Search

We investigated interlayer exchange coupling through Pt/Ru/Pt and Pt/Ru multilayers as candidates of nonmagnetic spacer layers in the synthetic antiferromagnetic (AF) layer, which is available for studying AF spintronics using current-induced spin–orbit torque (SOT) switching originating from the spin Hall effect. The AF interlayer exchange coupling with the oscillation period of Λ2 ∼ 1.05 nm was observed even for the face-centered cubic (fcc) Pt (tPt)/hexagonal Ru/fcc Pt (tPt) nonmagnetic spacer layer structures in the wide range of both Pt and total nonmagnetic spacer layer thicknesses (0 ≤ tPt ≤ 0.8 nm, 1.0 ≤ ttotal ≤ 2.3 nm), which would be useful for the systematic investigation of the SOT on the AF structure. Moreover, we observed the disappearance of the one oscillation period (Λ1 ∼ 1.65 nm) in the case of Pt(111)/Ru(0001) and Pt(111)/Ru(0001)/Pt(111) spacer layers, whereas the existence of two oscillation periods of AF interlayer exchange coupling (Λ1 ∼ 1.65 nm and Λ2 ∼ 1.05 nm) in the case of Ru spacer layer was observed. We expect that the Pt/Ru/Pt spacer layer with the oscillation period of Λ2 ∼ 1.05 nm will pave a way to the AF spintronics based on the multilayer systems. [ABSTRACT FROM AUTHOR]

We investigated an effect of sputtering gas species Ar, Kr, and Xe for deposition of a W insertion layer W(Ar, Kr, and Xe) in the synthetic ferrimagnetic reference layer consisting of [Co/Pt] multilayer/Ru/[Co/Pt] multilayer/W/CoFeB on magnetic properties of the reference layer and tunnel magnetoresistance ratio (TMR ratio) of magnetic tunnel junction (MTJ) stacks with the reference layer. In all the cases, the TMR ratio increased with the increase of the W insertion layer thickness $t_{\mathrm {W}}$ and showed a maximum at certain $t_{W}$. Although the maximum TMR ratio is almost the same for all the cases, $t_{\mathrm {W}}$ range in which we observed the maximum TMR ratio is dependent on the gas species; $t_{W} = 0.2$ nm for Ar, $t_{\mathrm {W}} = 0.2$ –0.4 nm for Kr, and $t_{\mathrm {W}} = 0.2$ –0.5 nm for Xe, indicating that $t_{\mathrm {W}}$ margin giving high-TMR ratio becomes wider with increasing atomic number of the gas species. The lower TMR ratio for W (Ar) at larger $t_{\mathrm {W}}$ region is due to the degradation of ferromagnetic coupling between the CoFeB and Co/Pt multilayer sandwiching W, resulting in canting of magnetization in the CoFeB layer. We found that an intermixing of Pt atoms in the Co/Pt multilayer occurred in the MTJ stack with W (Ar), whereas it did not intermix with W (Kr), indicating that the Pt interdiffusion caused the degradation of ferromagnetic coupling through W layer. [ABSTRACT FROM AUTHOR]

We investigated magnetic anisotropy and tunnel magnetoresistance (TMR) properties in MgO/(Co0.25Fe0.75)100-xBx stack structures with x=0, 15, 20, and 25 (in at.%). After annealing at 350 ^\circC, the easy axis of magnetization switches from in-plane to perpendicular direction in 1.5-nm-thick CoFeB with the B composition near x=15. The effective magnetic anisotropy energy density (Keff) shows a maximum of 1.9\times 10^5\ J/m^3 in the 1.5 nm-thick CoFeB film with x=20 annealed at 350 ^\circC. Keffis determined by the competition between contributions of interface anisotropy energy per effective CoFeB thickness (Ki/t^\ast, where t^\ast is the effective CoFeB layer thickness) and demagnetization energy (-MS^2/2\mu0). Bulk magnetic anisotropy energy (Kb) is negligibly small with comparison to those two terms. To obtain MgO/ferromagnetic stack structure with a high Keff, materials and structures that reduce demagnetization energy while maintaining a high Ki and a thin t^\ast have to be explored. In MTJs with the higher B compositions, high TMR ratio is obtained at higher annealing temperature. High TMR ratio of 136% is observed in a MTJ with x=25 annealed at 350 ^\circC. [ABSTRACT FROM AUTHOR]

We investigated tunnel magnetoresistance (TMR) properties in double MgO-barrier magnetic tunnel junctions (DMTJs) with (Co25Fe75)100-xBx free-layers with x= 15, 20, and 25 (in at.%) sputtered at different power. The TMR ratio of DMTJs increased with sputtering power, which is ascribed to the B composition reduction in the CoFeB free-layer with increasing sputtering power. The x-ray diffraction measurement showed that crystallization into (001)-oriented texture of CoFeB film sandwiched between the two MgO-layers as well as an improvement of (001) orientation of top MgO-barrier are realized. The TMR ratio over 200% was obtained in DMTJs with a (Co25Fe75)85B15 free-layer sputtered at 0.88 and 1.77 W/cm^2. [ABSTRACT FROM AUTHOR]

We studied the magnetic and magnetoresistance characteristics of pseudospin-valve magnetic tunnel junctions (MTJs) based on CoFe/Pd multilayer electrodes with perpendicular magnetic anisotropy and an MgO barrier. The MTJs at annealing temperature (Ta) of 473 K showed a tunnel-magnetoresistance (TMR) ratio of 1.5%. An fcc (111)-oriented texture of the bottom and top Co90Fe10 /Pd multilayer electrodes, together with an imperfectly crystallized MgO, were revealed by cross-sectional TEM images. The TMR properties of perpendicular MTJs with a Co20Fe60B20 or Co50Fe50 layer inserted between the CoFe/Pd multilayer electrodes and the MgO barrier were also studied. The TMR ratio with Co20Fe60B20 insertion was L7% at Ta = 473 K and monotonically decreased at Ta over 523 K. The TMR ratio with Co50Fe50 insertion increased up to 3% at Ta = 573 K and then decreased to 0.4% at Ta = 598 K. The influence of the Pd layer on CoFeB was studied by using the simplified structures of Pd/CoFeB/MgO/CoFeB/Pd and Ta/CoFeB/MgO/CoFeB/Ta with inplane anisotropy. A former structure with Pd resulted in reduced TMR ratio which decreases with increasing Ta, whereas MTJs with a Ta-based structure showed a monotonic increase of a TMR ratio. The low TMR ratio observed in Pd-containing structures appears to result from crystallization of CoFeB in an unfavorable crystal orientation. [ABSTRACT FROM AUTHOR]

We investigated the effect of using a synthetic ferrimagnetic (SyF) free layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced magnetization switching (CIMS), particularly for application to spin-transfer torque random access memory (SPRAM). The employed SyF free layer had a Co40Fe40B20/Ru/Co40Fe40B20 and Co20Fe60B20/Ru/Co20Fe60B20structures, and the MTJs (100 × (150-300) nm²) were annealed at 300 °C. The use of SyF free layer resulted in low intrinsic critical current density (Jc0) without degrading the thermal-stability factor (E/kB T, where E, kB, and Tare the energy potential, the Boltzmann constant, and temperature, respectively). When the two CoFeB layers of a strongly antiferromagnetically coupled SyF free layer had the same thickness, Jc0) was reduced to 2-4 × 106 A/cm². This low Jc0) may be due to the decreased effective volume under the large spin accumulation at the CoFeB/Ru. The E/kBT was over 60, resulting in a retention time of over ten years and suppression of the write current dispersion for SPRAM. The use of the SyF free layer also resulted in a bistable (parallel/antiparallel) magnetization configuration at zero field, enabling the realization of CIMS without the need to apply external fields to compensate for the offset field. [ABSTRACT FROM AUTHOR]

In this paper, recent developments in magnetic tunnel junctions (MTJs) are reported with their potential impacts on integrated circuits. MTJs consist of two metal ferromagnets separated by a thin insulator and exhibit two resistances, low (Rp) or high (RAP), depending on the relative direction of ferromagnet magnetizations, parallel (P) or antiparallel (AP), respectively. Tunnel magnetoresistance (TMR) ratios, defined as (RAP - Rp)/Rp as high as 361%, have been obtained in MTJs with Co40Fe40B20 fixed and free layers made by sputtering with an industry-standard exchange-bias structure and postdeposition annealing at Tα = 400 °C. The corresponding output voltage swing ΔV is over 500 mV, which is five times greater than that of the conventional amorphous Al-O-barrier MTJ5. The highest TMR ratio obtained so far is 500% in a pseudospin-valve MTJ annealed at Tα = 475 °C, showing a high potential of the current material system. In addition to this high-output voltage swing, current-induced magnetization switching (CIMS) takes place at the critical current densities (Jco) on the order of 106 A/cm² in these MgO-barrier MTJs. Furthermore, high antiferromagnetic coupling between the two CoFeB layers in a synthetic ferrimagnelic free layer has been shown to result in a high thermal-stability factor with a reduced Jco compared to single free-layer MTJ5. The high TMR ratio enabled by the MgO-barrier MTJs, together with the demonstration of CIMS at a low Jco, allows development of not only scalable magnetoresistive random-access memory with feature sizes below 90 nm but also new memory-in-logic CMOS circuits that can overcome a number of bottlenecks in the current integrated-circuit architecture. [ABSTRACT FROM AUTHOR]

The first example of dual inhibitors for matrix metalloproteinase (MMP) and cathepsin is described. An appropriate alignment of peptide-parts and two different specific functional groups in one molecule led to the discovery of a potent dual inhibitor (3a). [Copyright &y& Elsevier]

Abstract: We investigated the relationship between the tunnel magnetoresistance (TMR) ratio and the electrode structure in MgO-barrier magnetic tunnel junctions (MTJs). The TMR ratio in an MTJ with Co40Fe40B20 reference and free layers reached 355% at the post-deposition annealing temperature of T a=400°C. When Co50Fe50 or Co90Fe10 is used for the reference layer material, no high TMR ratio was observed. The key to have high TMR ratio is to have highly oriented (001) MgO barrier/CoFeB crystalline electrodes. The highest TMR ratio obtained so far is 450% at T a=450°C in a pseudo-spin-valve MTJ. [Copyright &y& Elsevier]

Provides information on a study which examined the magnetic properties and microstructure of thin films with iron, nitrogen, aluminum and oxygen alloys. Details on saturated magnetization; Process of reactive sputtering; Methodology; Results and discussion.

We investigated spin-Hall effect (SHE) and degree of MgO (100) orientation in artificially synthesized (W/Hf)-multilayer/CoFeB/MgO systems with various W thicknesses. We found that the artificially synthesized multilayer systems can enhance the spin-Hall effect and control the value of spin diffusion length. We observed a maximum magnitude in both spin-Hall angle and spin-Hall conductivity as a function of W thickness in W/Hf-multilayer systems, and found that the values of spin-Hall conductivity are larger than that for β-phase W. In addition, a more highly oriented MgO (100) texture on CoFeB is obtained for (W/Hf)-multilayer systems prepared under low-Ar-pressure condition, which would be suitable for preparation of magnetic tunnel junctions with high tunnel magnetoresistance properties on (W/Hf)-multilayer heavy metal electrode. These results suggest that the artificially synthesized multilayer system is one of the avenues for realizing spin devices using spin-orbit torque. [ABSTRACT FROM AUTHOR]

The influence of magnetic damages at the sidewall of perpendicular magnetic tunnel junctions (p-MTJs), which are the core devices of spin-transfer-torque magnetoresistive random-access memory (STT-MRAM), is discussed based on the thermal stability factor, Δ, double-logarithmic plot of normalized switching energy barrier, E, and saturation magnetization, Ms, and their exponential slope, n. Δ was calculated using the string method under the simulation conditions of domain wall motion switching. n increased with the increasing thickness of the damaged layer of the sidewall. Notably, the sidewall damage can be explained by the reduction in Ms and exchange stiffness constant, As, rather than the interfacial perpendicular anisotropy. The findings of this study are important for controlling and improving the process damage in the mass production of p-MTJs in STT-MRAM. [ABSTRACT FROM AUTHOR]

We studied the spin-Hall effect and perpendicular magnetic anisotropy in W/Hf multilayer/CoFeB/MgO and W80Ta20/Hf multilayer/CoFeB/MgO systems and compared them with those in the β-W/CoFeB/MgO system. From the cross-sectional high-resolution transmission electron microscopy images, (i) the amorphous structure of W/Hf and W80Ta20/Hf multilayers, (ii) the flat interface between heavy metals and CoFeB, and (iii) highly (100) texture of MgO (1.0 nm) on CoFeB were observed in those multilayer systems. A higher spin-Hall effect and enhancement of perpendicular magnetic anisotropy in the W/Hf multilayer/CoFeB/MgO system can be achieved compared to the β-W/CoFeB/MgO system. In addition, we found that the resistivity in amorphous W/Hf multilayers is low compared to that in β-W. These results suggest that the artificially synthesized multilayer system is one of the avenues for realizing the heavy metal with a large spin-Hall effect and low resistivity. [ABSTRACT FROM AUTHOR]

We studied spin Hall effect (SHE) in Pt100-xAux with various Au compositions x for Pt-Au/CoFeB systems by means of spin Hall magnetoresistance (SMR). We synthesized low resistive, flat, and highly (111)-textured Pt-Au alloy films by sputtering using low pressure Kr gas. We found that spin Hall angle (θSH), spin Hall conductivity (σSH), and spin diffusion length (λS) increase by alloying Pt with Au at certain x. The enhancement of σSH is consistent with the theoretically predicted increase in the intrinsic spin Hall conductivity, however quantitatively, there are some discrepancies in θSH and λS between our result and the experimental and theoretical results in the literatures 19 and 20. The discrepancy between our results and previous results would be related to the difference of the nanostructure in Pt-Au alloys related to the scattering from film surfaces and grain boundaries and the degree of phase separation in Pt-Au alloy systems. [ABSTRACT FROM AUTHOR]

The influence of the sidewall damage on the thermal stability factor (Δ) of quad-interface magnetic tunnel junctions (quad-MTJs) was investigated through a string method-based micromagnetic simulation. The quad-MTJs consist of a reference layer/MgO-barrier/CoFeB/middle-MgO/CoFeB/MgO-cap, which has four CoFeB/MgO interfaces to enhance the interfacial perpendicular magnetic anisotropy for large Δ. Experimentally obtained magnetic parameters at room temperature [e.g., saturation magnetization (Ms), stiffness constant (As), interfacial perpendicular magnetic anisotropy constants (Ki), and exchange coupling (Jex)] in blanket multilayer films of the quad-MTJs were used in micromagnetic simulation. The influence of the sidewall damage on the quad-MTJs, which is difficult to be analyzed in the experimental way, was investigated. The quad-MTJs without damaged layers having relatively higher Ki show the split of the energy barrier into two, resulting in a decrease in Δ. When the decrease in magnetic anisotropy energy (Eani) is more than the increase in the static magnetic energy (Esta), the antiferromagnetically (AF) coupled state of two free layers is formed at the midpoint to minimize the total energy (Eall). This causes the split of the energy barrier. The sidewall damage plays a role in lowering Ki in each layer, consequently avoiding the formation of the AF state. Note that the value of Δ with the sidewall damage, which shows the unified energy barrier, is comparable to non-damaged Δ, which shows the split of the energy barrier; these quad-MTJs have the same volume of free layers. [ABSTRACT FROM AUTHOR]

This paper reports the relationship between the heat treatments of the CoFeB/MgO/CoFeB/Ta-based magnetic tunnel junction (MTJ) and the chemical bonding state using angle-resolved hard X-ray photoelectron spectroscopy. The redox reaction for B 1s during postannealing was verified for the MTJ without a capping layer by oxidizing the metallic B 1s in CoFeB and reducing the oxidized Fe 2p and Co 2p near the surface. For the MTJ with a capping layer, regardless of the heat treatments, MgO was found to be in a peroxidized state, and the diffusion of O 1s and B 1s exerted by the heat treatments is considered to be controlled by the degree of crystallization of MgO. The composition at the MgO/CoFeB interface changes on account of the heat treatments since the ratio of CoFeB and TaB at the bottom changes as a result of boron diffusion through the grain boundaries in MgO. By postannealing at 400 °C, the peak binding energy of Mg 1s at the surface was found to shift slightly to lower energy toward the stoichiometric MgO. However, the release of the excess oxygen in MgO is suppressed by the crystallization. Since the crystallization of MgO is enhanced by the in situ IR heating, the internal oxygen is more constrained in MgO. An improvement of the tunneling magnetoresistance deterioration observed with an ultrathin MgO is considered to be achieved under the peroxidized state controlled by the crystallinity of MgO. [ABSTRACT FROM AUTHOR]

Current-induced magnetic domain wall (DW)-motion device with a three- or four-terminal structure has considerable potential to trigger a profound transformation in memory and logic technologies. In this paper, we give an overview of DW-motion devices and describe their structure, operation method, and characteristics. Previous studies on the DW motion in nanowires with a Co/Ni multilayer are also reviewed. We also report on the experimental results regarding device properties, such as critical current, the time and energy required to displace the DW in the device, and retention properties with various device sizes down to 20 nm. The results reveal that writing properties are enhanced while sufficient retention properties are maintained as the device size is reduced, indicating that the DW-motion device has high scalability and compatibility with conventional semiconductor-based cells as well as ultralow power capability. [ABSTRACT FROM AUTHOR]

The material development of magnetic tunnel junction with a perpendicular easy axis is in great demand to advance spin-transfer torque magnetoresistive random access memory (STT-MRAM) technologies. To realize high-speed and high-density STT-MRAM, a thin-film magnetic material with large perpendicular anisotropy and small spontaneous magnetization has great potential. Here, we develop a thin-film deposition technique for a-few-nanometer-thin L10-MnAl by sputtering and investigate its structure and magnetic properties. Utilization of the B2-CoAl buffer layer allows us to grow L10-MnAl with a large crystalline anisotropy of 8.5 × 105 J/m3, the small spontaneous magnetization of 0.62 T, and the tolerance for 400 °C annealing even at the MnAl thickness of 2 nm. We calculate the device properties based on the obtained material parameters and find that high retention properties, high-speed switching, and low write-error rate can be obtained at the single-digit-nm region, which are not readily achieved by conventional material systems. The results show the potential of L10-MnAl for high-density and high-speed STT-MRAM. [ABSTRACT FROM AUTHOR]

Junction size (D) dependence of thermal stability factor (\mit\Delta) and intrinsic critical current (IC0) were investigated for MgO/CoFeB/Ta/CoFeB/MgO recording structure in magnetic tunnel junctions (MTJs) having a CoFeB reference layer and a synthetic ferrimagnetic (SyF) reference layer. \mit\Delta of the recording structure shows almost constant value down to 40 nm, whereas IC0 shows a linear dependence on the recording layer area, as similarly observed in recording structure with single-interface. Average absolute intrinsic critical current density is 3.5 MA/cm^2, which is comparable to previously reported value for recording structure with single-interface. A MgO/CoFeB(1.4)/Ta(0.4)/CoFeB(1.0)/MgO double-interface recording structure in MTJ with SyF reference layer shows \mit\Delta of 59 at D=29\ nm. [ABSTRACT FROM AUTHOR]

The development of STT-MRAM technology is currently in progress and has been successively disclosed by major LSI vendors recently. In order to advance STT-MRAM technology and expand its areas of application, challenges relative to further device scaling need to be addressed. In this study, an increased wiring resistance in a deep sub-100 nm process by which the read operation yield is degraded was analyzed. The yield degradation was quantified by analyzing the conventional cell array using Monte-Carlo SPICE simulations. A new circuit was proposed to decrease the fail bit rate by an averaged reference voltage ($V_{\mathrm {ref}}$) generator. The simulated results indicated that the new $V_{\mathrm {ref}}$ generator improved the fail bit rate by 1 order of magnitude compared to the conventional array. To demonstrate the circuit operation, a 128 Mb STT-MRAM chip was designed and fabricated using 40 nm CMOS and 37 nm MTJ technologies. For the first time, the chip measurements successfully demonstrated the operation of the proposed device-variation tolerant array architecture with the averaged $V_{\mathrm {ref}}$ generator, presenting a 30 ns read access time. [ABSTRACT FROM AUTHOR]

We investigate switching probabilities of electric field-induced magnetization switching in CoFeB/MgO based magnetic tunnel junction with perpendicular magnetic easy axis under static magnetic field with various directions. The switching takes place through magnetization precession with the period determined by the magnitude of the in-plane component of magnetic field. The experimental results are well reproduced by macro-spin simulation. The simulation reveals that decoherence induced by thermal fluctuations and/or other effects limit the switching probabilities in the present system. [ABSTRACT FROM PUBLISHER]

We fabricated a quadruple-interface perpendicular magnetic tunnel junction (MTJ) (Quad-MTJ) down to 33 nm using physical vapor-deposition, reactive ion etching, and damage-control integration process technologies that we developed under a 300-mm process. We demonstrated the greater scalability and higher writing speed of Quad-MTJ compared with double-interface perpendicular MTJ: 1) it has twice the thermal stability factor—1X nm Quad-MTJ can achieve 10 years retention—while maintaining a low resistance-area product and high tunnel magnetoresistance ratio; 2) smaller overdrive ratio of write voltage to obtain a sufficiently low write-error rate; 2) smaller pulsewidth dependence of the switching current; and 4) more than double the write efficiency at 10-ns write operation down to 33-nm MTJ. The effective suppression of the switching current increase for higher write speeds was explained by the spin-transfer-torque model using the Fokker-Planck equation. Our 33-nm Quad-MTJ also achieved excellent endurance (at least 1011) owing to its higher write efficiency and low-damage integration-process technology. It is thus a promising method for low power, high speed, and reliable STT-MRAM with excellent scalability down to the 1X nm node. [ABSTRACT FROM AUTHOR]

We propose a novel method to evaluate the accurate thermal stability factor \Delta 0 quickly, in 10 min for one target magnetic tunnel junction (MTJ), without magnetoresistance random access memory chip which includes CMOS devices. This method is based on the thermal disturbance between parallel state and antiparallel state at high temperature as well as the temperature dependence of material properties. Using this method, we have successfully demonstrated that \Delta 0 factors of 70 nm $\phi $ p-MTJ with single and double CoFeB/MgO interfaces at 24 °C are 76.1 and 178.2, respectively. The value of \Delta 0 of p-MTJ with double CoFeB/MgO interface is about twice as single one. [ABSTRACT FROM AUTHOR]

Monoethanolamine (MEA), a toxic organic chemical, is widely used in industries and is found in their wastewater. Anaerobic MEA degradation is an appropriate strategy to reduce energy and cost for treatment. Industry wastewaters also contain sulfate, but information on the effects of sulfate on MEA degradation is limited. Here, an up-flow anaerobic sludge blanket (UASB) for MEA-containing wastewater treatment was operated under psychrophilic conditions (18–20 ºC) to investigate the effects of sulfate on the microbial characteristics of the retained sludge. To acclimatize the sludge, the proportion of MEA in the influent (containing sucrose, acetate, and propionate) was increased from 15% to 100% of total COD (1500 mg L–1); sulfate was then added to the influent. The COD removal efficiency remained above 95% despite the increase in MEA and sulfate. However, granular sludge disintegration was observed when sulfate was increased from 20 to 330 mg L–1. Batch tests revealed that propionate and acetate were produced as the metabolites of MEA degradation. In response to sulfate acclimation, methane-producing activities for propionate and hydrogen declined, while sulfate-reducing activities for MEA, propionate, and hydrogen increased. Accordingly, acclimation and changes in dominant microbial groups promoted the acetogenic reaction of propionate by sulfate reduction. [Display omitted] • Monoethanolamine (MEA) was satisfactorily removed by UASB treatment. • Increasing sulfate levels in wastewater caused deterioration of the retained sludge. • Propionate and acetate were detected as anaerobic degradation products of MEA. • Microbial community structure was markedly changed by increasing MEA and sulfate. [ABSTRACT FROM AUTHOR]

A non-volatile memory element called a perpendicular-anisotropy magnetic tunnel junction was fabricated using CoFeB/MgO/CoFeB film stack technology. It exhibits two stable resistance values, high or low, depending on the relative directions of the magnetizations of the two ferromagnetic CoFeB layers. After being programmed into the high resistance state with a current injection scheme based on the spin transfer torque theory, the tunnel junction was exposed to 15-MeV Si ions under different voltage stress conditions. The tested structure remained in the programmed high resistance state after being bombarded with 10–100 Si ions, even under the stressed situations. A time-domain analysis proved that this result is due to the perfect immunity of the tested magnetic tunnel junction to single event upsets. Some degradation in resistance due to the heavy-ion irradiation was detected through a precise parameter analysis based on a tunneling theory but it was negligibly small (1%). There were no statistically significant changes in the thermal stability factor before and after irradiation, and this means the long-term retention properties remained unchanged. [ABSTRACT FROM PUBLISHER]

We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic heterostructures are strongly influenced by doping the Ta underlayer with nitrogen. In particular, the saturation magnetization drops upon doping the Ta underlayer, suggesting that the doped underlayer acts as a boron diffusion barrier. In addition, the thickness of the magnetic dead layer decreases with increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy increases to ∼1.8 erg/cm2 when an optimum amount of nitrogen is introduced into the Ta underlayer. These results show that nitrogen doped Ta serves as a good underlayer for spintronic applications including magnetic tunnel junctions and domain wall devices. [ABSTRACT FROM AUTHOR]

We show a three terminal magnetic tunnel junction (MTJ) with a 10-nm thick channel based on an interconnection material Cu with 10% Ir doping. By applying a current density of less than 1012 A m-2 to the channel, depending on the current direction, switching of a MTJ defined on the channel takes place. We show that spin transfer torque (STT) plays a critical role in determining the threshold current. By assuming the spin Hall effect in the channel being the source of the STT, the lower bound of magnitude of the spin Hall angle is evaluated to be 0.03. [ABSTRACT FROM AUTHOR]

We investigated the effect of a magnetic field along a hard in-plane axis Hhard on a current-induced magnetization switching (CIMS) in magnetic tunnel junctions (MTJs). Since Hhard causes the effective field to tilt away from the easy axis, we evaluated the Hhard dependence of two contributing factors in CIMS [the intrinsic critical current density (Jc0) and the thermal stability factor (E/kBT)] as functions of the tilting angle (θH). Both measurements and numerical simulations showed that the presence of Hhard can reduce Jc0 by more than the amount estimated by Slonczewski's polarization function g(θ) by an order of magnitude and that E/kBT is independent of θH. These findings suggest that the effect of Hhard mainly appears in the dynamic properties due to the nonconservative force of the spin-transfer torque based on the Slonczewski's model. A simple stability analysis demonstrated that the tilt of the magnetization direction away from the easy axis caused by the presence of Hhard induces an imbalance between the spin-transfer and damping torques and that applying a current achieves the further tilted stable state. Achievement of this stable state can be interpreted as the suppression of the effect of the effective demagnetization field (H*d). Therefore the major reduction in Jc0 is due to the suppression of H*d caused by the presence of Hhard. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of the fixation of the orientations of the two long chains, three types of novel derivatives of scavenger receptor inhibitor 1 were synthesized, and their biological activities were evaluated. Among the novel derivatives, 2,4-bis(octadecanoylamino)benzenesulfonic acid sodium salt (4d) showed the most potent inhibitory activity against the incorporation of 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate-labeled acetyl-LDL (DiI-acetyl-LDL) into macrophages. 2,5-Bis(octadecanoylamino)benzenesulfonic acid sodium salt (4c), a regioisomer of 4d, did not exhibit as potent an inhibitory activity as 4d, meaning that the substitution pattern of two long chains on the benzene ring must be important. Compound 4d exhibited 10 times more potent inhibitory activity against the binding of 125I-labeled acetyl-LDL to the surface of macrophages than compound 1. [Copyright &y& Elsevier]

Scavenger receptors have been proven to be implicated in the formation of atherosclerotic lesions. A series of novel derivatives of sulfatides were synthesized, and their inhibitory activities against incorporation of DiI-acetyl-LDL into macrophages were evaluated in order to clarify the structure–activity relationships of sulfatides as a scavenger receptor inhibitor and find out novel inhibitors with synthetic easiness. The chemical modification of the substructures of sulfatides led to the establishment of the following structure–activity relationships; (1) the ceramide moiety can be replaced with another structure bearing two long chains, (2) the galactose moiety can be replaced with another structure or be deleted without a large decrease in the inhibitory activity, (3) the sulfate moiety was crucial, and it was the most preferable functional group for a potent inhibitory activity. The inhibitory activity of (S)-2-octadecanoylamino-2-tetradecylcarbamoyl)ethyl sulfate sodium salt (3a) against incorporation of DiI-acetyl-LDL into macrophages was proven to be based on the inhibition against the binding of acetyl-LDL to the surface of macrophages. We discovered novel scavenger receptor inhibitors with synthetic easiness, such as (S)-2-octadecanoylamino-2-(tetradecylcarbamoyl)ethyl sulfate sodium salt (3a) and 2-octadecanoylamino-1-(octadecanoylaminomethyl)ethyl sulfate sodium salt (13q). [Copyright &y& Elsevier]

We examined the effect of a hydroxamic acid-based matrix metalloproteinase inhibitor (KB-R7785), which we previously demonstrated to have a potent ameliorating effect on acute graft-versus-host disease (GVHD), and on the graft-versus-leukaemia (GVL) effect of allogeneic bone marrow transplantation (BMT). KB-R7785 was administered to (C57BL/6 × BALB/c) F1 (CBF1) mice that had been inoculated with IgE-producing B53 hybridoma cells of BALB/c origin as a model tumour, along with or without transplantation of C57BL/6 (B6) bone marrow cells and spleen cells (BMS). Administration of KB-R7785 without BMS significantly prolonged the survival of B53-inoculated CBF1 mice by inhibiting the infiltration of B53 cells into the liver and spleen. Transplantation of B6 BMS without KB-R7785 resulted in the death of most recipients due to acute GVHD while efficiently eliminating B53 cells. Administration of KB-R7785 along with B6 BMS resulted in a 50% survival of B53-inoculated CBF1 mice over 50 d without histological manifestations of acute GVHD or residual B53 cells. These results indicate the beneficial effects of KB-R7785 that inhibit tumour infiltration and prevent acute GVHD while preserving the GVL effect of allogeneic BMT. [ABSTRACT FROM AUTHOR]

This work reports on hard x-ray photoelectron spectroscopy (HAXPES) of CoFeB based tunnel junctions. Aim is to explain the role of the boron diffusion for the observed improvement of the tunneling magnetoresistance ratio with increasing annealing temperature. The high bulk sensitivity of HAXPES was used as a nondestructive technique to analyze CoFeB–MgO–CoFeB magnetic tunnel junctions. The investigated samples were processed at different annealing temperatures from 523 to 923 K. Hard x-ray core level spectroscopy reveals an enforced diffusion of boron from the CoFeB into the adjacent Ta layer with increasing annealing temperature. The dependence of the tunneling magnetoresistance on the annealing temperature is explained by the combined effects of an improved crystalline structure together with a change in the spin polarization at the Fermi energy caused by the removal of boron from the CoFeB layer and Ta diffusion at high annealing temperature. [ABSTRACT FROM AUTHOR]

The structure of a magnetic tunnel junction (MTJ) patterned by reactive ion etching is investigated in detail. Using a scanning transmission electron microscope (STEM) and energy-dispersive X-ray spectroscopy (EDX) combined with electron beam tomography, the unknown 3D interface roughness of CoFeB/MgO/CoFeB was successfully observed. From the orthoslice image, the interface morphology revealed characteristic features influenced by the roughness of the underlying layer. In contrast, a uniform morphology was observed for the metal layers except for the oxidized outer periphery of the MTJ. Additionally, we demonstrate that redeposited material at every turn of the MTJ side wall during the MTJ etching can be observed three-dimensionally by identifying the constituent elements using an electron tomographic technique combined with EDX. This analysis demonstrates a promising method to clarify the cause of electrical shorting of the ultra-thin tunnel barrier in MTJs, the location of which is challenging to determine using conventional cross-sectional transmission electron microscopy (TEM). [ABSTRACT FROM AUTHOR]

Polycrystalline metal oxides find diverse applications in areas such as nanoelectronics, photovoltaics and catalysis. Although grain boundary defects are ubiquitous their structure and electronic properties are very poorly understood since it is extremely challenging to probe the structure of buried interfaces directly. In this paper we combine novel plan-view high-resolution transmission electron microscopy and first principles calculations to provide atomic level understanding of the structure and properties of grain boundaries in the barrier layer of a magnetic tunnel junction. We show that the highly [001] textured MgO films contain numerous tilt grain boundaries. First principles calculations reveal how these grain boundaries are associated with locally reduced band gaps (by up to 3 eV). Using a simple model we show how shunting a proportion of the tunnelling current through grain boundaries imposes limits on the maximum magnetoresistance that can be achieved in devices. [ABSTRACT FROM AUTHOR]

We evaluate current-induced effective magnetic fields in perpendicularly magnetized Ta/CoFeB/MgO structures from the external magnetic field angle dependence of the Hall resistance. We confirm the presence of two components of effective fields. The dependence of their magnitudes on Ta thickness implies that both components are related to the spin current in Ta layer generated by the spin Hall effect. [ABSTRACT FROM AUTHOR]