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Understanding the mechanisms of unidirectional magnetoresistance (UMR) has become an important topic for its potential application of a two-terminal spin–orbit torque device. Field sweep DC measurements have been proposed and adopted to measure the value of UMR instead of second harmonic measurements. In this paper, potential measurement errors in conventional DC measurements are investigated. Oersted field and field-like torque usually do not influence the measurement, but a large field-like torque was found to lead to an anisotropic magnetoresistance difference when the sample is not perfectly aligned with the external field. The existence of ordinary magnetoresistance was also found to contribute to a large background. In this paper, an alternative measurement method for UMR was proposed and demonstrated to address those issues related to previous DC measurements. Our work may broaden the understanding of the error sources of UMR measurements and provide a reliable DC measurement method for the characterization of UMR.

Recent advancement in the switching of perpendicular magnetic tunnel junctions with an electric field has been a milestone for realizing ultra-low energy memory and computing devices. To integrate with current spin-transfer torque-magnetic tunnel junction and spin–orbit torque-magnetic tunnel junction devices, the typical linear fJ/V m range voltage controlled magnetic anisotropy (VCMA) needs to be significantly enhanced with approaches that include new materials or stack engineering. A possible bidirectional and 1.1 pJ/V m VCMA effect has been predicted by using heavily electron-depleted Fe/MgO interfaces. To improve upon existing VCMA technology, we have proposed inserting high work function materials underneath the magnetic layer. This will deplete electrons from the magnetic layer biasing the gating window into the electron-depleted regime, where the pJ/V m and bidirectional VCMA effect was predicted. We have demonstrated tunable control of the Ta/Pd(x)/Ta underlayer's work function. By varying the Pd thickness (x) from 0 to 10 nm, we have observed a tunable change in the Ta layer's work function from 4.32 to 4.90 eV. To investigate the extent of the electron depletion as a function of the Pd thickness in the underlayer, we have performed DFT calculations on supercells of Ta/Pd(x)/Ta/CoFe/MgO, which demonstrate that electron depletion will not be fully screened at the CoFe/MgO interface. Gated pillar devices with Hall cross geometries were fabricated and tested to extract the anisotropy change as a function of applied gate voltage for samples with various Pd thicknesses. The electron-depleted Pd samples show three to six times VCMA improvement compared to the electron accumulated Ta control sample.

Bulk gallium oxide (Ga2O3) has been widely used in lasers, dielectric coatings for solar cells, deep-ultraviolet transistor applications due to the large band gap over 4.5 eV. With the miniaturization of electronic devices, atomically thin Ga2O3 monolayer has been unveiled recently, which features an asymmetric configuration with a quintuple-layer atomic structure. The superior stability, the strain-tunable electronic properties, high carrier mobility and optical absorption indicate the promising applications in the electronic and photoelectronic devices. However, the strict investigation of lattice thermal conductivity (kappa_L) of 2D Ga2O3 is still lacking, which has impeded the widespread use in practical applications. Here, we report the computational discovery of low kappa_L with a value of 10.28 W m-1 K-1 at 300 K in atomically thin Ga2O3. Unexpectedly, two quasi-acoustic shear phonon modes contribute as high as 27% to the kappa_L at 300 K, leading to 37% contribution of optical phonon modes, much larger than many other 2D materials. We also find that the quasi-acoustic shear mode can emerge in the system without van der Waals interactions. This work provides new insight into the nature of thermal transport in non-van der Waals monolayer materials and predicts a new low kappa_L material of potential interest for thermal insulation in transistor applications.

We show that a surface acoustic wave (SAW) applied across the terminals of a magnetic tunnel junction (MTJ) decreases both the (time-averaged) parallel and antiparallel resistances of the MTJ, with the latter decreasing much more than the former. This results in a decrease of the tunneling magnetoresistance (TMR) ratio. The coercivities of the free and fixed layer of the MTJ, however, are not affected significantly, suggesting that the SAW does not cause large-angle magnetization rotation in the magnetic layers through the inverse magnetostriction (Villari) effect at the power levels used. This study sheds light on the dynamical behavior of an MTJ under periodic compressive and tensile strain.

The formation mechanism of α″-Fe16N2 phase was investigated in the form of nanoparticles. Both α-Fe and γ-Fe2O3 nanoparticles were used to prepare α″-Fe16N2 by using a low-temperature nitriding process (≤180 °C). The synthesized α″-Fe16N2 nanoparticles have a high α″-Fe16N2 volume ratio up to 93%, with a specific saturation magnetization of 178 emu/g (room temperature) and coercivity of 2.0 kOe. The formation of α″-Fe16N2 phase includes three stages: (1) the heterogenous nucleation of α″-Fe16N2 with simultaneous chemical reaction, (2) the growth of α″-Fe16N2 with a local electric field in the Fe16N2 layer, and (3) the termination of Fe16N2 growth due to the nucleation of other Fe–N phases (e-Fe3N or γ′-Fe4N). In low-temperature nitriding, NH3 was used as the nitrogen source. The adsorbed NH3 molecules on the Fe surface decompose into N and H atoms, and then N atoms react with Fe and nucleation of α″-Fe16N2 simultaneously occurs at the high-energy surface sites of reduced Fe nanoparticles. The growth of α″-Fe16N2 phase can be explained by the electric field modified diffusion theory, where the electric field is established by the migration of Fe and N ions and electrons. Finally, the nucleation of Fe–N stable phases (e-Fe3N or γ′-Fe4N) ceases the further growth of α′′-Fe16N2 layer. Then, there is critical thickness for the α″-Fe16N2 layer, which is estimated to be 10–15 nm from the surface. Therefore, single-phase α″-Fe16N2 nanoparticles are expected in fine particles with less than 30 nm in diameter.

Benefitting from low propagation loss and complementary metal–oxide–semiconductor compatibility, Si 3N 4 is heavily explored for the applications of nonlinear optical signal processing. However, the Si 3N 4 waveguide is limited by its low optical Kerr nonlinearity. In this work, we introduce highly nonlinear ultra-Si-rich-nitride (USRN) deposited by the plasma enhanced chemical vapor deposition system. The measured linear refractive index of USRN is 3.09 at a wavelength of 1550 nm, while the Kerr nonlinearity of the USRN waveguide is experimentally extracted with a value of 2.25 × 10 − 17 m 2/W. Moreover, a broadband wavelength conversion ranging from S-band to L-band by a four-wave-mixing experiment is realized via designed USRN waveguide with a relatively short length of 3 mm. The measured bandwidth is 190 nm with a continuous-wave pump laser located at 1530 nm. The conversion efficiency is measured approximately − 48 dB under a relatively low pump power of 7 dBm.

Ejecta is produced from the shock-loaded perturbed surface of metals and subsequently breaks into small particles that are an important source of micro-particles/gas mixing during ejecta's transport and conversion. In engineering applications, the surrounding gas is often neglected during ejecta's formation, and many source models have been established based on the vacuum condition. However, the formation of the spike is always accompanied by gas, which has an important effect on the ejecta's mass/velocity distribution and the transformation time for a steady-state shock wave. To study the interaction between ejecta and ambient gases, we explore the ejecta production at the sinusoidal interface in the presence of argon gas. Six values of gas pressure and five interfaces were chosen to study the formation of the spike/micro-jet by using multi-component elastic–plastic hydro-dynamic codes. The results show that gas perturbed by the spike generated a precursory bow-shaped shock and gradually transformed into a plane wave. The transformation time was related to the velocity of the spike tip and the transmitted wave. The total mass of ejecta in gas had no distinct difference with that in vacuum, while it was significantly increased at the jet tip, which indicates that gas resistance reduced the spike velocity but did not influence the bubble. The initial velocity of the spike was insensitive to gas pressure but its decaying rate was positively correlated with gas pressure. As kh0 increased, the initial velocity of the spike tip and its decaying range increased, making it difficult to attain a steady state.

Cellular-level neuron stimulation has attracted much attention in the areas of prevention, diagnosis and treatment of neurological disorders. Herein, we propose a spintronic neurostimulator based on the domain wall movement inside stationary magnetic nanowires driven by the spin transfer torque. The electromotive forces generated by the domain wall motion can serve as highly localized stimulation signals for neuron cells. Our simulation results show that the induced electric field from the domain wall motion in permalloy nanowires can reach up to 14 V/m, which is well above the reported threshold stimulation signal for clinical applications. The proposed device operates on a current range of several uA which is 10^3 times lower compared to magnetic stimulation by microcoils. The duration and amplitude of the stimulating signal can be controlled by adjusting the applied current density, the geometry of the nanowire, and the magnetic properties of the nanowire material., Comment: 11 pages, 4 figures

Magnetic tunnel junctions (MTJs) operating in the superparamagnetic regime produce telegraphic signals that emulate neural spiking signals. Previous studies have characterized the random spiking signals produced by MTJs in terms of the percentage of time spent in the anti-parallel (AP) magnetization state (referred to as the “AP rate”) but ignore the switching rate of the MTJ. In this work, we demonstrate that with proper tuning of both an external bias field and a bias voltage, we can control the average dwell time in the AP-state and P-state pulses separately. Our data show that the AP rate can be tuned with bias voltages ranging from 310 mV to 460 mV and bias fields from −200 Oe to −230 Oe. The average dwell times in each state ranged from 225 ns to 285 μs and could be controlled separately. This suggests that neural spiking signals produced by MTJs can be decoded by both the spike rate and the spike count, which creates the possibility for increasing the information capacity in the rate coding scheme.

We report on the effect of varied capping layers on the formation of thin film MnBi, and the associated magnetic and crystalline properties for use in magnetic memory. MnBi thin films with a capping layer of either Ta, SiO2, Cr, or Au were grown, and it was observed that the magnetic properties vary significantly depending on the capping layer. Continuous 20 nm MnBi thin films capped with Ta and SiO2 show ferromagnetism with large perpendicular magnetocrystalline anisotropy, however, films capped with Cr and Au show no ferromagnetic behavior. In this work, MnBi thin films have been characterized utilizing magnetization vs. field, x-ray diffraction, cross-section transmission electron microscopy, and optical microscopy. We show that the capping layer plays a significant role in the formation of the low temperature phase MnBi structure and propose that the underlying cause is due to a surface energy difference for the MnBi//Au and MnBi//Cr interface, which allows for Mn oxidation, and prevents the formation...

Exchange coupling constant (J) is an important magnetic parameter for the design of the antiferromagnetically coupled medium. So far, the relationship between the exchange bias (Hex) and exchange coupling constant, Hex=J/Mst, which is deduced from the ferromagnetic–antiferromagnetic coupled system under some conditions, was commonly used to estimate the exchange coupling constant J for such medium. This article first deduces an accurate equation of the exchange coupling constant (J) and the exchange bias Hex for the antiferromagnetically coupled medium in different applied field directions. After considering the effect of easy axis distribution of the magnetic grains in the recording medium, the equation for the antiferromagnetically coupled medium is further revised as Hex=aJ/Mst. a is a constant and depends on the easy axes distribution of magnetic grains, the exchange coupling constant, and the ratio of magnetic parameters between the two magnetic layers. a is found to range from 0.2 to 0.5 for isotrop...

Interparticle interaction among single domain nanosize magnetic particles embedded in nonmagnetic matrix was studied. Attention was paid to concentrated Cu–Co granular thin films with a fixed magnetic volume fraction (20%). By analyzing theoretical models and comparing with experimental results, a dimensional constraint on the magnetic properties was found. As the film thickness reduces toward the thin limit the interparticle interaction plays important roles in modifying the magnetic behavior. The dipolar interaction energy was calculated among magnetic particles including far-neighbor interaction for films with different thickness values. When magnetization variation is included in the calculation, the resulting calculated interaction energy versus film thickness shows remarkable agreement with the variation of experimental observed peak temperature derived from magnetic blocking curves.

Ordered FePt thin films with face-centered-tetragonal (fct)-(001) preferred orientation have been prepared by magnetron sputtering a FePt layer onto a Cr91Ru9 underlayer. The effects of a Pt buffer layer between the CrRu underlayer and FePt layer on the structural and magnetic properties of the FePt films were investigated. The long range ordering parameter increases as the thickness of the Pt buffer layer increases from 0 to 4 nm. Further increase in the Pt buffer layer thickness (6 nm) causes the decrease of the ordering parameter. The out-of-plane coercivity of the films increases linearly with the increase of the thickness of the Pt buffer layer. Upon introduction of a 4 nm Pt buffer layer the number of defects in the FePt films are decreased drastically. The changes in the structural and magnetic properties of FePt films are related to the suppression of the Cr diffusion by the Pt buffer layer.

Laser-induced structural decompositions of hydrogenated amorphous carbon films deposited by dc-magnetron sputtering on magnetic hard disks were studied using a microbeam Ar+ laser (514.5 nm). The laser had varying powers between 3.0 and 0.3 mW at a focused circular spot of 2.5 μm diameter, corresponding to approximate fluence rates between 6×104 to 6×103 J cm−2 s−1. The effect of laser power on decomposition rate could be expressed by an exponential equation. Based on the relationship between laser power and temperature, relative apparent activation energies for film decompositions were obtained and found to decrease with the increase of film hydrogen content and the elapse time of laser irradiation. All the films irradiated with laser powers between 0.75 and 0.3 mW followed the apparent first-order reaction. The reaction order tended to increase at higher laser powers and hydrogen content in the films.

On the basis of a micromagnetic model, magnetization reversal in antiferromagnetically coupled (AFC) binary and ternary layers has been represented by computer simulation. Optimization of media parameters of the AFC layers has been done, especially for the effect of parameters, such as anisotropy and coupling magnitude, on the reversal. The results specify that easy axis dispersion rather than random anisotropy and a reasonably small anisotropy magnitude of the recording layer are required for obtaining large coercivity, small saturation field, and thermal stability in the AFC layers. The difference between the AFC binary and ternary structures is discussed briefly.

This study investigates the effects of CrAl underlayer and intermediate layer on the magnetic properties, crystallographic texture, and thermal stability of CoCrPtTa thin film media. Enhancement of coercivity and thermal stability factor of CoCrPtTa/CrAlx thin film media were observed when the Al concentration in the CrAl underlayer was varied from 0 to 14 at. %. We also observed an improvement in the in-plane crystallographic texture and a reduction in the magnetic switching volume and intergrain interaction. Results from the interdiffusion study using Auger depth profiling analysis, and ΔM measurement showed that the decrease of switching volume and intergrain interaction may be attributed to Al diffusion and/or Al-enhanced Cr diffusion into the grain boundary of the magnetic layer. Compared to CoCrPtTa/Cr media, we found that high coercivity, good in-plane crystallographic texture, and magnetic isolation for CoCrPtTa/CrAl media could be achieved at lower substrate temperature. This study has also shown...

This report introduces a local-magnetic-reversal-nucleation based giant magnetoresistance (GMR) sensor with a large sensing area and further discusses its novel sensing scheme of high magnetic moment nanoparticles (MNPs). We demonstrated experimentally that this large-area GMR sensor could successfully detect high moment MNPs. The detection scheme of localized reversal nucleation of GMR sensor induced by MNPs was analyzed and further confirmed by the micromagnetic simulations. This work may provide one pathway in designing next generation GMR biosensors with large area and high sensitivity. This sensing scheme could be applicable to other magnetic biosensors such as magnetic tunnel junction sensors and planar Hall sensors.

The effect of thermal energy (kBT), which has been found to play some important roles in the magnetic properties of recently developed antiferromagnetically coupled media, is described. It was observed that the thermal energy helps to obtain an antiparallel configuration of moments at remanence. Therefore, a reduction in the remnant moment–thickness product (Mrδ) is observed, even for smaller values of J (interface coupling constant) than those used in simulations that do not consider thermal energy. The magnetic viscosity measurement helps to distinguish the magnetization decay behavior of the top and bottom layers. The magnetic moments of top and bottom layers show maximum decay at different fields and the decay rates approximately scale with their thickness. Viscosity results also point out that the magnetization reversal of the bottom layer should occur in the first quadrant, in order to obtain a low noise and thermally stable media. Micromagnetic simulation was performed by including thermal effects....

Magnetic and structural properties of hexagonal-close-packed-(CoCrPt)100−xCx thin films for potential applications in magnetic recording media have been investigated. CrTi and Cr underlayers were used to improve the in-plane preferred orientation. High coercivity of 4.4 kOe and anisotropy of 3.6×106 erg/cm3 have been achieved in films with a CrTi underlayer after postdeposition annealing. The addition of Ti to the Cr underlayer results in lower annealing temperature and shorter annealing time, while retaining higher coercivity. Vibrating sample magnetometer measurements showed that the magnetic moment lies fairly well in the film plane under proper preparation conditions; while x-ray diffraction measurements showed that the CrTi underlayer promoted Co (10.0) in-plane preferred orientation. Grain isolation in the magnetic layer was improved by the segregated C and further enhanced by postdeposition annealing. The peak value of δM curves decreased upon annealing and changed to a negative value when higher a...

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite with assistance of nitrogen ion beam bombardment. X-ray photoelectron spectroscopy, Raman spectroscopy, and ellipsometry were used to identify the binding structure, nitrogen content, and optical properties of the deposited thin films. The influence of the nitrogen ion beam energy on the compositional, electronic, and optical properties of the deposited thin films was investigated. The thin films deposited with nitrogen ion bombardment had an N/C ratio of 0.43. Raman spectroscopy measurements indicated the formation of CN triple bonds in the deposited thin films. The optical band gap Eopt was observed to decrease with the nitrogen ion energy. A nitrogen ion energy between 50 and 100 eV was deduced to be the optimal condition for depositing the carbon nitride thin films.

Multilayered Co-doped TiO2 thin films with postannealing treatment were investigated. Based on x-ray photoelectron spectroscopy, Co(II) binding state was found after annealing. Its intensity increases with the annealing temperature. Postannealing in an ultrahigh vacuum system is an efficient way to drive Co atoms to diffuse into TiO2. It is interesting to find that samples with partial cosputtering structure have a much stronger Co(II) peak than those of pure multilayer structure. Transmission electron microscope patterns show that the annealed films have a polycrystal rutile-TiO2 phase. The saturation magnetization of annealed sample at 150 K is 1.325 uB per Co atom, which is close to the value expected for low-spin Co(II).

We present a simple fabrication of FePt and Fe nanocomposite by annealing self-assembled FePt nanoparticles. 5 nm FePt nanoparticles were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in the presence of oleic acid and oleylamine as stabilizers. The as-synthesized FePt nanoparticles can self-organize well on a clean SiO/Si substrate and, then, were annealed in a vacuum using a rapid thermal process at different temperatures for 0.5 h. It is found that the annealing temperature plays a key role in determining the final products. The samples annealed at 550 °C and 700 °C consist of a FePt-face-centered-tetragonal (fct) phase with a coercivity of around 1000 and 8800 Oe, respectively, whereas, the samples annealed at 580 °C are composed of two phases: one is the FePt-fct phase and the other is a Fe-body-centered-cubic phase. The hysteresis loop of the sample annealed at 580 °C is also two-phase like with a kink at low field and its coercivity is...

In this article, the magnetization reversal process and thermal stability of perpendicular coupled film glass/Ti 40 nm/CoCrPtB 35 nm/CoDy 20 nm/Ti 4 nm were presented. The exchange coupling constant with Dy content near the compensated point is as high as 1.3 erg/cm2. The dependence of exchange coupling strength on the Dy content and the thickness of CoDy layer was investigated. The thermal stability of the coupled films showed an increase over 100%.

The effects of postdeposition annealing on the structural properties of CoCrPt/Ti magnetic thin films were investigated. The improvement of out-of-plane coercivity and squareness resulted from enhancement of both the crystallinity and texture of the CoCrPt (002) peak. The initial growth region of the CoCrPt layer and the Ti underlayer greatly improved in structural and magnetic properties through annealing.

Improved coercivity was achieved in perpendicular 10-nm-thick FePt film through an inserted Ag layer. The out-of-plane coercivity increased with increasing Ag thickness, from 2.0 kOe, for the sample without Ag, to 4.4 kOe, for the sample with 3 nm Ag. Silver insertion also reduced the magnetic grain size and affected the magnetic reversal mode in these films.

This work explores the thickness dependence of magneto-transport properties in Cu80Co20 granular thin films with different thickness. These results are compared with silver-based film series studied earlier. It was observed that the thickness dependence of the GMR effect was sensitive to the surface chemistry of the films. The extraordinary Hall effect (EHE) in these films was measured and found to be different from the Ag-based system. In the Cu-based system, the EHE is a weak function of film thickness over the range studied. When the variation of the spontaneous magnetization is taken into account the effective EHE has a universal thickness dependence.

The spin orbital torques in Ta/CoFeB/MgO structures are experimentally investigated utilizing the planar Hall effect and magnetoresistance measurement. By angular field characterization of the planar Hall resistance at ±current, the differential resistance which is directly related to the spin orbital torques is derived. Upon curve fitting of the analytical formulas over the experimental results, it is found that the anti-damping torque, also known as spin Hall effect, is sizable while a negligible field-like torque is observed. A spin Hall angle of about 18 ± 0.6% is obtained for the Ta layer. Temperature dependent study of the spin orbital torques is also performed. It is found that temperature does not significantly modify the spin Hall angle. By cooling down the sample down to 100 K, the obtained spin Hall angle has a maximum value of about 20.5 ± 0.43%.

The processional magnetization induced spin current at the interface between CoFeB and Ta has been studied experimentally using spin pumping and inverse spin Hall effect for different thicknesses of CoFeB film down to 1.6 nm. It is found that upon decreasing the thickness of the CoFeB, the frequency of the peak position of the spin pumping signal reduces and dispersion relation of the ferromagnetic resonance changes from a quadratic to a linear behavior indicating the presence of an interfacial perpendicular anisotropy. Furthermore, a nonreciprocal behavior between the spin pumping signal amplitude at positive and negative fields is observed which could be as large as 100%. Our experimental results suggest reduction of the effective demagnetization field and possibly the spin waves nonreciprocal behavior mediated by the Dzyaloshinskii-Moriya interaction at the Ta/CoFeB interface are responsible for the large nonreciprocity of the spin pumping signal.

Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. The mechanism of the absorption is a charge-transfer optical transition. The relationships among the blueshift, valence state of cerium ions, and the particle size are formulated. The blueshifts are well explained for diameters down to less than a few nanometers by the change in the electronic band structure.

The effect of NiAl intermediate layer on structural and magnetic properties of L10 FePt films with perpendicular anisotropy has been investigated. It is found that the crystallographic (001) texture of face-centered tetragonal-FePt films is improved after introducing a NiAl intermediate layer. The degree of the ordering and the coercivity of the fct-FePt films increase with NiAl intermediate layer thickness. The improvement of the crystallographic texture and magnetic properties may be attributed to the effective suppression of Cr diffusion from the underlayer. The grain size of FePt films with 4 nm of NiAl intermediate layer is about half of that of FePt film without NiAl intermediate layer.

The structure and interface of Co74Cr16Pt10 (40 nm thick)/Ti (10 nm thick) films for perpendicular magnetic recording were studied using x-ray scattering and transmission electron microscopy. Improved out-of-plane coercivity and squareness resulted from the combined effects of higher crystallinity and better texture of the CoCrPt (002) film, and increased interface roughness. The relationship of sputtering pressure to the structural effects is discussed.

Annealing effects on the microstructure and magnetic properties of CoZr thin films are investigated in this article. It was found that a change in magnetic phase occurs by annealing the as-deposited films at temperatures of above 550 °C for 2 h. A much lower annealing temperature and shorter annealing time are needed to obtain a hard magnetic phase in thin films than in rapidly quenched CoZr bulk samples. Hard magnetic phase Co11Zr2 and ferromagnetic phase Co23Zr6 formed after annealing. All the annealed films show perpendicular magnetic anisotropy.

(Co60C40)97Ta3 and Co60C40 films with thickness 30 nm were prepared by cosputtering Co, Ta, and C onto C-buffered glass substrates. The as-deposited (Co60C40)97Ta3 and Co60C40 films were amorphous and nonferromagnetic. These films became magnetic upon annealing and the magnetic performance of annealed (Co60C40)97Ta3 films are better than that of annealed Co60C40 films at the same annealing condition. Magnetic patterning (line array) of the as-deposited (Co60C40)97Ta3 films was realized by subjecting it to electron-beam radiation using a focused 30 keV beam with a current of 7.1 nA and a dwell time per line of 0.75 s and longer. By increasing the dwell time, the whole region where an electron beam was scanned became magnetic with clear domain structures because of thermally activated diffusion. The required dwell time of magnetically patterning nonmagnetic (Co60C40)97Ta3 thin films (0.75 s) is much shorter than that of Co60C40 films (3.8 s). The magnetic measurements show that the lines [(Co60C40)97Ta3] an...

We have successfully demonstrated longitudinal recording at areal density of 130 Gb/in2 at a data rate as high as 170 Mbps (21 MB/s) and at a bit-aspect-ratio (BAR) of 2.9, using merged inductive-write/spin-valve-read heads on low noise thin film disks. The heads were fabricated with the standard photolithography and wafer pole trimming used in our currently available commercial products. The reader is a bottom synthetic spin valve (BSSV) with a 0.09 μm gap, and the writer has a conventionally trimmed pole with 0.09 μm gap. The reader magnetic read width (MRW) was measured at 0.10 μm. At read bias of ∼4 mA we measured reader sensitivity as high as 20 mV/μm. The write head was also optimized for tracks as narrow as 0.14 μm operating at overwrite (OW) of 36 dB and nonlinear transition shift (NLTS) better than −25 dB at 610 kBPI, without precomp. Using conventional media we measured total spectral SNR∼18 dB. The media to electronics noise ratio was 4.8, showing that we are still operating in a media noise li...

The face-centered-tetragonal-(001) FePt thin films were prepared by dc magnetron sputtering Fe50Pt50 layer onto Cr91Ru9 underlayer at 400 °C. In order to enhance the coercivity and to obtain a relative lower exchange coupling medium with nucleation reversal mechanism, a nonmagnetic Ru pinning layer inserted in the magnetic layer is described to introduce controllable defects to impede domain-wall motion. A 60% increasing of the out-of-plane coercivity was observed after 1 nm Ru nonmagnetic pinning layer added between the FePt magnetic layers. From angular dependence of the coercivity measurement, the magnetization reversal mechanism was observed to shift from the typical domain-wall motion behavior to the nucleation mode by increasing the thickness of the pinning layer.

FeTaN/TaN/FeTaN sandwich films, FeTaN/TaN and TaN/FeTaN bilayers were synthesized by using RF magnetron sputtering. The magnetic properties, crystalline structures, microstructures and surface morphologies of the as-deposited samples were characterized using angle-resolved M-H loop tracer, VSM, XRD, TEM, AES and AFM. An evolution of the in-plane anisotropy was observed with the changing thickness of the nonmagnetic TaN interlayer in the FeTaN/TaN/FeTaN sandwiches, such as the easy-hard axis switching and the appearing of biaxial anisotropy. It is ascribed to three possible mechanisms, which are interlayer magnetic coupling, stress, and interface roughness, respectively. Interlayer coupling and stress anisotropies may be the major reasons to cause the easy-hard axis switching in the sandwiches. Whereas, magnetostatic and interface anisotropies may be the major reasons to cause biaxial anisotropy in the sandwiches, in which magnetostatic anisotropy is the dominant one., Comment: 6 pages, 3 figures

By cosputtering Ag with FePt on a Cr90Ru10 underlayer, the film texture and magnetic easy axis were successfully changed from the perpendicular to the longitudinal direction. The crystallographic structure and magnetic properties of Ag-doped FePt thin films were investigated. Doping of Ag in FePt films led to greater in-plane coercivity and smaller magnetic grain size. The in-plane coercivity of the nanocomposite films varied from 0.8 to 6.5 kOe, depending on the Ag content. With an increase in Ag content, the FePt grain size became smaller, and the magnetic reversal mechanism approached the nucleation mode. These results suggest a practical way by which to fabricate L10 FePt thin films with longitudinal anisotropy using a nanocomposite approach.

Mn‐ and Co‐doped acicular γ‐Fe2O3 particles with a coercivity of 923 Oe and Co content of 3.5 wt % have been prepared by a special process. This involves high‐temperature ion diffusion, then step annealing. These particles exhibit a high magnetic thermal stability and low‐temperature coefficient of coercivity. The latter demonstrates a striking contrast to the ordinary cobalt‐body‐doped γ‐Fe2O3 particles. The induced uniaxial anisotropy constant Ku and the magnetocrystalline anisotropy constant K1 of the particles were determined by torque measurements. The novel properties of these particles are mainly due to the high uniaxial anisotropy, resulting from the anisotropic arrangements of cobalt ions. With the above characteristics and low Co content, these acicular particles can be one of the promising candidates for particulate high‐density magnetic recording materials.

Iron clusters containing from a few atoms to a few hundred atoms dispersed in a silica matrix have been prepared by a sol‐gel method with very low iron concentration, which was determined by the x‐ray‐diffraction, electron selected‐area diffraction, and magnetic measurements. Magnetic measurement shows that the magnetic moment per atom of these clusters is higher than that of bulk iron and the magnetic behavior of these clusters is well described using the theory of superparamagnetism.

On the basis of a micromagnetic model, magnetization reversal in two antiferromagnetically coupled ferromagnetic layers (10 nm t1/0.9 nmM/t2 nm films with t2=2, 3, 4, 5 nm, here t1 and t2 are the top and bottom layers, respectively, and M the spacer) with the same random anisotropy arrangement can be represented by a computer simulation. The calculation indicates that the appearance of a full antiferromagnetic coupling at remanence requires the antiferromagnetic coupling constant j=−3.5 erg/cm2 for the 10 nm t1/0.9 nmM/3 nm t2, films and it needs a large j value if t2 increases for the case of Ku2=Ku1=1×106 erg/cm3 and Ms1=Ms2=400 emu/cm3. Hc follows the equation Hc=−0.755j/Mst1 (j

We have investigated how the presence of a defect in two coupled quasi‐one‐dimensional quantum wires influences the propagation properties of guided electron waves in the system. The defect potential in the two dimensional electron gas is modeled by a two dimensional δ function. In elastic scattering, the transfer of the electron among various eigenstates of the uncoupled quantum wires and from one wire to the other is largely affected by the defect potential. For the single mode shallow potential well system, the defect causes incomplete energy transfer between the channels. As the position of the defect varies along the channel, the characteristics of the mode amplitude functions change dramatically as the defect passes through nodes of the amplitude function of the incident waves in the channel. When the defect position is away from these nodes the amplitude functions of the transmitted waves reduce greatly due to the large reflection by the defect. And their variation never reaches zero as in the case...

In this article, we report the magnetic properties of surfactant coated γ-Fe2O3 nanoparticles which are pressed under different pressures. With increasing pressure, the sample volume decreases, density increases, and a 55% density change has been achieved. The blocking temperature is increased from 50 to 80 K. Analyzing the data of blocking temperature versus densities, which exhibits linear relationship, and comparing the magnetic properties, the increase in blocking temperature is understood in terms of increased magnetic interactions between neighboring nanoparticles, which is due to the reduced average interparticle distance by the applied pressure.

The effect of CoCrTa intermediate layer and postannealing on the magnetic properties and microstructure of CoCrPt/Cr thin film media has been investigated. Through a postdeposition annealing in a vacuum oven, a tremendous increase of coercivity up to 6000 Oe was observed for these CoCrPt/CoCrTa/Cr films, in which the thickness of CoCrTa intermediate layer is about 2.6 mm. X-ray diffraction results showed that the hexagonal-close-packed crystallographic structure for the cobalt alloy did not show any change for the sample after postannealing. In-plane transmission electron microscope images for the CoCrPt/CoCrTa/Cr films showed no change of the morphology before and after annealing and about 15% increase of the grain size for the films after annealing. Delta M curves and remanent squareness results showed that intergrain diffusion may result in this improvement of magnetic properties. Atomic force microscope images showed that the surface roughness for the sample after annealing was almost the same as that...

The effects of anisotropy axes distribution on the properties of longitudinal recording media are simulated using the micromagnetic modeling. The angle between the anisotropy axis and the preferred direction is assumed to follow the Gaussian distribution. Hysteresis loops are simulated with the field applied in the preferred direction and perpendicular to it. Orientation ratios (OR) are calculated for different anisotropy distribution. OR (coercivity) increased from 1.4 to 79.2 when standard deviation of anisotropy distribution σ decreased from 0.7 to 0.05. The effect of the anisotropy distribution on the recording performance is evaluated, too. The results show that narrowing the anisotropy distribution will increase the OR and decrease the transition noise power and transition length. It was found that a critical point occurred at σ=0.15, below which the OR can be maintained at a sufficiently high value and yet the integrated noise power can be kept low.

A metal layered structure consisting of Cr/Cu buffer layer and two Co layers with different thickness, separated by a Cu spacer, was deposited on Si wafers using magnetron sputtering. The influence of the individual layer’s thickness on the magneto transport and magnetic hysteresis was studied. Optimization of the magnetoresistance performance was supported by the current in-plane giant magnetoresistance (GMR) modeling based on the solution to the Boltzmann transport equation. The best structures demonstrated very sharp magnetization reversal of the lower Co layer at about 100 Oe accompanied by resistivity change with a rate of 0.9%/Oe. Maximum GMR effect measured at 5 K was 9.6%. Samples with capping layers exhibited substantially smaller switching fields of the upper Co layer than the uncapped samples with a minute amount of CoO.

The role of amorphous Ni50P50 as a precoating layer in CoCrPtTa/Cr/glass substrate thin film media has been studied. It was found that the amorphous NiP layer has a strong effect on grain size reduction. Both in-plane transmission electron spectroscopy (TEM) images and atomic force microscopy images reveal a large reduction of the average grain size of the Cr underlayer deposited on the precoating Ni50P50 layer compared to the one on a glass substrate. The TEM images also show that Ni50P50 film has isolated unique granular features approximately 10 nm in diameter, consisting of grains with uniform size that could be inherited by the subsequent layers. Samples with NiP precoating layer on the glass substrate show a slightly higher surface roughness that may be attributed to the smaller Co grains induced. Magnetic force microscopy images at remanent state also indicate a much smoother micromagnetic structure for media with a NiP precoating layer.

Magnetic properties and microstructure of granular CoCrPt–SiO2 thin films with Cr underlayers have been investigated for potential applications in magnetic recording media. The coercivities exceeding 2500 Oe have been obtained in the as-deposited films with SiO2 varied from 8 to 16 vol %. Remarkable improvement in magnetic properties was achieved by postdeposition annealing in vacuum. The ultrahigh coercivity up to 5640 Oe was obtained in the lower SiO2 content film (CoCrPt)96(SiO2)4 which was annealed at 580 °C for 10 min. The annealing did not induce significant grain growth. The average grain size varied from 10 to 20 nm, depending on SiO2 concentration. Grain isolation in magnetic layer was achieved by the segregated SiO2 and further enhanced by annealing. The ac demagnetized magnetic clusters, observed by magnetic force microscopy, became very fine after annealing. The peak value of delta M curves changed from positive to negative value, indicating a great reduction of intergrain magnetic exchange co...

Aluminum nitride (AlN) thin films were deposited by nitrogen-ion-assisted pulsed laser ablation of an AlN target. A KrF excimer laser with a pulse duration of 23 ns and a wavelength of 248 nm was used as a light source for the ablation. A nitrogen ion beam with energies in a range of 200–800 eV is used to assist the deposition. The nitrogen ion implantation can compensate the possible loss of nitrogen species in the ablated plasma and can effectively assist the deposition by providing energetic nitrogen ions. Raman and Fourier transform infrared spectroscopy measurements were used to characterize the deposited thin films. The influences of the substrate temperature and the ion energy on the electronic and structural properties of the deposited thin films were studied.

The dependence of the time decay of magnetization on orientation ratio was investigated for longitudinal Co–alloy thin film media. The coercivity orientation ratio was controlled by the degree of mechanical texture. For oriented samples, it was found that the remanent magnetization along the circumferential direction decayed faster with time than that along the radial direction when the applied reverse magnetic field was near the remanent coercivity. However, the remanent magnetization along the circumferential direction decayed more slowly with time than that along the radial direction when the applied reverse magnetic field was less than roughly half the remanent coercivity. Anisotropic interactions and magnetic anisotropy distributions appear to be the cause for the different time decay of magnetization along the circumferential and radial directions for oriented media.

Fine equiaxed γ‐CoxFe2−xO3 (x=0, 0.06) particles with a diameter ranging from 200 to 1000 A were prepared by chemical precipitation. The average crystallite sizes were determined from x‐ray line broadening measurements. The saturation magnetization and magnetocrystalline anisotropy of the particles were determined by using the approach to saturation. An empirical linear dependence of the specific saturation magnetization σs on the specific surface area Sa of the fine crystallites was obtained in the form of σs(S)=σs(∞)(1−ASa). The slope A which reflects the surface spin canting anomaly is different for γ‐Fe2O3 and γ‐Co0.06Fe1.94O3 particles. Under the supposition of the fine crystallite consisting of two parts, i.e., the surface layer, whose magnetic moment cannot be turned entirely along the direction of the applied field, but makes an average canting angle with the field, and the inner part, whose magnetic moment can be aligned along the direction of the applied field, the above formula can be interpret...