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Highly ordered (001)-oriented FePt nanoparticles (NPs) with controllable sizes and well-aligned easy axis were obtained by tuning the total layer number n of atomic-scale [Fe/Pt/SiO2]n multilayers deposited on SiO2∥Si substrates. After annealing at 700 °C, the ordered FePt NPs with a small particle size of 5.5 nm (an extremely high areal density of 1.2×1013dots/in.2), a large out-of-plane coercivity of 28.5 kOe, and a narrow size distribution of 13% were attained. All NPs were embedded in the SiO2 substrates, resulting in a flat top surface. Finally, a full-stack film structure of perpendicular recording media composed of FePt NPs (recording layer), SiO2 (nonmagnetic intermediate layer) and CoZrTa (soft underlayer) was demonstrated. [ABSTRACT FROM AUTHOR]

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO2 dot arrays formed on a Si wafer. At first, arrays of the SiO2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO2 dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO2 dots are about 24, 43, and 17 nm, respectively. Then {Co(0.4 nm)/Pt(0.08 nm)}8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO2 dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO2 substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner–Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array. [ABSTRACT FROM AUTHOR]

A simple nanofabrication process is introduced to tune the exchange bias in the magnetic nanostructures with a feature size below 15 nm. The IrMn/CoFe films are deposited on the porous alumina oxide (AAO) with different pore diameters from 10 to 48 nm, keeping the center-to-center distance almost the same at 60 nm, which is fabricated on Si wafers. A large enhancement in the exchange field Hex (2.3 times) and the coercivity Hc (8 times) is observed in the nanostructure compared to the continuous film. The exchange field is decreased with increasing pore diameter; on the other hand Hc increases continuously with increase in pore diameter. However, the values of Hex and Hc for all the exchange bias nanostructures are larger than those of the continuous film. These effects are mainly ascribed to the creation of domain walls or domains due to the pinning effect and the physical limitations that the pore size and edge-to-edge distance impose on both ferromagnetic and antiferromagnetic layers. Our results strongly support that exchange bias can be tuned by the AAO pores. [ABSTRACT FROM AUTHOR]

The laminated soft layer (LSL) that comprises the granular [CoPtCr–SiO2/Pt]N multilayers with perpendicular magnetization is designed to reduce the switching field of exchange coupled composite (ECC) media. The magnetic simulation shows that the reduction in the switching field can be optimized by changing the coupling strength between the adjacent CoPtCr–SiO2 layers in LSL. The reversal mechanism of ECC media with LSL depends on the bilayers number N of [CoPtCr–SiO2/Pt]N. Both simulation and experiments reveal that the domain-wall assisting reversal strongly depends on the thickness of LSL. By properly adjusting the coupling strength inside the LSL, the switching and saturation fields can be significantly reduced at a limited thickness of the soft layer due to decreased domain-wall length by the Pt lamination. [ABSTRACT FROM AUTHOR]

We investigated the reorientation of exchange anisotropy in the epitaxial (002) IrMn/CoFe bilayers. Transitions of exchange-bias field from a negative field to a positive field with increasing time scale were observed at room temperature. The negatively magnetized state combining with the strong magnetocrystalline anisotropy of CoFe may raise the probability that the interfacial spins of thin IrMn layers were thermally relaxed to the direction of CoFe magnetization; therefore, after a period of time, the exchange-bias direction was reversed. This process can be further enhanced when samples were placed under the setting field. The double-shifted magnetization curve observed in this system was used as a good indicator for the relaxation of interfacial spins of IrMn. [ABSTRACT FROM AUTHOR]

Highly ordered L10 FePt–SiO2 granular films with a (001)-preferred orientation were obtained by depositing atomic-scale [Fe/Pt/SiO2(tox)] multilayers on glass substrates and subsequently annealing multilayers at the temperature of as low as 350 °C. The tox value plays an important role on both microstructure and magnetic properties. The average grain sizes of samples A, B, and C (tox=0.11,0.28,0.56) are 12.12, 15.46, and 5.14 nm, respectively, and the corresponding perpendicular coercivities are 6800, 5550, and 7700 Oe. Due to different microstructures, samples show distinct coercivity dependence on annealing time. [ABSTRACT FROM AUTHOR]

The oscillatory perpendicular interlayer-coupling field and strength as a function of Ru spacer thickness were studied for samples of the [Co/Pt]5/Co/Ru/Co/TbCo structure. For Ru thickness in the range of 0.5–1 nm, a strong antiferromagnetic (AF) coupling (J∼0.38 erg/cm2) was observed. When AF coupling existed, the coercivity of Co/TbCo bilayers was enhanced because the Co/Pt multilayers stabilized the magnetization direction of Co/TbCo. Consequently, oscillatory coercivity of Co/TbCo with Ru thickness was also observed. Since the magnetization direction of the Co sublattice in TbCo can be tuned by adjusting composition or measuring temperature, the direction of the shifted minor loop of Co/Pt multilayers can be varied accordingly while keeping the same Ru thickness. [ABSTRACT FROM AUTHOR]

(0002) textured and epitaxial ZnCo0.07O films were fabricated at room temperature by ion beam deposition on Si substrates. Hall measurement revealed that ZnCo0.07O films were n-type semiconductors with carrier concentrations higher than 1019/cm3. The carrier concentration of ZnCo0.07O can be manipulated by controlling the oxygen flow rate during deposition or by postannealing. The saturation magnetization and magnetoresistance ratios strongly depended on the carrier concentration. In addition, epitaxial (0002) ZnCo0.07O films, grown on Cu underlayers, showed room-temperature ferromagnetism, which may be potentially used for spintronic devices. [ABSTRACT FROM AUTHOR]

CuZn antisite defects have been regarded as the efficiency limiting factor of kesterite solar cells because they cause band tailing and loss of open circuit voltage (VOC). To suppress CuZn antisite defects, Ag-alloyed (Ag,Cu)2ZnSn(S,Se)4 (ACZTSSe) kesterite has been proposed. Although efficiency enhancement is realized by a limited amount of Ag addition (Ag/(Ag + Cu) ≤ 20%), the antisite defects may not be completely eliminated by the small amount of Ag. Further enhancement by using a high Ag content (Ag/(Ag + Cu) ≥ 20%) has not been achieved yet. In this work, the effects of Ag on the phase stability, crystal structure, defect properties and device performance are investigated. Experimental results demonstrate that the optimized formation temperature of kesterite is reduced with increasing Ag content. We demonstrate that Ag2ZnSn(S,Se)4 is ordered kesterite and CuZn antisite defects are effectively eliminated as 35% of Cu is replaced by Ag in ACZTSSe. To further increase the efficiency of the high Ag-content kesterite, 1 at% Na addition to the precursor is critical to passivate the interface as well as grain boundaries and increase the carrier concentration. An efficiency of 10% for ACZTSSe solar cells is reported with Ag/(Ag + Cu) = 35% at a processing temperature as low as 470 °C through an environment-friendly chemical spray pyrolysis process using aqueous solution. This study demonstrates the feasibility of controlling antisite defects and band-gap engineering by a larger amount of Ag substitution in the kesterite system to solve the VOC deficit problem. [ABSTRACT FROM AUTHOR]

The exchange-bias films of ferrimagnetic/ferrimagnetic, ferromagnetic/ferromagnetic, and ferromagnetic/antiferromagnetic bilayers were fabricated to investigate their interfacial exchange energy Δσ. Δσ of TbFeCo bilayers is larger than 5 erg/cm[SUP2]at room temperature. By varying the composition of TbFeCo layers, both positive and negative exchange bias have been observed. A highly uncompensated-spin interface model was proposed to explain the strong exchange interaction in TbFeCo bilayers. Due to the characteristics of highly uncompensated-spin interface at TbFeCo bilayers, the exchange coupling field in TbFeCo bilayers exhibited less dependence on interfacial roughness than that in IrMn/NiFe bilayers. In addition, by adjusting the composition of TbFeCo, the anisotropy of pinning layer can be manipulated and exhibits strong effects on exchange bias of TbFeCo bilayers. [ABSTRACT FROM AUTHOR]

C-ion irradiation was performed in CoFe/PtMn and CoFe/IrMn systems with an applied field during irradiation to investigate the effects of the energy transfer between C ions and antiferromagnetic atoms (AF) on the exchange field H[SUBex]. The irradiated CoFe/PtMn samples showed reduced exchange fields and coercivity, which was attributed to the lattice distortion of PtMn. When samples were irradiated with an applied field antiparallel to the original exchange-bias direction, a partially reversed H[SUBex] was found in CoFe/PtMn, while a fully reversed H[SUBex] in CoFe/IrMn was observed at the dose of 2 ×10[SUP14] ions/cm[SUP2]. Rapid energy transfer and temperature increase, originating from the interaction between C ions and AF atoms, resulted in spin reversal and formation of reversed AF domains when samples were irradiated in antiparallel fields. In addition, the thermal relaxation of H[SUBex] in CoFe/IrMn was suppressed by ion irradiation. [ABSTRACT FROM AUTHOR]

FeTaCN films, prepared by using reactive sputtering, were studied for the application for soft underlayers of perpendicular media. As-deposited FeTaCN nanocrystalline films with a N[SUB2]/Ar ratio of 5% exhibited high saturation moment (B[SUBs] = 1.63 T) and low coercivity (1.4 Oe). IrMn/FeTaCN exchange-biased multilayer films and CoSm/FeTaCN hard-biased films were investigated to control the domain structure and magnetization reversal in FeTaCN films. Exchange bias field is inversely proportional to the thickness of FeTaCN films and reaches 11.4 Oe in the laminated sample of [IrMn (8 mm)/FeTaCN (50 nm)]×4. The interfacial coupling energy between IrMn and FeTaCN is 0.09 erg/cm[SUP2]. The biasing field of CoSm/FeTaCN can reach a maximum value of 10.6 Oe at the FeTaCN thickness of 200 nm. The corresponding interfacial coupling energy of FeTaCN/CoSm is as large as 0.27 erg/cm[SUP2]. [ABSTRACT FROM AUTHOR]

The alloy doping effects of the CrMo underlayer were investigated on the texture, grain size, and magnetic properties of CoCrPt longitudinal media. 5% Mn dissolving into CrMo lattices enhanced the texture of the recording layer and significantly raised the coercivity from 2200 (on the CrMo underlayer) to 3200 Oe. Further increases in the Mn content resulted in the grain growth of the recording layer, and less enhanced coercivity. The doped Zr, Ag, and Nb atoms into CrMo underlayers were segregated and led to reduction of grain size. Among them, Zr doping exhibited the most pronounced effects. [ABSTRACT FROM AUTHOR]

We have investigated the coupling between top and bottom pinned layers through various nano-oxide layers (NOLs) in IrMn-based spin valves. The NOLs were formed by using oxygen-plasma oxidation or natural oxidation on 1 nm metallic layers. By inserting naturally oxidized Co-NOLs in the pinned layer, strong ferromagnetic coupling through NOLs and high specularity at the NOL interface were achieved. In contrast, when the plasma-oxidized Co-NOLs were inserted, ferromagnetic coupling through NOLs disappeared, plausibly due to the formation of nonferromagnetic oxides, which led to a low magnetoresistance (MR). Insertion of naturally oxidized Ni[SUB80]Fe[SUB20]-NOLs showed the same results as that of naturally oxidized Co-NOLs. On the other hand, biquadratic coupling between top and bottom pinned-Co[SUB90]Fe[SUB10] layers was observed by inserting plasma-oxidized Ni[SUB80]Fe[SUB20]-NOLs. The highest MR was obtained when the field was applied along the direction perpendicular to the field-annealing direction. Similar biquadratic coupling was also found with naturally oxidized or plasma-oxidized Fe-NOLs. We suggest that the biquadratic coupling between pinned Co[SUB90]Fe[SUB10] layers through NOLs results from the coupling between Fe (or Co[SUB90]Fe[SUB10] and Fe[SUP+3] oxides. [ABSTRACT FROM AUTHOR]

From the linear response Boltzmann transport equation in the relaxation-time approximation, we investigate the structure consisting of magnet-metal-magnet multilayers inserted by the nano-oxide layer. Moreover, we propose a modified Boltzmann transport equation with the appropriate boundary conditions in multilayers instead of solving the complicated coupled equations. We find that the nano-oxide layer causes the decrement of the diffusive scattering effect and the increment of the reflective effect, and the magnetoresistance ratios vary with different positions of the nano-oxide layer. The theoretical results are reasonable in agreement with the experimental data. [ABSTRACT FROM AUTHOR]

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance (MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 °C. The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR. [ABSTRACT FROM AUTHOR]

Single-twin (T)-domain NiO films were obtained by stress induced during the growth, and the exchange anisotropy between NiO and NiFe films was studied by using micromagnetic modeling. The compressive strain along the [111] is -7.16 × 10[sup -4], which forces spins of NiO to lie on the (111) plane parallel to the film surface. The neutron diffraction shows that the moments of NiO predominantly lie in the film plane with random orientations, that is, the NiO is of a single T-domain, and multi-spin-rotation-domains in the film plane. The effective crystalline anisotropy of (111) NiO, calculated from micromagnetic modeling, is 2.4 × 10[sub 4] ergs/cm[sup 3]. The majority of NiO moments at the interface switched along with NiFe moments due to the low effective anisotropy, leading to a large coercivity and a low exchange field. [ABSTRACT FROM AUTHOR]

Samples with the structure Mo (20 nm)/NiFe (t nm)/NiFeMn (12 nm)/Mo (2 nm) were grown on the Al[sub 2]O[sub 3] (11–20) substrates by a MBE system. Although no magnetic field was applied during depositions, shifted hysteresis loops were observed in as-deposited samples, which were attributable to the stress-induced exchange anisotropy. With increasing thickness of NiFe, the residual stress on NiFe decreased, which resulted in the decrease of NiFe anisotropy. The exchange field decreased with increasing NiFe thickness but with a transition point at t=12nm, at which the residual stress on top of NiFe might be significantly released. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic domain configurations of microstructured permalloy exchange coupled by an antiferromagnetic (NiO) thin film is presented. NiO/NiFe bilayer micrometer array elements were fabricated using electron beam lithography through a lift-off technique. The magnetic force microscopy images of the elliptical and rectangular elements with various aspect ratios showed dipole-like magnetic domain structures. The bright/dark arc contrast associated with the magnetic pole strength was dependent on the anisotropic exchange field. Furthermore, the shape anisotropy can overwhelm anisotropic exchange in patterned elements with a high aspect ratio and thicker permalloy film. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Direct sputtering of a single quaternary Cu(In,Ga)Se2 (CIGS) target without postselenization is a promising approach to fabricating CIGS absorbers. However, the device efficiency of the quaternary-sputtered CIGS is limited to 10%-11% due to the low and uncontrollable Se supply during the quaternary sputtering process. Here, an enhanced efficiency of 14.1% is reported by directly sputtering from a CIGS target without extra Se supply followed by sequential postdeposition treatments (PDT) of NaF and KF. The effects of different post-treatments of alkali metals on quaternary-sputtered CIGS thin films are discussed in detail. A Cu-depleted surface is not observed in the quaternary-sputtered CIGS thin films after KF-PDT, different from the observation in the coevaporated CIGS, in which the Cu-depleted surface layer induced by KF-PDT enhances the efficiency. On the other hand, it is found that KF-PDT reduces Se vacancies more effectively than NaF-PDT, which could be another electrically benign behavior of KF-PDT. The effective passivation of Se vacancies after KF-PDT overcomes the Se-poor nature of the quaternary sputtering process without postselenization. Therefore, KF-PDT combined with Na doping, which is known to annihilate InCu defects, significantly improves minority carrier lifetime and cell performance. [ABSTRACT FROM AUTHOR]

Reports that Fe-doped NiO polycrystalline and {111} epitaxial films were grown by solid-source metallorganic chemical vapor deposition. Increase in exchange field for NiFe on the polycrystalline Fe-doped NiO films with Fe content up to 18.