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The switching fields and thermal stability of CoPt/Ru dot arrays with various dot thickness [delta] (5-20 nm) were experimentally investigated as a function of the dot diameter, D, (130-300 nm). All dot arrays showed a single domain state, even after removal of an applied field equal to the remanence coercivity [H.sub.r]. The angular dependence of [H.sub.r] for the dot arrays indicated coherent rotation of the magnetization during nucleation. We estimated the values of the 'intrinsic' remanence coercivity Ho obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation [E.sub.o]/([k.sub.B] T). The variation in [H.sub.o] as a function of [delta] and D was qualitatively in good agreement with that of the effective anisotropy field at the dot center [H.sup.eff.sub.k] (r = 0), calculated taking account of the demagnetizing field in the dots. The ratio of [H.sub.o] to [H.sup.eff.sub.k] (r = 0) for the dot arrays with [delta] = 10 nm increased from 0.53 to 0.70 as D decreased from 300 to 140 nm, and no significant difference in the [H.sub.o] to [H.sup.eff.sub.k] (r = 0) ratio due to the difference in 6 was observed. On the other hand, [E.sub.o]/([k.sub.B] T) decreased as [delta] decreased. [E.sub.o]/([k.sub.B] T) increased slightly as D decreased, but, was not so sensitive to D over the present D range. Index Terms--CoPt perpendicular films, dot arrays, remanence coercivity, single domain, thermal stability, patterned media.

The switching field distributions (SFD) of CoPtCr-Si[O.sub.2] perpendicular media as a function of Pt content were characterized by subtracting the effect of thermal agitation, and discussed in relation to the microstructure. DC demagnetizing (DCD) magnetization curves and minor dc demagnetizing (M-DCD) magnetization curves were measured at applied field sweep rates of ~10 Oe/s and ~[10.sup.8] Oe/s. We estimated the width of SFD, [DELTA] SFD, from the difference between the DCD and M-DCD curves, and defined them as [DELTA] [H.sub.r]/[H.sub.r] (at 10 Oe/s) and [DELTA] [H.sup.P.sub.r]/[DELTA] [H.sup.P.sub.r] (at ~108 Oe/s). The values of [DELTA] SFD characterized by subtracting the effect of thermal agitation, [DELTA] [H.sub.o]/[H.sub.o], were nearly half those of [DELTA][H.sub.r]/[H.sub.r] for 10-nm-thick media. [DELTA][H.sub.o]/[H.sub.o] was about 0.10 at 10 at % Pt content, and increased as the Pt content increased, reaching 0.17 at 30 at % Pt content. The increase in [DELTA][H.sub.o]/Ho was probably caused by an increase in the stacking fault density and the formation of fcc layers in the hcp CoPtCr lattice. A simple calculation based on the coherent switching of magnetization revealed that the c-axis distribution results in [DELTA][H.sub.o]/[H.sub.o] of about 0.08, independent of Pt content. These results suggest that the [DELTA] SFD due to the grain-to-grain anisotropy field variation was small, only 0.02-0.03. Index Terms--CoPtCr-Si[O.sub.2] perpendicular recording media, film composition, pulse field, switching field distribution, thermal agitation of magnetization.

The magnetic properties of dot arrays made of CoPt/Ru perpendicular films (20 nm thickness) were examined as a function of Pt content. The CoPt dot arrays with a dot size D of 140 nm showed a single domain state, after removal of the applied field equal to [H.sub.r]. [H.sub.r] decreased from 5.2 kOe to 3.0 kOe as the Pt content decreased from 20 at% to 14 at%. The angular dependence of [H.sub.r] for these dot arrays indicated coherent rotation of the magnetization during nucleation. The effective magnetic anisotropy, including the demagnetizing energy due to the dot shape, [K.sup.eff.sub.u], decreased as the Pt content decreased, resulting in the [H.sub.r] reduction. The values of the switching volume for nucleation, [V.sub.sw], evaluated from the stabilizing energy barrier [E.sub.0], were a few percent of the dot volume. The switching diameter for nucleation, [D.sub.sw], increased slightly as the Pt content decreased, which was qualitatively in good agreement with the increase in the exchange length of magnetization. The value of [E.sub.0]/[k.sub.B]T ([k.sub.B] is the Boltzmann constant and T is the absolute temperature) reduced as the Pt content decreased; however, [E.sub.0]/[k.sub.B]T still had a high of 440 even at 14 at% Pt content. We successfully demonstrated the reduction of [H.sub.r] for CoPt/Ru patterned films on reducing the Pt content, while simultaneously maintaining a high thermal stability. A calculation based on the experimental results suggested the potential recording density of CoPt/Ru dot arrays used for patterned media to be over 1 Tb/[in.sup.2]. Index Terms--CoPt/Ru perpendicular films, dot arrays, patterned media, remanence coercivity, single domain, thermal stability.

The effect of thermal agitations on the switching field distribution (SFD) of CoPtCr-Si[O.sub.2] perpendicular media was investigated, and the 'intrinsic' SFD caused by variations in the grain-to-grain switching field was determined. DC demagnetizing (DCD) magnetization curves and minor DCD (M-DCD) magnetization curves were measured at applied field-sweep rates of ~ 10 Oe/s and ~ [10.sup.8] Oe/s. We estimated the SFD from the difference between the DCD and M-DCD curves, and defined them as [DELTA][H.sub.r]/[H.sub.r] (at ~ 10 Oe/s) and [DELTA] [H.sup.P.sub.r]/[H.sup.P.sub.r] (at ~ [10.sup.8] Oe/s). The values of [DELTA] [H.sub.r]/[H.sub.r] were much larger than those of [DELTA] [H.sup.P.sub.r]/[H.sup.Psub.r]. Moreover [DELTA] [H.sub.r]/[H.sub.r] increased faster than [DELTA] [H.sup.P.sub.r]/[H.sup.P.sub.r] as the thickness decreased, suggesting that the SFD measured at vibrating sample magnetometer (VSM) time scales is significantly influenced by thermal agitation. The intrinsic SFD estimated using a series of media with various film thicknesses was about 0.14, which was 55%-75% of [DELTA] [H.sub.r]/[H.sub.r] for 8-16-nm-thick media. An analysis of the temperature dependence of [DELTA] [H.sub.r]/[H.sub.r] supported this conclusion. It is concluded that the SFD measured at VSM time scales is significantly influenced by thermal agitation of the magnetization, and the intrinsic SFD is likely to be nearly half that measured at VSM time scales. Index Terms--Film thickness, perpendicular recording media, pulse field, switching field distribution (SFD), temperature, thermal agitation of magnetization.

Dot arrays with diameter ranging from 80 to 245 nm are made of [Co.sub.80] [Pt.sub.20] films with large perpendicular anisotropy. Magnetic properties are investigated by detecting the anomalous Hall effect. The all arrays show angular dependence of remanent coercivity similar to coherent rotation. The result shows that reversal process is independent of dot diameter. The energy barrier height of magnetization reversal is estimated as 1.0 x [10.sup.-10] erg for the array consists of 140-nm-diameter dots. From the energy value, the switching volume is estimated as equivalent to the volume of a physical grain in the film. The results indicate that the reversal process starts from a nucleation of a 'reversed grain' followed by propagation process. Index Terms--Magnetic dot array, magnetic hysteresis, magnetization reversal.

The first and second order energy terms of uniaxial magnetic anisotropy, [K.sub.u1] and [K.sub.u2], of CoPtCr-Si[O.sub.2] perpendicular recording media were studied as a function of film composition and film structure. Moreover, the fabrication of CoPtCr-Si[O.sub.2] media having adequate values of [K.sub.u1] and [K.sub.u2] for high recording density was preliminarily studied. An analysis of CoPtCr films with various kinds of seed layer materials revealed that the values of [K.sub.u1] and [K.sub.u2] varied significantly with the seed layer material used, probably due to epitaxial growth of CoPtCr on the seed layers. [K.sub.u2] increased, accompanied by a reduction in [K.sub.u1] as the c/a ratio of the hcp-CoPtCr lattice increased. Moreover, experimental results suggest that a high stacking-fault density enhances the [K.sub.u2] values, especially in the high Pt content region. The addition of Si[O.sub.2] reduces the total anisotropy, [K.sub.u1] + [K.sub.u2], but no significant change in the ratio of [K.sub.u2]/[K.sub.u1] was observed. The fabrication of CoPtCr-Si[O.sub.2] media with adequate values of [K.sub.u1] and [K.sub.u2] was successfully demonstrated, although more intensive efforts to enhance grain isolation are required to confirm the advantages conferred by the [K.sub.u2] term. Index Terms--CoPtCr-Si[O.sub.2] high order energy term, lattice deformation, magnetic anisotropy, perpendicular recording media, thermal stability.

Magnetic properties of dot arrays of [L1.sub.1] type Co-Pt ordered alloy perpendicular films are analyzed. The switching field distribution is relatively small, even for dot arrays prepared on glass disks, showing the homogeneous formation of a [L1.sub.1] type ordered structure in the [Co.sub.50][Pt.sub.50] layers.

Magnetic properties of hard/soft stacked dot arrays consisting of thin Co/Pt superlattice hard layers and Co soft layers are examined as functions of Co soft layer thickness and the interfacial exchange coupling between the hard and soft layers. Pt is used as the control layer of the interfacial exchange coupling and Co soft layers are sandwiched with Pt layers to induce surface anisotropy on the Co soft layers.

The magnetic properties of [Co.sub.80][Pt.sub.20]/Co hard/soft stacked dot arrays with dot diameters D of about 50 nm are analyzed. The studies have confirmed that the hard/soft stacked structure reduced the angular variation of the remanence coercivity.

The effect of thermal agitation on the switching field distribution (SFD) of CoPtCr-Si[O.sub.2] perpendicular media is investigated. It is concluded that the SFD measured at vibrating-sample magnetometer (VSM) time scales is significantly influenced by thermal agitation of the magnetization, and reduction of the grain size distribution is the most effective way to reduce the SFD at VSM time scales.

Measurements of higher energy term of magnetic anisotropy, Ku2, in CoPtCr-SiO2 perpendicular recording media are described. It is concluded that CoPtCr films have suffecient potential in the values of Ku1 and Ku2 for high-density perpendicular media.

Magnetic properties of dot arrays of L11 type Co–Pt ordered alloy perpendicular films were studied. L11-Co–Pt films with a large uniaxial magnetic anisotropy Ku of the order of 107 erg/cm3 were fabricated at a substrate temperature of 360 °C using ultrahigh vacuum sputter film deposition. Dot patterns with dot diameters of 70–200 nm were made using high resolution e-beam lithography and reactive ion etching (RIE). The values of Ku were measured by the GST method using the Anomalous Hall Effect; we observed the averaged signals of 6000 dots. The values of Ku for dot arrays of 10-nm-thick L11-Co50Pt50 films deposited on MgO(111) substrates (single crystal films) and glass disks (polycrystalline films) were nearly the same as those of the original films independent of D, indicating no significant etching damage by the RIE process. Magnetic force microscopy images revealed that all dots were single domains in the present D region. The coercivity Hc of the dot arrays was 25.0 kOe [MgO(111) substrate, D=70 nm] and 14.3 kOe (glass disks, D=80 nm). The switching field distribution σ/Hc was relatively small, σ/Hc=0.15, even for dot arrays fabricated on glass disks, indicating the homogeneous formation of a L11 type ordered structure in the Co50Pt50 layers. [ABSTRACT FROM AUTHOR]

The effect of thermal agitations on the switching field distribution (SFD) of CoPtCr–SiO2 perpendicular media was investigated. Dc demagnetizing (DCD) magnetization curves and minor dc demagnetizing (M-DCD) magnetization curves were measured at applied field sweep rates of ∼10 and ∼108 Oe/s. We estimated the SFD from the difference between the DCD and M-DCD curves, and defined them as ΔHr/Hr (at ∼10 Oe/s) and ΔHrP/HrP (at ∼108 Oe/s). The values of ΔHrP/HrP were found to be 60%–70% of ΔHr/Hr. The difference between ΔHrP/HrP and ΔHr/Hr should be caused by thermal agitation of the magnetization. The influence of the distribution of the thermal agitation on SFD was calculated using the distribution of the grain volumes. It is concluded that the SFD measured at vibrating-sample magnetometer (VSM) time scales is significantly influenced by thermal agitation of the magnetization, and reduction of the grain size distribution is the most effective way to reduce the SFD at VSM time scales. [ABSTRACT FROM AUTHOR]

Measurements of higher energy term of magnetic anisotropy, Ku2, in CoPtCr-SiO2 perpendicular recording media are described. It was revealed that the values of Ku2 and the first order energy term, Ku1, vary significantly according to the seed layer material used, however, no significant change in the ratio of Ku2/Ku1 was observed on the addition of SiO2 to CoPtCr films. Ku2 increases and Ku1 decreases as the c/a ratio of the hcp-CoPtCr lattice increases. It is concluded that CoPtCr films have sufficient potential in the values of Ku1 and Ku2 for high density perpendicular media. [ABSTRACT FROM AUTHOR]