bias field, both the large critical switching field and the switching time can be effectively reduced. [Copyright &y& Elsevier]

The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (tSUL) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (∼80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (∼50 mn) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for tSUL < 100 nm. Comparable performance is achieved relative to media with tSUL 150 nm. [ABSTRACT FROM AUTHOR]

Abstract: A systematic investigation of the structural, magnetic, and recording properties of CoPtCrO media with different intergranular exchange coupling and anisotropy orientation dispersion is performed. Reduced exchange coupling between grains results in lower media transition jitter and nonlinear transition shift. By narrowing the Co anisotropy orientation dispersion, a substantial reduction of both transition and DC noise is achieved. Media with high squareness, coercivity, nucleation field, low exchange and narrow Co c-axis dispersion have been fabricated. Such media exhibit excellent recording performance and are promising for high-density perpendicular recording. [Copyright &y& Elsevier]

Abstract: The dependence of magnetic properties on thermal fluctuation and relationship between magnetic cluster size and thermal decay are investigated. It is shown that the use of the thermal stability factor explains the thermal decay of a perpendicular magnetic recording medium well when the magnetic cluster volume in AC erased magnetization is regarded as the effective volume. [Copyright &y& Elsevier]

Angle dependent magnetic hysteresis measurements in conjunction with micromagnetic simulations are used to determine the magnetic easy axis dispersion (ΔθEA) in perpendicular magnetic recording media. ΔθEA is found to be narrower than the crystalline c-axis dispersion, as measured using X-ray diffraction rocking curves. ΔθEA is further found to be reduced with increasing intergranular exchange coupling using a series of perpendicular CoCrPt alloy media. [Copyright &y& Elsevier]

By analyzing the magnetic cluster size of various media, we have investigated the variation of inter-granular exchange coupling with grain size. With the reduction of the grain size below 8.0 nm, higher inter-granular exchange coupled media showed a large increase in magnetic cluster size, while lower exchange media did not show as dramatic a cluster size change. This cluster size “knee” position was consistent with reduction in signal-to-noise ratio. To utilize small grain media for high density recording, it is desirable to push this “knee” position toward smaller grain size. [ABSTRACT FROM AUTHOR]

In this study we quantitatively determined the exchange coupling across B, C, SiOx, Cr and TaOx segregants by measuring the exchange coupling between two FePt layers separated by segregant layers of varying thickness. Our study indicates that the segregant that provides the best exchange break is TaOx; whereas, C is the worst and SiOx, Cr and B are in between. Our data indicates that a segregant intergranular region thicker than 0.8 nm should decouple FePt grains if B, TaOx, SiOx, or Cr are used, but with C, a thickness greater than 1 nm is required. [ABSTRACT FROM PUBLISHER]

We fabricated perpendicular media with decoupled magnetic grains that consist of a low magnetocrystalline anisotropy layer with various thicknesses directly grown on top of a high anisotropy layer. Nonuniform magnetization rotation was confirmed by measuring coercivity and remanent coercivity in these media. The reduction of remanent coercivity with increasing the low anisotropy layer thickness, measured at low temperature, is consistent with micromagnetic calculations. These results suggest domain wall assisted switching in composite media. [ABSTRACT FROM AUTHOR]

Magnetic recording in perpendicular media using write heads with trailing shields was simulated. The recording performance of discrete track media and continuous media was compared. Trailing shields increase the head field gradient, leading to sharper transitions and higher signal-to-noise ratio (SNR). The optimum trailing shield gap was determined to be 30 nm for both types of media. Using such a write head and subject to the condition of no adjacent track erasure the discrete track media SNR was 1.5 dB higher than the continuous media at a linear density of 1700 kfci. [ABSTRACT FROM AUTHOR]

Nano-granular L10 FePt:C composite films with perpendicular anisotropy were in situ deposited on glass substrates at 350 °C by dc magnetron sputtering. The magnetic, microstructural, and recording properties of the FePt:C perpendicular media were investigated. A good FePt (001) texture was maintained after incorporating up to 20 vol. % C, the measured full-width at half-maximum (FWHM) of the rocking curves of the FePt (001) peak slightly increased from 7.2° to 8.5°. FePt:C (20 vol. % C) films consisted of a continuous layer of FePt, with overlying granular FePt grains (5.6 nm) that were well separated by carbon. Hc increased from about 2600 to 3700 Oe with increasing C concentration from 0 to 15 vol.%, and then decreased with further increasing C concentration. The exchange coupling did not show obvious change with increased carbon content up to 20 vol. % due to the strong coupling between continuous layer and overlying granular FePt grains, which resulted in the overlap and fluctuation of recorded signals at a linear density of 221 kfci. [ABSTRACT FROM AUTHOR]

L10 FePt films with high perpendicular coercivity were successfully fabricated by using Cr65Mo15Mn20 underlayers with subsequent forming gas (Ar 95% + H2 5%) annealing. To adjust the strain energy and the orientation of FePt, Fe and Pt intermediate layers were used. Samples annealed at 275° C with thin Pt layers (<5 nm) show relatively small coercivity due to the stabilizing effects from the underlayers. With the increasing thickness of Pt, the strain was locally released and the (111) grains appeared. The nucleation of the ordered L10 FePt phase accompanied the formation of the FePt (111) phase, resulting in a high coercivity but deteriorated perpendicular anisotropy. To maintain the (001) preferred orientation with high coercivity, the sample with a 3.5-nm Pt layer was annealed at 350° C. The coercivity as high as 8400 Oe was realized. [ABSTRACT FROM AUTHOR]

Simulations of experiments to determine the fluctuation field and activation volume in perpendicular media show that the measurement is sensitive to the average grain size and the degree of easy axis distribution in the media, but is largely insensitive to the grain-size distribution, except when the medium is near saturation. Although the fluctuation field varies with the medium magnetization, there is generally no correlation between the size of the grains reversing and the activation volume as measured using the standard technique. [ABSTRACT FROM AUTHOR]

Write heads with rectangular and crescent-shaped main poles were used for simulations of recording in perpendicular media. Transition curvature was reduced by using a crescent-shaped head, but the lower head-field gradient also reduced the signal-to-noise ratio (SNR). The addition of a trailing shield narrowed the difference in SNR between the two types of heads, whilst the track width was up to 3 nm narrower when written by a crescent-shaped head. [ABSTRACT FROM AUTHOR]

The effect of second-order uniaxial anisotropy energy K2 on thermal stability and writability of perpendicular media has been studied. Due to the high orientation of crystalline easy axes, both energy barrier and dynamic coercivity of perpendicular media increases with K2. With relatively more increase in energy barrier, improvement of the tradeoff between thermal stability and writability can be achieved by Increasing K2. The field angle dependence with nonzero K2 is also quantitatively investigated. [ABSTRACT FROM AUTHOR]

In this paper we describe measurements of magnetic viscosity or time dependence in magnetic thin films suitable for use as perpendicular recording media. Generally, such effects cannot be measured using conventional magnetometry techniques due to the presence of a thin (0.1 μm) soft underlayer (SUL) in the media necessary to focus the head field. To achieve our results we have developed an ultrastable MOKE magnetometer, the construction of which is described. This has enabled us to measure nominally identical films with and without the presence of the SUL. We find that the presence of the SUL narrows the energy barrier distribution in the perpendicular film increasing the nucleation field (He), reducing the coercivity (Hc) and results in an increase in the squareness of the loop. This in turn results in an increase in the magnitude of the viscosity in the region of the Hc but that the range of fields over which the viscosity occurs is reduced. [ABSTRACT FROM AUTHOR]

Inverted hysteresis loops in a sputtered FeCo/Ru/FeCo bilayer have been investigated. A Stoner-Wohlfarth energy minimization calculation reproduced the negative remanence assuming a small misalignment of the easy axes of the ferromagnets. During the initial stage of the growth of the top layer, the external field fails to overcome the strong antiferromagnetic exchange coupling between the layers. The magnetizations, as a result, are no longer collinear and the easy axis of the top layer will vary with its thickness. The negative remanence disappeared following an annealing of the sample in a strong field confirming the theory. [ABSTRACT FROM AUTHOR]