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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.

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 (Mssoft and Mshard). 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, Mssoft, and the external factors (Hip and T) and has a relatively weak dependence on thard and Mshard. 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 Mssoft. Understanding the influence of these parameters on the magnetic configuration is critical to designing functional composite magnets for applications.

Magnetic interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations. Here we demonstrate an extremely sensitive magnetic yoking effect and tunable interactions in FePt based hard/soft bilayers mediated by the soft layer. Below the exchange length, a thin soft layer strongly exchange couples to the perpendicular moments of the hard layer; above the exchange length, just a few nanometers thicker, the soft layer moments turn in-plane and act to yoke the dipolar fields from the adjacent hard layer perpendicular domains. The evolution from exchange to dipolar-dominated interactions is experimentally captured by first-order reversal curves, the ΔM method, and polarized neutron reflectometry, and confirmed by micromagnetic simulations. These findings demonstrate an effective yoking approach to design and control magnetic interactions in wide varieties of magnetic nanostructures and devices.

A design for the fabrication of metallic nanoparticles is presented by thermal dewetting with a chemically heterogeneous nano-template. For the template, we fabricate a nanostructured polystyrene-b-polydimethylsiloxane (PS-b-PDMS) film on a Si|SiO2 substrate, followed by a thermal annealing and reactive ion etching (RIE) process. This gives a template composed of an ordered hexagonal array of SiOC hemispheres emerging in the polystyrene matrix. After the deposition of a FePt film on this template, we utilize the rapid thermal annealing (RTA) process, which provides in-plane stress, to achieve thermal dewetting and structural ordering of FePt simultaneously. Since the template is composed of different composition surfaces with periodically varied morphologies, it offers more tuning knobs to manipulate the nanostructures. We show that both the decrease in the area of the PS matrix and the increase in the strain energy relaxation transfer the dewetted pattern from the randomly distributed nanoparticles into a hexagonal periodic array of L10 FePt nanoparticles. Transmission electron microscopy with the in situ heating stage reveals the evolution of the dewetting process, and confirms that the positions of nanoparticles are aligned with those of the SiOC hemispheres. The nanoparticles formed by this template-dewetting show an average diameter and center-to-center distance of 19.30 ± 2.09 nm and 39.85 ± 4.80 nm, respectively. The hexagonal array of FePt nanoparticles reveals a large coercivity of 1.5 T, much larger than the nanoparticles fabricated by top-down approaches. This approach offers an efficient pathway toward self-assembled nanostructures in a wide range of material systems.

A design for the fabrication of metallic nanoparticles is presented by thermal dewetting with a chemically heterogeneous nano-template. For the template, we fabricate a nanostructured polystyrene-b-polydimethylsiloxane (PS-b-PDMS) film on a Si|SiO2 substrate, followed by a thermal annealing and reactive ion etching (RIE) process. This gives a template composed of an ordered hexagonal array of SiOC hemispheres emerging in the polystyrene matrix. After the deposition of a FePt film on this template, we utilize the rapid thermal annealing (RTA) process, which provides in-plane stress, to achieve thermal dewetting and structural ordering of FePt simultaneously. Since the template is composed of different composition surfaces with periodically varied morphologies, it offers more tuning knobs to manipulate the nanostructures. We show that both the decrease in the area of the PS matrix and the increase in the strain energy relaxation transfer the dewetted pattern from the randomly distributed nanoparticles into a hexagonal periodic array of L10 FePt nanoparticles. Transmission electron microscopy with the in situ heating stage reveals the evolution of the dewetting process, and confirms that the positions of nanoparticles are aligned with those of the SiOC hemispheres. The nanoparticles formed by this template-dewetting show an average diameter and center-to-center distance of 19.30 ± 2.09 nm and 39.85 ± 4.80 nm, respectively. The hexagonal array of FePt nanoparticles reveals a large coercivity of 1.5 T, much larger than the nanoparticles fabricated by top-down approaches. This approach offers an efficient pathway toward self-assembled nanostructures in a wide range of material systems.

The A1-L10 phase transformation has been investigated in (001) FeCuPt thin films prepared by atomic-scale multilayer sputtering and rapid thermal annealing (RTA). Traditional x-ray diffraction is not always applicable in generating a true order parameter, due to non-ideal crystallinity of the A1 phase. Using the first-order reversal curve (FORC) method, the A1 and L1 0 phases are deconvoluted into two distinct features in the FORC distribution, whose relative intensities change with the RTA temperature. The L10 ordering takes place via a nucleation-and-growth mode. A magnetization-based phase fraction is extracted, providing a quantitative measure of the L10 phase homogeneity. © 2014 Author(s).

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 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.