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Kesterite solar cells often suffer from low open‐circuit voltage due to interface recombination. To address this, a passivation approach is explored using a dielectric layer between the absorber and buffer layer, coupled with a point contact structure. In this method, carrier transport is enabled through point contacts while effectively passivating regions covered by oxide. In this study, although forming point contacts on the front surface poses processing challenges, a novel solution is presented. Herein, in situ formed ZnS nanoparticles (NPs) during Cu2ZnSn(S, Se)4 (CZTSSe) absorber fabrication is utilized as a nanomask for front surface point contacts. A thin TaOx layer, acting as the passivation layer, is deposited over the CZTSSe surface with ZnS NPs by using atomic layer deposition (ALD). The selective removal of these NPs by deionized water soaking creates size‐controlled point contacts without damaging the absorber surface. In this approach, the first successful implementation of TaOx in enhancing CZTSSe solar cell efficiency, which jumps from 6.17% to 9.02% due to this strategy, is marked. The passivation mechanism involves sodium attraction during ALD, reduced interface defects, and the generation of positive fixed oxide charges. In this innovative method, not only solar cell efficiency is improved but new insights are also provided into using secondary phases as nanomasks in interface engineering. [ABSTRACT FROM AUTHOR]

Antiferromagnet (AFM) has currently participated in the spin‐orbit torque (SOT) technology due to its great potential to be applied to the field‐free SOT switching and to promote the thermal stability of MRAM. However, the effect of varying AFM ordering on the SOT switching and the associated properties is still not comprehensively understood. This work reports how an AFM ordering modifies the strength of Dzyaloshinskii–Moriya‐interaction (DMI) in a heavy metal (Pt)/FM (Co)/AFM (IrMn) trilayer and its effects on SOT switching. Increasing the AFM ordering reflects the enhanced exchange bias through increasing IrMn thickness appears to significantly reduce the DMI strength of the trilayer. Controlling the IrMn thickness appears to serve as a unique switch to activate memristivity/stochasticity in the devices via tailoring AFM ordering on exchange bias: The strong AFM ordering via increasing IrMn thickness enables to increase the stability of multi‐levels for SOT switching, which promotes the memristivity for neuromorphic application. On the contrary, the weak AFM ordering via reducing IrMn thickness will lead to significant stochasticity for the physically unclonable functionality. This work demonstrates an intrinsic tuning over the AFM ordering will serve as a switch to turn the SOT device into a stochastic/memristive cell to bridge probabilistic and neuromorphic computing. [ABSTRACT FROM AUTHOR]

Post‐selenization‐fabricated (using elemental Se vapor) Cu(In,Ga)Se2 solar cell efficiency is limited by a low open‐circuit voltage, which is attributable to the Ga‐deficient surface and insufficient grain growth. In this study, a band‐grading structure is demonstrated by combining Ag‐front and Ga‐back grading in selenized (Ag,Cu)(In,Ga)Se2 (ACIGSe) absorbers with a properly designed precursor structure (Mo/CuGa/In/AgGa) and high Ag content ([Ag]/([Ag]+[Cu]) = 0.5). The phase evolution during post‐selenization reveals that the precursor structure suppresses Ag2Se formation and promotes the ACIGSe phase formed at a low temperature with enhanced grain growth. A widened surface bandgap by Ag‐front grading substantially increases the open‐circuit voltage. Furthermore, Ag addition promotes ordered vacancy compound (OVC) formation on the front surface to enlarge the valence band offset, which in turn reduces interface recombination. Furthermore, the OVC phase also assists interface passivation. Promoting surface OVC phase by Ag addition is also validated by first‐principles calculations. Furthermore, the K‐doped CuGa precursor is used for a ACIGSe absorber to address the significantly reduced carrier density by the Ag addition. With a band‐grading structure and surface OVC phase, the superior device achieves an efficiency of > 19%, the highest efficiency by post‐selenization with an elemental Se source. [ABSTRACT FROM AUTHOR]

Neuromorphic computing based on brain-inspired frameworks has shown its potential to perform computation with remarkable power and speed efficiency. The spintronic device has been considered a promising candidate for neuromorphic computing because of its intrinsic non-volatility, ultrafast switching dynamics and scalability. This article will review the current status of neuromorphic computing techniques employing spintronic materials and devices. We will begin with a concise introduction to the biological structure of neurons and then go through several important models of artificial neural networks. The revolutionary breakthroughs of spintronic-based neuromorphic computation will be demonstrated together with their challenges and outlook. This paper will systematically review the status of neuromorphic computing techniques employing spintronic materials and devices. After reading this article, readers can grasp the revolutionary breakthroughs of spintronic-based neuromorphic computation. [ABSTRACT FROM AUTHOR]

The antiferromagnet (AFM) and ferromagnet (FM) interface is a unique branch of magnetics of broad scientific interest. AFMs play an important role in spin‐orbit torque devices based on their ability to generate spin‐polarized current and exchange bias when combined with FMs. In this study, an interesting spin‐orbit torque (SOT) ratchet involving the exchange spring effect in an IrMn/CoFeB bilayer device with perpendicular anisotropy and exchange bias is developed. The combined use of electrical and spectroscopic analysis reveals that the exchange spring in IrMn/CoFeB bilayer yields unidirectional anisotropy, resulting in a collinear/orthogonal AFM/FM spin configuration at the interface upon switching CoFeB magnetization upward/downward. The ratcheting characteristics resulting from unidirectional anisotropy manifest in SOT switching. In this process, magnetization against the exchange spring features digital‐like switching with a sharp transition, whereas the reverse function is characteristic of analog switching with a gradual transition tail. The dual digital‐analog characteristics of the IrMn/CoFeB bilayer may be of benefit in neuromorphic and memory applications. [ABSTRACT FROM AUTHOR]

Terahertz (THz) spin dynamics and vanishing stray field make antiferromagnetic (AFM) materials the most promising candidate for the next-generation magnetic memory technology with revolutionary storage density and writing speed. However, owing to the extremely large exchange energy barriers, energy-efficient manipulation has been a fundamental challenge in AFM systems. Here, we report an electrical writing of antiferromagnetic orders through a record-low current density on the order of 106 A cm−2 facilitated by the unique AFM-ferromagnetic (FM) phase transition in FeRh. By introducing a transient FM state via current-induced Joule heating, the spin-orbit torque can switch the AFM order parameter by 90° with a reduced writing current density similar to ordinary FM materials. This mechanism is further verified by measuring the temperature and magnetic bias field dependences, where the X-ray magnetic linear dichroism (XMLD) results confirm the AFM switching besides the electrical transport measurement. Our findings demonstrate the exciting possibility of writing operations in AFM-based devices with a lower current density, opening a new pathway towards pure AFM memory applications. Electrical manipulation of antiferromagnetic order is crucial for future memory devices, but existing switching schemes require a large current density. Here, the authors achieve record low current density switching in FeRh by taking advantage of its antiferromagnetic to ferromagnetic phase transition. [ABSTRACT FROM AUTHOR]

Hard/soft magnetic bilayer thin films have been widely used in data storage technologies and permanent magnet applications. The magnetic configuration and response to temperatures and magnetic fields in these heterostructures are considered to be highly dependent on the interfacial coupling. However, the intrinsic properties of each of the layers, such as the saturation magnetization and layer thickness, also strongly influence the magnetic configuration. Changing these parameters provides an effective method to tailor magnetic properties in composite magnets. Here, we use polarized neutron reflectometry (PNR) to experimentally probe the interfacial magnetic configurations in the hard/soft bilayer thin films: L10-FePt/A1-FePt, [Co/Pd]/CoPd, [Co/Pt]/FeNi, and L10-FePt/Fe, all of which have a perpendicular magnetic anisotropy in the hard layer. These films were designed with different soft and hard layer thicknesses (tsoft and thard) and saturation magnetization ( M s s o f t and M s h a r d ). The influences of an in-plane magnetic field (Hip) and temperature (T) are also studied using a L10-FePt/A1-FePt bilayer sample. Comparing the PNR results to the micromagnetic simulations reveals that the interfacial magnetic configuration is highly dependent on tsoft, M s s o f t , and the external factors (Hip and T) and has a relatively weak dependence on thard and M s h a r d . Key among these results, for thin tsoft, the hard and soft layers are rigidly coupled in the out-of-plane direction and then undergo a transition to relax in-plane. This transition can be delayed to larger tsoft by decreasing M s s o f t . Understanding the influence of these parameters on the magnetic configuration is critical to designing functional composite magnets for applications. [ABSTRACT FROM AUTHOR]

Writing using spin–orbit torque (SOT) has been widely investigated in the field of magnetic random-access memory (MRAM). Heavy metal (HM)/CoFeB/MgO is the core of this SOT-MRAM structure. The heterostructure consisting of Ta as the spin current source and CoFeB/MgO as the perpendicular magnetic anisotropy (PMA) material is the most researched structure, owing to its high tunneling magnetoresistance ratio. However, Ta is difficult to integrate into the CMOS process due to its poor thermal stability against annealing at temperatures greater than 350 °C. Currently, β-tungsten (W) is the only HM with the CoFeB/MgO system, which can provide both thermal stability and SOT switching. Nevertheless, to achieve the high resistive β phase of W is a challenging task. Here, we report another material rhenium (Re) capable of providing thermally stable PMA up to temperature 425 °C with a perpendicular anisotropic field greater than 5000 Oe; Re possesses a spin hall angle (ϴSH) of 0.065 ± 0.003, and SOT switching can be achieved with a current density around 1.36 × 1011 A/m2. Our findings pave a new avenue for the material design of perpendicular SOT-based MRAM. [ABSTRACT FROM AUTHOR]

A back-end-of-line compatible 400 °C thermally robust perpendicular spin-orbit torque magnetic tunnel junction (p-SOT-MTJ) memory cell with a tunnel magnetoresistance ratio of 130% is demonstrated. It features an energy-efficient spin-transfer-torque-assisted field-free spin-orbit torque (SOT) switching and a novel interface-enhanced synthetic antiferromagnet (SAF). The optimal SAF with a Ru (9 Å) spacer sandwiched by Co/Pt multilayers has a high SAF coupling field of 2.8 kOe. The parallel magnetic coupling between the CoFeB-based reference layer and the bottom Co/Pt multilayer is enhanced by a magnet-coupling face-centered cubic textured Co/Pt (5 Å) multilayer buffer. The thermally induced Pt–Fe interdiffusion is effectively reduced by the W (3 Å) trilayers of texture-decoupling diffusion multibarrier. The Ta/ $\beta $ -W and TaN/ $\beta $ -W composite SOT channels are thick enough to be the etching stop and sustain 400 °C annealing without transforming to $\alpha $ -W. Using the harmonic Hall voltage measurement, the Ta/W and TaN/W channels exhibit the large effective spin Hall angle of approximately −0.21 and −0.27, respectively. Scaling magnetic tunnel junction (MTJ) down to 30 nm size can reduce the switching time due to single-domain switching based on the micromagnetic simulation. The damping constant of ~0.018 is obtained by the ferromagnetic resonance measurement. A bigger damping constant reduces the switching time as predicted by the calibrated simulation. [ABSTRACT FROM AUTHOR]

Synthetic antiferromagnets (SAFs), composed of Ru spacer with a Re insertion layer, reveal superior thermal stability up to 450 °C annealing, making the back-end of line process a wider manufacturing window and tolerance to integrate the perpendicular magnetic tunneling junctions (P-MTJs) into CMOS process. The coupling strength decays significantly for SAFs with single Ru spacer after annealing above 400 °C. Due to the characteristics of refractory metals, Re can behave as a diffusion barrier during annealing. Furthermore, the Re spacer can still keep reasonable RKKY coupling strength. Therefore, the SAFs with Ru/Re composite spacers exhibit higher RKKY coupling strength than Ru spacers after 450 °C annealing. In addition, we discovered the different enhancements for the upper and lower interfacial Re insertion, which was attributed to the varied defect formation at interfaces. The stacking fault was formed at the upper Ru/Co interface in as-deposited state. When Re was inserted at the upper interface, the diffusion between Co and Ru was significantly suppressed and the stacking fault can be eliminated during annealing, leading to enhanced interlayer coupling. Through the interfacial engineering, we may have more degrees of freedom to tune the SAF performance and thus enhance process compatibility of P-MTJ to the CMOS process. [ABSTRACT FROM AUTHOR]

This work applied an anisotropic magneto-resistance effect for studying the spin–orbit torque (SOT)-driven magnetization switching in an antiferromagnetic heavy alloy/ferromagnet, PtMn/Co bilayer, under y-type SOT geometry. The tailorable magneto-structural ordering of PtMn provides an additional dimension to study the interplay among SOT efficiency, the interfacial spin configuration, and the y-type SOT switching. The results reveal that the SOT efficiency of PtMn, effective field generated by current, can be enhanced via forming the L10 (antiferromagnetic) phase after annealing; however, the efficiency appears to be less sensitive to the interfacial spin configuration. On the other hand, the critical current for the y-type SOT switching is even strongly associated with the PtMn/Co interfacial spin configuration. The lowest (highest) critical current is yielded when Co is antiferromagnetically (ferromagnetically) coupled to PtMn through the exchange bias. Engineering the interfacial spin configuration may provide an effective strategy to promote the critical current for the SOT device. [ABSTRACT FROM AUTHOR]

Severe Ga accumulation at the back contact is regarded as one of the major limiting factors for high efficiency Cu(In,Ga)Se2 (CIGSe) solar cells fabricated by the sequential process. The Ga deficiency near the front surface of absorber leads to the reduction of open‐circuit voltage; however, controlling the Ga grading is quite challenging during the selenization process. Herein, the tuning of Ga profile is demonstrated by forming the ordered vacancy compound (OVC) phase at the beginning of selenization process under high Se partial pressure (PSe) with the precursor composed of a relatively high In content. The OVC phase formed with a columnar structure promotes Ga diffusion through Cu vacancies, resulting in Ga increase at the front side of CIGSe. However, high PSe also increases the thickness of MoSe2, significantly raising the series resistance. Thereby, a 5 nm TiN layer is deposited on top of Mo to suppress the formation of MoSe2. In addition, the extra Na‐contained precursor is added to increase the carrier concentration because the TiN layer also blocks the Na outdiffusion from the substrate. By controlling PSe, interlayer TiN thickness, and carrier concentration, a 16.04% record high efficiency of CIGSe solar cells (sulfur‐free) via elemental Se source is achieved. [ABSTRACT FROM AUTHOR]

Single‐layered MoS2 is a naturally stable material. Integrating spin, valley, and circularly polarized photons is an interesting endeavor to achieve advanced spin‐valleytronics. In this study, room‐temperature ferromagnetism in MoS2 induced by the magnetic proximity effect (MPE) of yttrium iron garnet (YIG) and the antiferromagnetic coupling at the interface is demonstrated. Insulating YIG without charge carriers is an excellent magnetic candidate featuring a long spin diffusion length and remarkable surface flatness, enabling long‐range magnetic interactions with MoS2. Spin‐resolved photoluminescence spectroscopy and magnetic circular dichroism (MCD) reveal that the spin‐polarized valleys of MoS2 can achieve sustained ferromagnetism even at room temperature. The bandgap‐sensitivity of MCD further demonstrates the extent of antiferromagnetic coupling between the MPE‐induced moments of MoS2 and YIG. This work provides a layer‐selected approach to study magnetic interactions/configurations in the YIG/MoS2 bilayer and highlights the role of MoS2 in achieving the MPE toward high temperature. [ABSTRACT FROM AUTHOR]

We present a study concerning the unexpectedly large coercivity increase and associated magneto-structural properties of CoxNi1-x patterned arrays. An increase in x led to an face-center-cubic (FCC)→hexagonal-close-packed (HCP) transition in CoxNi1-x arrays, accompanied by a 6-fold increase in coercivity and strong 3d exchange interactions probed by x-ray magnetic circular dichroism. Sum-rule analysis revealed that orbital moment involved very little in the variable coercivity and magnetic anisotropy; this is distinct from other nanostructures displaying variable coercivity. The sharp rise in coercivity can be attributed to the geometrical confinement of the arrays, causing the microstructure of the nano-clusters to switch magnetization reversal mechanism from fanning to coherent with increasing x, based on the chain-of-spheres model. First-order-reversal curves revealed that the FCC and HCP arrays comprised both soft and hard ferromagnetic components; however, the soft component of the FCC was much more pronounced, leading to differences in reversibility. This type of nanostructure provides a sharp control of magnetic hardness that could be tailored in related technologies. [ABSTRACT FROM AUTHOR]

Current induced magnetization switching is of particular interest to develop non-volatile magnetic memories (MRAM). We studied spin–orbit torque (SOT) switching in a Pt/ferromagnet/antiferromagnet Pt/[Co/Ni]2/PtMn Hall cross. For the as-deposited sample, which showed no exchange bias effect, SOT switching is observed only under an in-plane applied field. In this case, when the in-plane applied field tends to zero, the current switching required diverges and the Hall voltage signal generated by the switching tends to zero. However, the same sample is annealed perpendicular to the plane and then in an in-plane applied field, which demonstrated not only square Hall voltage vs current hysteresis loops but also a moderate switching current in zero magnetic field. This procedure induces an out-of-plane exchange bias with strengthened perpendicular magnetic anisotropy and an in-plane exchange bias, which induces zero field SOT switching. The study of the SOT switching for both annealing procedures as a function of the injected current and the in-plane field is shown. These results could impact the design of future spintronics devices such as SOT-MRAM. [ABSTRACT FROM AUTHOR]

Well-aligned (001)-oriented granular or particulate L10 FePt films on amorphous SiO2 or glass substrates were obtained by depositing atomic-scale Fe/Pt/SiO2 multilayers followed by various postannealing conditions. After 350 °C annealing, (001) FePt–SiO2 granular films were obtained with an average grain size of 5.14 nm, perpendicular coercivity of 7.7 kOe, and squareness of 0.95. The diffusion of SiO2 to grain boundaries and free surface of FePt accelerated the diffusion of Fe and Pt atoms to form the L10 phase; therefore, low-temperature ordering of FePt was achieved. By further raising the annealing temperature to 700 °C, isolated particles of aligned (001) single crystals were achieved. The nucleation of voids occurred at low temperatures due to the existence of low-surface-energy SiO2, and then an agglomeration process proceeded, leading to a particulate structure. The isolated particles showed a perpendicular coercivity of 60 kOe and squareness of unity. [ABSTRACT FROM AUTHOR]

Epitaxial {111} Ni[sub 0.82]Fe[sub 0.18]O films (NiFeO) were prepared by using solid-source metal-organic chemical vapor deposition on {0001} α-Al[sub 2]O[sub 3]. The exchange anisotropy between NiFeO and Ni[sub 80]Fe[sub 20] (NiFe) was investigated. Structural and chemical analyses showed that NiFeO films were compositionally homogeneous. The 60-degree rotational twins formed in the NiFeO films. The epitaxial relationship between Ni[sub 0.82]Fe[sub 0.18]O and Al[sub 2]O[sub 3] is the following: [111] NiFeO|[0001]α-Al[sub 2]O[sub 3], [11¯0]NiFeO|[11¯00]α-Al[sub 2]O[sub 3], and [112¯]NiFeO|[112¯0]α-Al[sub 2]O[sub 3]. The orientation relationship between NiFeO and NiFe is cube-to-cube. Misfit dislocations pile up at the interfaces significantly reduce the stress, and result in semi-coherent interfaces. In-plane tension and out-of-plane compression were developed in NiFeO films due to the thermal stress, which may force the magnetic moment of NiFeO to lie in the {111} planes parallel to the film surface, and may lead to a strong interfacial coupling between NiFeO and NiFe. The relative small exchange field possibly results from (1) a low anisotropy energy compared to the interfacial coupling energy in the NiFeO {111} plane, (2) an orientation distribution of the easy axes in the NiFeO {111} plane, and (3) the large domain size of NiFeO. The Malozemoff model was used to estimate the exchange field in this system. Based on the assumption that the domain size of the NiFeO is approximately equal to the twin size, the calculated exchange field agrees well with the experimental results. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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]

(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]

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]

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]

A nanoporous Ni/NiO/C nanocomposite with a gyroid nanostructure was fabricated by using a nanoporous polymer with gyroid nanochannels as a template. The polymer template was obtained from the self-assembly of a degradable block copolymer, polystyrene-b-poly(l-lactide) (PS-PLLA), followed by the hydrolysis of PLLA blocks. Templated electroless plating followed by calcination was performed to create a precisely controlled Ni/NiO gyroid nanostructure. After carbon coating, a well-interconnected nanoporous gyroid Ni/NiO/C nanocomposite can be successfully fabricated. Benefiting from the well-interconnected nanoporous structure with ultrafine transition metal oxide and uniform carbon coating, the gyroid nanoporous Ni/NiO/C nanocomposite electrodes exhibited high specific capacities at various rates (1240 mA h g−1 at 0.2 A g−1, 902 mA h g−1 at 2 A g−1 and 424 mA h g−1 at 10 A g−1) and excellent cyclability (809 mA h g−1 at 1 A g−1 after 1000 cycles, average coulombic efficiency 99.86%). This research demonstrates a universal approach for constructing a nanostructured electrode with explicitly controlled block copolymer phase separation. [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]

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]

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]

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]

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]

The correlation between the exchange field of NiFe/NiMn and the phase transformation of NiMn was investigated. Transmission electron microscopy (TEM) dark-field images, contributed by the order phase of NiMn, were used to identify the location and volume fraction of the order phase. TEM selected area diffraction patterns showed the (110) superlattice diffraction rings of NiMn, verifying the existence of the order phase in the annealed samples. The order volume fraction can be calculated by the dark field image contributed by the (110) diffraction. The exchange field increased almost linearly with increasing order volume fraction. Energy dispersive x-ray spectroscopy attached to TEM indicated that Mn diffused into NiFe for annealing at 280 °C, leading to a larger coercivity and small coercivity squareness. Part of the NiMn still maintains the paramagnetic phase even after annealing at 280 °C. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In-plane magnetic anisotropy was studied in Co films epitaxially grown on NiMn (001) films. The hysteresis loops measured in-plane perpendicular to the exchange field show double shifted loops, and the magnetization of Co to rotate coherently. Magnetic anisotropy constants can be determined from these double shifted loops. Exchange coupling in NiMn/Co not only induces a unidirectional anisotropy but also a uniaxial anisotropy. This induced uniaxial anisotropy may contribute to the enhancement of Co coercivity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetoresistance (MR) ratio is enhanced by 35% by inserting the nano-oxide layer (NOL) at the Ta/Co interface in the FeMn-based top spin valves (Ta/NOL/Co/Cu/Co/FeMn/Ta). The enhancement is attributed to specular reflection, resulting in a large resistance change and small sheet resistance. However, the formation of NOL at the interface of Ta/Co suppresses the (111) texture, resulting in small exchange fields. Top spin valves with NOLs show good thermal stability up to 200 °C annealing. The MR ratio is further increased after annealing at temperatures below 200 °C. Enhancement of the MR ratio by 61% can be achieved by annealing at 150 °C. For bottom spin valves (Ta/NiFe/FeMn/Co/Cu/NiFe/Ta), NOLs formed at FeMn/Co and NiFe/Ta interfaces increase MR ratios, but NOLs at Co/Cu or Cu/NiFe deteriorate the differential spin scattering and significantly reduce MR ratios. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Spin valves composed of ferrimagnetic/Cu/ferrimagnetic layers were fabricated with the magnetization perpendicular to the film planes. By changing the composition of ferrimagnetic layers, both negative and positive giant magnetoresistance (GMR) can be observed in ferrimagnetic spin valves. For samples consisting of both transition-metal (TM-) rich TbFeCo and GdFeCo, negative GMR values were obtained. Due to the high resistivity of amorphous ferrimagnetic films, the shunting effect of Cu led to relatively small MR ratio. The negative MR effect was 1% for 1.7 nm Cu. For spin valves consisting of rare-earth (RE-)rich TbFeCo and TM-rich GdFeCo, positive GMR values were observed. A thin layer of Co was inserted between RE-rich TbFeCo and Cu to manipulate the sign of GMR. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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 on exchange anisotropy in Ni82Fe18O{100}/Ni80Fe20 bilayers. Examination of the exchange field for 45 A Ni80Fe20 on Ni0.82Fe0.18O films; Measurement of the atomic ratio of Fe/(Fe+Ni) film; Description of two requirements that are necessary for achieving high exchange fields; Experimental procedures of this study.

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.

Presents a study which explored the magnetization reversal and coercivity of epitaxial nitrogen oxide (III)/nickel iron films. Methods; Results; Discussion.