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The high-frequency characteristics of the RF integrated inductors with antiferromagnetic/ferromagnetic (AF/F) multilayers (MLs) are studied. Each AF layer is 8-nm IrMn and F is [Co.sub.50] [Fe.sub.50] with a 200-nm splitting into N = 1 to 5 repeats of MLs. This exchange coupled {IrMn/CoFe(d nm)}[sub.N] MLs are deposited on top of the two-port inductors with five-turn square spiral coils, a dimension of 100 [micro]m x 100 [micro]m and line/space of 5 [micro]m/2 [micro]m. The inductor surface and magnetic layer is separated by 1-[micro]m-thick Si[O.sub.2]. The enhancement of inductance ([DELTA]L) is 20% compared to an air-core of the same coil size. The resonance peak gradually shifted to a higher frequency with increasing N, and reached at a maximum of 4.3 GHz when N = 5. This is in good agreement with our magnetic data which revealed that the anisotropy field ([H.sub.k]) and ferromagnetic resonance frequency ([f.sub.FMR]) of {IrMn/CoFe(d nm)} [sub.N] MLs are increased with increasing N. The quality factor, Q is improved by 6.8% at 1.5 GHz for the {IrMn/CoFe(40 nm)}[sub.N=5] integrated inductors compared to air-core inductors. Index Terms--Antiferromagnefic (AF), exchange coupling, ferromagnetic resonance (FMR), frequency response, radio-frequency (RF) inductor.

A simple approach is proposed for fabrication of percolated perpendicular media (PPM). Nano pore array with pore diameter of 12-15 nm and different pore densities has been prepared by anodizing aluminum on silicon wafers. The pore density increases from 3.2 x [10.sup.10] [cm.sup.-2] to 11.0 x [10.sup.10] [cm.sup.-2] with the decrease in anodizing voltage from 30 to 10 V. Then, Pt (7 nm)/{Co (0.5 nm)/Pt (2) nm}5 multilayers are deposited onto this porous anodized alumina (AAO) by sputtering. The pore size is reduced to 10-12 nm after deposition of magnetic layers. The Co/Pt multilayers on AAO exhibit perpendicular magnetic anisotropy, squarness ratios of unity, and negative nucleation fields. The perpendicular coercivity increases linearly with the increase in pore density due to the pinning effect imposed by the pores, which is consistent with theoretical calculation for PPM. Index Terms--Anodized aluminum oxide (AAO), Co/Pt multilayers, percolated perpendicular media (PPM), pinning sites.

Twenty-nanometer FePt films with 40% Fe content were deposited on MgO substrates at 300[degrees]C. A perfect (001) preferred orientation of FePt L[1.sub.0] phase was obtained. After 700[degrees]C annealing in vacuum, a room temperature perpendicular anisotropy of as high as 4.5 x [10.sup.7] erg/[cm.sup.3] can be obtained. The Curie temperature of the sample with 40% Fe content is far below the 50% Fe sample, which can effectively reduce the temperature of the thermal writing process. Furthermore, decay of magnetic anisotropy energy ([K.sub.u]) is much faster than saturated magnetization ([M.sub.s]) with rising temperature, which results in a domination of demagnetization (DM) energy at high temperature. Therefore, a further reduction of the switching field can be achieved. Finally, the films show almost the same magnetic properties during 10 times thermal writing processes from 25[degrees]C to 300[degrees]C, implying this media has high reliability for thermal writing process. Index Terms--Demagnetization, FePt with 40% Fe content, MgO substrate, perpendicular anisotropy, thermal writing.

PtMn nanoparticles have been synthesized by chemical methods. The as-synthesized PtMn nanoparticles show superparamagnetic behavior at room temperature and ferromagnetic behavior at 5 K due to the uncompensated surface spins originating from the finite size effect. Different PtMn sizes were obtained after various temperature annealing processes. The exchange bias and vertical loop shift of PtMn nanoparticles were observed at 5 K in field cooling process and were ascribed to the exchange coupling of ferromagnetic surface spins and the antiferromagnetic core. It was found that the coercivity and exchange bias field were strongly related to the particle size. Index Terms--Exchange bias, PtMn nanoparticles, size dependent, vertical loop shift.

High-quality epitaxial Zn[Co.sub.0.07]O films deposited at room temperature were obtained by using reactive ion beam sputtering. Room-temperature ferromagnetic behavior of ZnCoO was observed with a coercivity of 70 Oe. We observed the loop shift at 5 K in the field-cooled samples of ZnCoO/Cu/IrMn and an enhanced coercivity in the zero-field-cooled samples, which indicated the existence of exchange coupling between ZnCoO and IrMn through a thin Cu layer (0.15 nm). Furthermore, the exchange field of ZnCoO was increased from 55 to 113 Oe by increasing the cooling field from 3 to 15 kOe. Index Terms--Dilute magnetic semiconductor (DMS), exchange bias, IrMn, ZnCoO.

(001) IrMn/CoFe epitaxial bilayers were fabricated on Si substrates at room temperature by using Cu underlayers. A double shifted loop was observed at the axis perpendicular to the exchange bias direction. The dependence of anisotropy on the IrMn thickness was studied. The magnetization reversal was investigated by using vector coil measurements and calculations based on Stoner-Wohlfarth model. A combination of reversible and irreversible rotation was observed for the magnetization reversal along the hard axis. Critical angles and fields at which irreversible rotation occurred were obtained through simulations. Index Terms--(001) IrMn/CoFe, double shifted loop, exchange bias, magnetization reversal.

We analyzed anisotropy in IrMn/CoFe/Fe[O.sub.X]/CoFe multilayers with angular remanence measurements. The results showed the coexistence of biquadratic and unidirectional anisotropies. A significantly asymmetric magnetization reversal had been observed. We studied the reversal mechanism by using vector coils and suggested that the switching in the decreasing branch comprised both coherent rotation and 90[degrees] domain wall motion; however, the switching in the increasing branch showed complicated multidomain rotation. Index Terms--Asymmetry, biquadratic anisotropy, exchange bias, Fe[O.sub.x], magnetization reversal, nano-oxide layer (NOL).

There exist two conductivities in the system with the spin Hall effect: the Drude conductivity and the anomalous Hall conductivity. Our theoretical results based on the effective mean-free-path model show that the asymmetry in these two conductivities induces a spin-dependent, directional diffusive scattering, and thus causes the spin accumulation. Index Terms--Spintronics, spin accumulation, spin Hall effect.

We studied the effects of the deposition Ar pressure on the switching field distribution (SFD) of Tb/Pt/Ru/CoPtCr-Si[O.sub.2] perpendicular media. In this study, we describe a simple method for obtaining parameters of the SFD such as the standard deviation (SD) while taking the effect of demagnetizing field into account. The SFD changed its character greatly with the change of Ar pressure. The differences in the SD of the SFD of various samples may originate from the variation of intergranular exchange and the demagnetizing field due to different Ar pressure. Index Terms--Demagnetizing field, perpendicular recording media, switching field distribution, switching volume.

Ag nanoparticles with [Fe.sub.3][O.sub.4] shells have been synthesized by the polyol method. The Ag@[Fe.sub.3][O.sub.4] core-shell nanoparticles exhibited a superparamagnetic behavior at the temperature higher than the blocking temperature (100 K) and showed shifted loops under a field cooling process. The enhanced magnetic anisotropy was observed and was ascribed to the surface effect. Index Terms--Core-shell structure, exchange bias, [Fe.sub.3][O.sub.4] nanoparticles, superparamagnetic.

L[1.sub.0] FePt films with high perpendicular coercivity were successfully fabricated by using [Cr.sub.65][Mo.sub.15][Mn.sub.20] underlayers with subsequent forming gas (At 95% + [H.sub.2] 5%) annealing. To adjust the strain energy and the orientation of FePt, Fe and Pt intermediate layers were used. Samples annealed at 275[degrees] C with thin Pt layers ( Index Terms--[Cr.sub.65]M[o.sub.15][Mn.sub.20], FePt, forming gas annealing, perpendicular media.

We observed the coexistence of biquadratic and unidirectional anisotropy in the CoFe layer by inserting the nano-oxide-layer Fe[O.sub.x] in the IrMn/CoFe bilayers. Analyses of X-ray magnetic circular dichroism suggested that the FeOx possessed ferromagnetic components. Mixed valence states of Fe, [Fe.sup.2+] and [Fe.sub.3+] were observed in the Fe[O.sub.x] layer, which implied that both antiferromagnetic and ferromagnetic components might co-exist in the Fe[O.sub.x] layer. The uniaxial anisotropy in CoFe at 90[degrees] may originate from the interaction of CoFe with the antiferromagnetic components of the Fe[O.sub.x] layer in the presence of interfacial magnetic roughness. The unidirectional anisotropy at 0[degrees] may result from the exchange biasing from the IrMn layer through the ferromagnetic components in the Fe[O.sub.x] layer. Index Terms--Biquadratic coupling, exchange biasing, Fe[O.sub.x], interlayer coupling, nano-oxide-layer.

A low temperature ordering of L[1.sub.0] FePt phase was directly achieved by using 2-MeV He-ion irradiation without conventional post-annealing. The coercivity greater than 5700 Oe can be obtained by using ion-irradiation heating at temperature as low as 230[degrees]C. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Index Terms--Beam heating, FePt, irradiation, ordering.

The effects of Co insertion at the interface of CoCrPtB-Ru-CoCrPtB AFC media are investigated. Although the exchange coupling constant J can be increased by inserting Co, undesired magnetic properties are observed including reduction of the switching field of the stabilizing layer or reduction of coercivity of the recording layer. We propose a new antiferromagnetically coupled structure with a laminated stabilizing layer composed of CoCrPtB-(Ru or CoCr)-Co, in which Co remains at the interface to enhance J and a nonmagnetic layer Ru or CoCr is used for suppressing interaction between Co and lower CoCrPtB layer. The coercivity of the laminated stabilizing layer decreased and the switching field increases with increasing thickness of Ru or CoCr. Consequently, the insertion of Ru or CoCr can make the magnetization reversal of the stabilizing layer easier. Index Terms--Antiferromagneticany coupled (AFC), CoCr, Ru, switching field.

Pseudo-antiferromagnetically coupled (AFC) structure media are fabricated by replacing the ferromagnetic layers adjacent to the Ru layer with nonferromagnetic layers in the AFC media. Lattice mismatching is manipulated by changing Ru to RuCo(Cr) alloys. The medium without Ru shows narrower PW50 and higher signal-to-noise ratio (SNR) than the pseudo-AFC medium with Ru. After replacing Ru with RuCo or RuCoCr, the PW50 and SNR are nearly constant when the thickness of Ru alloy is in the range of 0 to 8 [Angstrom]. X-ray data show that better Co (11.0) texture is found in the pseudo-AFC media with Ru alloy layer than Ru layer. Transmission electron microscope images indicate that the Ru layer enlarges the grain and broaden its distribution. Index Terms--AFC media, grain size, lattice matching, pseudo-AFC structure, PW50, signal to noise.

The addition of 2 % Zr into the CrMo underlayer reduced the grain size of the recording layer to 5.33 nm and achieved a narrow distribution of grain size. The addition of 5% Mn into the CrMo underlayer enhanced the crystallographic texture and coercivity. To obtain both advantages of Zr and Mn doping effects, the Zr and Mn doped double underlayer were introduced in longitudinal media. The magnetic properties and microstructures of the recording layers on CrMoMn-CrMoZr and CrMoZr--CrMoMn double underlayers mainly depended on the underlayer adjacent to the CoCr layer, whereas the underlayer on NiP further modified the characteristics of the recording layers. By combining the CrMoMn and CrMoZr double underlayers, longitudinal media revealed enhanced coercivity, small intergranular coupling, and a narrow distribution of grain size. Index Terms--CrMoMn underlayer, CrMoZr underlayer, double underlayer, grain size, intergranular coupling, longitudinal media.

The effects were investigated of carbon ion dose on the exchange field and GMR ratio of irradiated PtMn-based spin valves. The exchange field increases with increasing dose in the low ion-dose-regime, which is attributed to the increase in PtMn(C) formation. The maximum enhancement of the exchange field can be as large as 50% for the ion dose of 2.0 x [10.sup.14] ions/[cm.sup.2]. The reduction of the exchange field in the high-dose regime is probably due to the intermixing or carbon residue at the interface. The giant magnetoresistance (GMR) ratio monotonically decreases with increasing carbon dose. Ion irradiation shows different effects on fcc and fct PtMn samples. By proper annealing prior to irradiation, we can obtain a large enhanced exchange field and a reasonably good MR ratio. Index Terms--Exchange field, giant magnetoresistance (GMR), ion irradiation, PtMn-based spin valves.

We have studied the temperature effect on magnetic properties in (001) epitaxial Co-NiMn. The interfacial exchange coupling in Co-NiMn not only induces a unidirectional anisotropy but also a uniaxial anisotropy. Double shifted hysteresis loops could be found along the hard axis, and used to accurately determine the anisotropy constants using the coherent rotation model. The cubic anisotropy of Co decreases monotonically with increasing temperature, while the interface-induced uniaxial anisotropy decreases with increasing temperature up to 180[degrees]C, and then increases with further increasing temperature. A mechanism explaining the enhancement of interface-induced uniaxial anisotropy and coercivity at temperatures above 180[degrees]C is proposed. Index Terms--Anisotropies, coercivity, double shifted hysteresis loop, induced uniaxial anisotropy, thin film, vibrating sample magnetometer, (001) epitaxial Co-NiMn.

We have investigated the effect of microstructure and interface conditions on the anisotropic exchange fields of NiO/NiFe bilayers. The NiO films were deposited by dc magnetron reactive sputtering. By using different substrates or annealing NiO films, grain size and surface roughness of NiO can be manipulated. The exchange field is enhanced in the small-grained NiO and this enhancement is attributed to the formation of small domains in NiO. The degree of interfacial roughness and the existence of (111) texture showed no correlation with exchange field.

High magnetization (Mr) and enhanced coercivity magneto-optical (MO) recording media TbFeCo (TFC) were investigated for hybrid magnetic flux reading/optical recording due to their large magnetic flux. To increase the stability of high Mr TFC media, dual-layer disks composed of TM-rich readout layer with saturation magnetization (Ms) = 370 emu/[cm.sup.2] and RE-rich memory layer were fabricated. Coercivity and interface energy between double layers as a function of active layer thickness were examined. By simulating thermo-magnetic writing, the dual-layer media were shown to be applicable for optical writing/magnetic flux reading recording. Index Terms--Coercivity, hybrid magnetic flux reading/optical recording, magnetic flux, magnetization.

Textured and epitaxial {001} NiFe/NiMn/Co films were grown on Cu/Si (100) structural templates by using e-beam evaporation. Numerical analysis of high-resolution TEM images was used to determine the local d-spacing of NiMn. The local c/a ratio for the annealed sample varied across the film. The well-aligned orientation relationship between NiFe and NiMn stabilized the disordered NiMn phase, which resulted in a small exchange field. Interdiffusion was observed by energy dispersive X-ray spectroscopy near the interfaces of Cu/NiFe, NiFe/NiMn, and NiMn/Co. Interdiffusion may modify the interfacial structures, and may contribute to the enhancement of the coercivity in NiFe and Co. Index Terms--{001} NiFe/NiMn/Co, exchange field, high-resolution TEM, interdiffusion.

The exchange field and domain configurations were investigated in patterned polycrystalline and (100) NiO/NiFe films. The exchange field was enhanced in the polycrystalline patterns with the aspect ratio larger than one (the long edge parallel to the original easy axis). Exchange field of patterned (100) NiO/NiFe on MgO, in contrast, showed little dependence on the aspect ratio, but strong dependence on the pattern size. The exchange field increased from 8.6 Oe in the sheet film to 48.4 Oe in the 2 μm patterns. The different dependence of the exchange field of polycrystalline and (100) NiO/NiFe on the pattern size can be plausibly explained by the difference of the domain size in NiO, and the variation of the blocking temperature distribution. Magnetic force microscopy images of patterned polycrystalline NiO/NiFe showed two kinds of domain configurations (single-domain state and multidomain state) in the sample with the pattern size of 2 μm, which may be the direc! t observation of various exchange paths at the interface of NiO/NiFe. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]