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The miniaturization of computer facilities conditioned by the miniaturization of applied components makes them very sensitive to radioactive radiation. This is where neutron and electromagnetic radiation come to the fore. The reason for the particularly pronounced effects of this radiation is the fact that they do not interact with the Coulomb force, so they pass (leave) the reactor vessel unimpeded. This study examines the reliability of magnetic and semiconductor computer memories in the field of neutron and gamma radiation. This study experimental, and conducted under well-controlled conditions. The combined measurement uncertainty of the experimental procedure is less than 5 %. Sophisticated methods of mathematical statistics were used to process the stochastic results of measurements. [ABSTRACT FROM AUTHOR]

Corrosion can be very harmful to the service life and several properties of reinforced concrete structures. The metal magnetic memory (MMM) method, as a newly developed spontaneous magnetic flux leakage (SMFL) non-destructive testing (NDT) technique, is considered a potentially viable method for detecting corrosion damage in reinforced concrete members. To this end, in this paper, the indoor electrochemical method was employed to accelerate the corrosion of outsourced concrete specimens with different steel bar diameters, and the normal components Bz and its gradient of the SMFL fields on the specimen surfaces were investigated based on the metal magnetic memory (MMM) method. The experimental results showed that the SMFL experimental Bz curves are consistent with the analytical results of the theoretical model. Furthermore, the crest-to-trough behavior on the Bz signal curve and its zero-point gradient spacing can more accurately indicate the corroded area's extent. Then, a magnetic characteristic parameter W based on a large amount of experimental data was established to characterize the degree of corrosion of the steel bars. The magnetic characteristic parameter W is linearly related to the maximum cross-sectional area loss rate x of the corroded reinforcement. This paper will lay the foundation for future research on corrosion detection of reinforced concrete structures based on the MMM method and provide a feasible way for non-destructive detection of corrosion independent of the influence of reinforcement diameter and magnetization history. [ABSTRACT FROM AUTHOR]

Perpendicular magnetic anisotropy (PMA) in magnetic thin films with low coercivity is desirable for magnetic memory devices. It has been found that a (111)-oriented or textured Pt seed layer can enhance PMA and is, therefore, commonly utilized in spintronic structures. We grow (111)-oriented Pt epitaxial films via off-axis sputtering on various substrates and investigate the optimal substrate and orientation for high quality, epitaxial growth. Our results show that Pt(111) epitaxial films grow remarkably well on MgAl2O4(001) with an exceptionally narrow X-ray diffraction rocking curve. This high-quality seed layer is found to promote epitaxial growth of Pt/Co50Fe50/Pt trilayers with strong PMA comparable to many repeats of the magnetic multilayers reported previously. In addition, the Pt seed layer enhances the maximum thicknesses of Co50Fe50 that can still maintain PMA up to 1.07 nm. [ABSTRACT FROM AUTHOR]

Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM) is a memory which has bit cells made of magnetic tunnel junctions (MTJs), which comprise a storage switchable magnetic layer ("free layer") and, typically, one thin insulating barrier and one stable magnetic layer providing reference spin polarization for read and write operations ("reference layer"). STT-MRAM may compete with conventional dynamic and static RAM on technological nodes below 22 nm, if its switching current is reduced. This goal may be achieved for MTJ, which has two insulating barriers and reference layers. Building such a double-barrier MTJ, however, faces tremendous material challenges. In this work, a new double-barrier MTJ design with a switchable reference layer is introduced. We show that its efficiency is similar to its counterpart with stable reference layers, but it is much easier to be built. [ABSTRACT FROM AUTHOR]

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, crosssection 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 of the low temperature phase. This work demonstrates that continuous ultra-thin film MnBi can achieve large magnetocrystalline anisotropy and theoretical magnetization. We also show that film delamination causes a significant variation in the magnetic performance, and leads to a large surface roughness. [ABSTRACT FROM AUTHOR]

Ever since the first observation of all-optical switching of magnetization in the ferrimagnetic alloy GdFeCo using femtosecond laser pulses, there has been significant interest in exploiting this process for data-recording applications. In particular, the ultrafast speed of the magnetic reversal can enable the writing speeds associated with magnetic memory devices to be potentially pushed towards THz frequencies. This work reports the development of perpendicular magnetic tunnel junctions incorporating a stack of Tb/Co nanolayers whose magnetization can be all-optically controlled via helicity-independent single-shot switching. Toggling of the magnetization of the Tb/Co electrode was achieved using either 60 femtosecond-long or 5 picosecond-long laser pulses, with incident fluences down to 3.5 mJ/cm2, for Co-rich compositions of the stack either in isolation or coupled to a CoFeB-electrode/MgO-barrier tunnel-junction stack. Successful switching of the CoFeB-[Tb/Co] electrodes was obtained even after annealing at 250 °C. After integration of the [Tb/Co]-based electrodes within perpendicular magnetic tunnel junctions yielded a maximum tunneling magnetoresistance signal of 41% and RxA value of 150 Ωμm2 with current-in-plane measurements and ratios between 28% and 38% in nanopatterned pillars. These results represent a breakthrough for the development of perpendicular magnetic tunnel junctions controllable using single laser pulses, and offer a technologically-viable path towards the realization of hybrid spintronic-photonic systems featuring THz switching speeds. [ABSTRACT FROM AUTHOR]

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Resonances are observed in the transmission between two coplanar waveguides coupled by ferromagnetic Co90Ta5Zr5 tubes that wrap around their shorted ends. The resonances are assigned to the magnetostatic surface waves that counter propagate along the tube perimeter. We use a model based on an infinite ferromagnetic tube, with elliptical cross section of roughly the same dimensions as the studied structure. Additional theoretical analysis of the fundamental precession mode observed in experiment is carried out. Periodic boundary conditions dictated by the tube perimeter and applied to magnetostatic surface waves quantitatively account for the experimentally observed bandwidth of excited modes, despite the contorted tubular shape. The tubular topology appears to be more important than the shape details. [ABSTRACT FROM AUTHOR]

We consider a uniformly magnetized particle (i.e., a macroscopic magnetic moment) with an easy axis anisotropy. The particle's moment is switched from 'up' to 'down' direction by an external magnetic field applied parallel to the easy axis and continuously swept from a positive to a negative value. In addition, a small constant perpendicular bias field is present. It is shown that while the driving field switches the particle's moment in a conventional damped way, the perpendicular field creates an admixture of the precessional (ballistic) switching that speeds up the switching process. Precessional contribution produces a non-monotonic dependence of the switching time on the field sweep time with a minimum at a particular sweep time value. We derive analytic expressions for the optimal point, and for the entire dependence of the switching time on the field sweep time. Our approximation is valid in a wide parameter range and can be used to engineer and optimize of the magnetic memory devices. [ABSTRACT FROM AUTHOR]

Nanostructures of ferromagnetic oxides having Curie temperatures above room temperature have potential for applications in memory devices and future spin-based electronic applications. In this article, we report on the dc and high frequency magnetic properties of arrays of elliptical CoFe2O4 nanopillars, covering a large area, fabricated by combined electron beam lithography, and a sol-gel based chemical route. The nanopillars were successfully fabricated on insulating oxidized silicon substrates and on epitaxial thin films of ferroelectric BiFeO3. We performed magnetic force microscopy and ferromagnetic resonance spectroscopy on the arrays to probe their magnetic properties. Due to the possible existence of dominant pinning sites, the CoFe2O4 nanopillars are not single-domain even at nanometer size scales. [ABSTRACT FROM AUTHOR]

Ge15Sb85 is a promising material for phase-change memory applications owing to its very short crystallization times. As deposited amorphous samples of sputter deposited Ge15Sb85 have been investigated by extended x-ray absorption fine structure (EXAFS) measurements on both, Sb and Ge K absorption edges. After crystallizing the specimen, x-ray diffraction (XRD) and EXAFS measurements have been performed to analyze the atomic structure at different annealing conditions. Thus, experimental techniques focusing on the long range order as well as on the local order have been combined. Sb atoms have on average 3.2(2) nearest neighbors, while Ge atoms have 4.0(3). The Ge–Ge and Ge–Sb bond lengths are determined to 2.46(2) and 2.66(1) Å, respectively and agree well with those observed in the amorphous phase of the common phase-change material Ge2Sb2Te5. After crystallizing the sample at 250 °C, very different EXAFS spectra with modified Ge–Sb bond lengths are observed. The higher concentration of Ge neighbors at the Ge edge as compared to the as-deposited sample is indicative for phase separation. For the corresponding sample, XRD does not show reflections of Ge, which indicates that the agglomeration of Ge is amorphous or below the coherence length of the x-radiation. The EXAFS spectrum shows a superposition of two phases: one with bond lengths which agree with sp3-hybridized Ge [2.43(1) Å] and another one with longer Ge–Ge bond lengths [2.79(8) Å]. This result can be explained by phase separation in the material. [ABSTRACT FROM AUTHOR]

Ge15Sb85 is a promising material for phase-change memory applications owing to its very short crystallization times. As deposited amorphous samples of sputter deposited Ge15Sb85 have been investigated by extended x-ray absorption fine structure (EXAFS) measurements on both, Sb and Ge K absorption edges. After crystallizing the specimen, x-ray diffraction (XRD) and EXAFS measurements have been performed to analyze the atomic structure at different annealing conditions. Thus, experimental techniques focusing on the long range order as well as on the local order have been combined. Sb atoms have on average 3.2(2) nearest neighbors, while Ge atoms have 4.0(3). The Ge–Ge and Ge–Sb bond lengths are determined to 2.46(2) and 2.66(1) Å, respectively and agree well with those observed in the amorphous phase of the common phase-change material Ge2Sb2Te5. After crystallizing the sample at 250 °C, very different EXAFS spectra with modified Ge–Sb bond lengths are observed. The higher concentration of Ge neighbors at the Ge edge as compared to the as-deposited sample is indicative for phase separation. For the corresponding sample, XRD does not show reflections of Ge, which indicates that the agglomeration of Ge is amorphous or below the coherence length of the x-radiation. The EXAFS spectrum shows a superposition of two phases: one with bond lengths which agree with sp3-hybridized Ge [2.43(1) Å] and another one with longer Ge–Ge bond lengths [2.79(8) Å]. This result can be explained by phase separation in the material. [ABSTRACT FROM AUTHOR]

This paper reports a formation process and electrical properties of a nonvolatile memory structure with atomic layer deposited Ru nanocrystals and a SiO2/Al2O3 bilayered tunnel barrier. Al2O3 tunnel barrier/Ru nanocrystals/Al2O3 blocking barrier were deposited sequentially on a SiO2 2 nm/Si substrate by an in situ atomic layer deposition (ALD) process. Ru nanocrystals grown on the Al2O3 surface for 80 ALD cycles had a spatial density of 2.4×1012 cm-2 and an average diameter of 2.6 nm (38% standard deviation in the diameter). Charging/discharging behavior of the Ru nanocrystals embedded in the metal-oxide-semiconductor capacitor structure was examined by programming/erase operations and comprehended in terms of asymmetric barrier height of the bilayered tunnel barrier. The memory structure showed charge retention of 91% and 85% after 105 s at room temperature and at 85 °C, respectively. [ABSTRACT FROM AUTHOR]

We have performed micromagnetic simulations to investigate the magnetic behavior of exchange spring grains for hard disk recording applications. The thickness ratio between magnetically hard and soft layers was varied while the soft layer anisotropy was altered to maintain a suitable energy barrier between opposite magnetization states. The minimum required magnetic field for switching a grain and the corresponding field angle were both significantly reduced in exchange spring material compared with single-phase grains. This could lead to reduced cross-track write errors in hard drive systems and assist the development of magnetic multilayer recording technologies. [ABSTRACT FROM AUTHOR]

The metal-oxide-semiconductor field-effect transistor (MOSFET) device containing silicon nanocrystals (nc-Si) is fabricated by an ion-beam technique. The parasitic effect in the subthreshold region is only observed by the application of high erasing pulses. By using the second derivative method, the formation of the parasitic transistor is confirmed. The parasitic transistor is only activated upon the trapping of holes into the nc-Si at the edge channel. In addition, electron or hole trapping in the nc-Si depend on the voltage polarity and magnitude, which lead to positive or negative shifts in the threshold voltage. This demonstrates the feasibility of memory applications in MOSFET device. [ABSTRACT FROM AUTHOR]

Both La0.375Pr0.25Ca0.375MnO3 (LPCMO) and La0.625Ca0.375MnO3 (LCMO) were found to exhibit coexistence of competing orders (phase separation) over a wide temperature range. However, substantial hysteretic behaviors in both of the temperature-dependent resistance [R(T)] and magnetization [M(T)] [also known as the persistent magnetic memory effect (PMME)] are only displayed in LPCMO. The results indicate that, in LPCMO, the size distribution of the coexisting charge-ordered insulating and metallic ferromagnetic (FM) phases plays a determinant role in the PMME effects in different temperature regimes. Moreover, due to the direct competition between the two coexisting phases, the system is most susceptible to the external applied field in the hysteretic temperature region. On the other hand, in LCMO, the phase transition between paramagnetic and FM is more like an isomorphic transition in pure materials, and thus does not show significant hysteresis. [ABSTRACT FROM AUTHOR]

The authors provided the formation and memory effects of nonvolatile multilayer nickel-silicide nanocrystal memory in this study. This proposed structure can efficiently improve the drawbacks of current floating gate and single-layer nanocrystal memories for the next-generation nonvolatile memory application. The charge trapping layer of multilayer structure was deposited by sputtering a commixed target (Ni0.3Si0.7) in the argon and nitrogen ambiance, and then used a low temperature rapid thermal annealing to form uniform nanocrystals. Transmission electron microscope images clearly show the multilayer and single-layer nanocrystal structures embedded in SiNx. X-ray photoelectron spectroscopy and x-ray diffraction also present the chemical states and crystallization of nanocrystals under different annealing temperature treatments. The capacitor with different memory structures was also studied and exhibited hysteresis characteristics after electrical operation. In addition, the multilayer nanocrystals revealed better charge storage ability and reliability than the single-layer nanocrystals. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions are prepared with Co-based Heusler compounds as one magnetic electrode and alumina as the tunnel barrier. The investigated compounds are Co2MnSi and Co2FeSi. An inversion of the tunnel magnetoresistance in the Co2FeSi as well as in the Co2MnSi case was found with alumina barriers at certain bias voltages at room and low temperatures. We present calculations of the density of states of these compounds based on fully relativistic spin-polarized KKR methods in order to elucidate the inversion. [ABSTRACT FROM AUTHOR]

We realized write-once-read-many-times (WORM) memory devices based on pentacene and demonstrated that the morphology control of the vacuum deposited pentacene thin film is greatly important for achieving the unique nonvolatile memory properties. The resulted memory devices show a high ON/OFF current ratio (104), long retention time (over 12 h), and good storage stability (over 240 h). The reduction of the barrier height caused by a large interface dipole and the damage of the interface dipole under a critical bias voltage have been used to explain the transition processes. The achievement of excellent WORM memory based on pentacene opens up a new application field for organic materials. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation of the thermal hysteresis of iron dots exchange-coupled to an antiferromagnetic substrate. We consider a temperature interval bounded by the Néel temperature of the substrate, and we calculate the heating and cooling curves in the presence of an external field oriented opposite to the interface exchange field. The thermal hysteresis is due to the temperature variation of the interface field and the influence of the geometrical shapes and sizes of the dots on the magnetic states and switching mechanisms. We show that Fe dots on an uncompensated NiO substrate exhibit large thermal hysteresis at room temperature, and external fields of a few kOe. The width of the hysteresis loops depends on the dimensions of the ferromagnetic dot, and can be significant for dots elongated in the direction of the interface field. [ABSTRACT FROM AUTHOR]

The hard magnetic L10 ordered phase formation in thin Pd and Fe bilayers prepared on MgO (001) substrate has been investigated by transmission electron microscopy using in situ annealing. The structures of as-deposited Fe/Pd and Pd/MgO interfaces were characterized by high-resolution transmission electron microscopy. Fast intermixing of Fe and Pd layers and immediate L10 phase formation within the alloyed area was found at 673 K. The high-resolution observations indicated that the ordered region of the L10-FePd phase was formed in dispersed areas without a predetermined nucleation site. At 773 K, the growing ordered areas occasionally formed antiphase boundaries between the adjacent parts. The ordered L10-FePd thin layer contained translational domains with tetragonal c axis perpendicular to the substrate. [ABSTRACT FROM AUTHOR]

The dependence of the exchange bias field and coercivity enhancement on ferromagnetic (FM) and antiferromagnetic (AF) layer thickness in exchange biased bilayers has been systematically investigated in CoFe/FeMn and CoFe/PdMn bilayers for digital encoding applications in biotechnology. A magnetic multilayer structure can be used as a digitally encoded tag if each (bi)layer has two magnetic states, positive and negative saturation, available at remanence and if each layer can be uniquely identified by its coercivity. We will demonstrate that by adjusting the AF and FM layer thickness in an AF/FM bilayer, both the bias field and the coercivity of the bilayer can be controlled. By contrasting CoFe/FeMn bilayers with CoFe/PdMn bilayers, it becomes apparent that the relative magnitudes of the coercivity enhancement and bias field depend on the particular AF material, although the qualitative behavior remains unchanged. In order to create a multilayer that can retain one of many magnetic states at remanence, a large coercivity enhancement but absent or small bias field are preferred. Analysis of the bilayers suggest that PdMn is a better choice of AF layer for this purpose and results on some multilayer films are shown which validate this claim. [ABSTRACT FROM AUTHOR]

Self-assembled FePt nanoparticle arrays are candidate structures for ultrahigh density magnetic storage media. One of the factors limiting their application to this technology is particle-to-particle compositional variation. This variation will affect the A1 to L10 transformation as well as the magnetic properties of the nanoparticles. In the present study, an analysis is provided for the formation mechanism of these nanoparticles when synthesized by the superhydride reduction method. Additionally, a comparison is provided of the composition distributions of nanoparticles synthesized by the thermal decomposition of Fe(CO)5 and the reduction of FeCl2 by superhydride. The latter process produced a much narrower composition distribution. A thermodynamic analysis of the mechanism is described in terms of free energy perturbation Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

The mechanism of lubricant migration on a flying slider’s air bearing surface in magnetic hard disk drives is examined in this paper. As the head-disk spacing diminishes, the lubricant contamination from the disk and its migration behavior on the flying head slider becomes an increasing concern. The spatiotemporal behavior of the thin lubricant film on a slider surface is complicated, and it is affected by many physical factors. We investigate the contributions and functionalities of the potentially related physical factors and parameters on the lubricant film dynamics by numerical simulation. The analysis results show that the air bearing shear stress is the primary driving force in the lubricant migration, while the air bearing pressure makes only a minor contribution. The relative strength and direction of the Couette and Poiseuille flow components of the air bearing shear stress govern the lubricant migration direction and the points of lubricant stagnation. The lubricant surface free energy plays an important role while the contribution of diffusion is relatively small through the Laplace pressure but relatively large through the lubricant disjoining pressure which is determined by the surface energy gradient. We also find that the lubricant viscosity affects the lubricant dynamics as a time scaling factor. These results reveal the underlying physical framework of the complex phenomena and provide useful insight for developing the head disk interface of magnetic disk drives. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to explore three-dimensional magnetic recording as a next generation recording technology. To defer the superparamagnetic limit in magnetic recording substantially beyond the 1 Tbit/in.2 mark, it is proposed to stack magnetic bits in a third (vertical) dimension. The vertical stacking underlies the concept of three-dimensional (3D) magnetic memory and recording—the primary subject of this paper. A clear distinction between absolute 3D memory and its trivial multilevel implementation is drawn. The paper focuses on the study of the media design and write and read processes. To minimize the intersymbol interference and improve stability, it is proposed to pattern the recording media in all three dimensions. Basic Co/Pd-based 3D recording media necessary for this study are fabricated using cosputter deposition. Focused-ion-beam-based fabrication is used to pattern the recording media into nanoscale bit cells. The physics of 3D magnetic recording is also investigated theoretically with Landau-Lifshits-Gilbert-based micromagnetic modeling. The ultimate goal of this paper is to help understand the physics of 3D and multilevel magnetic recordings and trigger wide interest in the studied concept. [ABSTRACT FROM AUTHOR]

A variety of magnetic memory devices, including MRAM, spin-torque RAM, plated wire, and bubbles, either are or have been under investigation as candidate “universal memory” devices. Such devices would combine the performance attributes of DRAM with the nonvolatility of a disk drive. This paper examines the past and present magnetic memories from two perspectives: (1) processing and extendability to smaller dimensions, and (2) the memory hierarchy of the applications to which they are directed. From a processing requirement, magnetic memories must converge to the cell sizes of competitive memory technologies, which range from 8F2 for DRAM to 0.5F2 for disk drives, where F is the minimum processing feature. From a memory hierarchy perspective, magnetic memories must balance the advantages of nonvolatility with the market demands for performance and low cost, and must address the application shifts away from classical enterprise storage hierarchy to the now rapidly developing mobile storage needs. The success of magnetic memories will depend on their ability to fulfill the evolving memory hierarchy requirements of a large set of new and nontraditional applications and on their ability to approach the device sizes of competing DRAM and flash devices. [ABSTRACT FROM AUTHOR]

This paper reports on the progress in perpendicular drive integration. In the first part, an experiment comparing the effect of magnetic spacing variation between longitudinal and perpendicular recordings is discussed. First, it is shown that the Wallace equation applies to perpendicular recording provided that the density of the recorded signal is sufficiently high. Using a thermal actuator, the effect of separately changing the read and write magnetic spacings of longitudinal and perpendicular head and media is compared. It is shown that the bit error rate is more sensitive to write space variations versus read space variations. However, the dependence is similar between longitudinal and perpendicular components. In the second part, two types of single-head, 95 mm, 7200 rpm desktop perpendicular drives (40 and 80 Gbyte capacity) are presented. They both achieve good bit error rate and off-track capability in all zones. The thermal decay rate of the 40 Gbyte drive was measured and compared to a similar longitudinal drive. It was found that the decay rate is much smaller in the case of the perpendicular drive in the range of -6–+80 °C. The thermal decay rate of the two perpendicular drives was compared at ambient temperature and found to be equally small. Finally, a measurement of the bit error rate of the 40 Gbyte perpendicular drive over the same temperature range demonstrates that the drive operates well in this temperature range. [ABSTRACT FROM AUTHOR]

The disjoining pressure of lubricant in the magnetic storage device head-disk interface (HDI) was obtained using Lifshitz theory [Sov. Phys. JETP 2, 73 (1956)] and multilayer film stack model. For this purpose the normal-air-gap-centered calculation of the disjoining pressure was replaced by the lubricant-layer-centered system. In the air-centered system the attractive force between the head and media was found to increase as the lubricant layer was thinned. By switching to the lubricant-centered system the disjoining pressure in a thin film of lubricant in the HDI was found to be negative at small head-to-media separation. By equating the free lubricant disjoining pressure with the lubricant in the head-disk interface, a thinning of the lubricant in the interface due to the presence of the head was calculated. A detailed thermodynamic analysis of the disjoining pressure of the lubricant in the interface revealed that the calculated negative disjoining pressure was due to the dominance of the air-gap-centered interaction energy for small air gaps. The impact on the lubricant film in the operating hard disk drive is discussed, and the possible role of negative disjoining pressure on the lubricant accumulation rate on the slider is highlighted. [ABSTRACT FROM AUTHOR]

We study the effective reversal times for bit-addressed precessional switching of the magnetization in magnetic random access memories (MRAMs). In our experiments the ultrafast magnetization dynamics of the free layer of a microscopic magnetic tunnel junction cell is accessed by means of ultrafast magnetotransport. Bit-addressed switching is studied by a fast perpendicular field pulse in combination with an easy axis bias field. For vanishing effective easy axis bias fields ultrafast quasiballistic switching of the magnetization can be achieved. Furthermore the characteristic oscillatory behavior of the precessional switching under variation of the pulse duration is observed. In a certain easy axis bias field range, the so-called addressing windows, the final magnetization state after the fast pulse is always aligned with the bias field which allows reliable bit addressing in a MRAM. Also here fast magnetization switching can be obtained. However, the decay time of the remaining magnetic excitations after bit addressing strongly depends on the initial and final orientations of the magnetization. This variation leads to different effective bit addressing times for switching and nonswitching events which could limit the MRAM operation speed. [ABSTRACT FROM AUTHOR]

We study the temperature dependence and low and high temperature limits of the magnetic shape memory effect (MSME) in five-layered tetragonal Ni–Mn–Ga martensite. Using a simple model we show that, additionally to the limits posed by transformation to austenite or an intermartensitic transformation, the temperature dependence of the magnetic anisotropy, tetragonality of the lattice, and twinning stress play important role when considering the temperature limits of the MSME. With decreasing temperature, the lattice distortion and magnetic anisotropy increase, but saturate in a low temperature region. The twinning stress does not saturate and its temperature dependence has exponential-like character that increases rapidly in the low temperature region. The model predicts that the low-temperature limit of the MSME is 165 K for Ni[sub 49.7]Mn[sub 29.1]Ga[sub 21.2] composition. This agrees very well with the value of 173 K determined from direct measurements. The high temperature limit is transformation to austenite at 315 K. The interval of the MSME existence is therefore 173–315 K. Quasistatic measurements of the MSME in the range 203–313 K up to the 1.15 T magnetic field show that the onset of the MSME shifts to a higher field and that a maximum field-induced strain increases with decreasing temperature. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Strong out-of-plane exchange biasing has been observed in out-of-plane exchange biased [Pt (5 Å)/Co (4Å)][SUB3]/NiO(11 Å multilayer with perpendicular easy axis. Both the exchange field H[SUBE] and coercivity H[SUBC] display a closely linear temperature dependence except at very low temperatures. A thin NiO layer coated on the top of a Pt/Co multilayer has a great effect on the domain pattern of the Pt/Co multilayer, which is in a more irregular configuration with much smaller domain sizes than the uncoupled Pt/Co multilayer. A simulation according to Malozemoff's random field model gives a good agreement to the experimental temperature dependence of H[SUBE] and H[SUBC], suggesting that the closely linear temperature dependences of H[SUBE] and H[SUBC] are strongly related to the behavior of the temperature of anisotropies and of the spin rotation inside the domain walls of a thin NiO layer. The blocking temperature of T[SUBB]=220 K is much higher than that observed in ferromagnetic/thin NiO systems with in-plane anisotropy. [ABSTRACT FROM AUTHOR]

It has been proposed earlier that the extraordinary magnetoresistance (EMR) observed at room temperature in nonmagnetic semiconducting materials containing metallic inhomogeneities can be used in suitably constructed read heads for magnetic storage devices. Here, we show that such read heads are much simpler in design, and allow for higher sensitivity than is observed using magnetic layered structures that employ the phenomenon of giant magnetoresistance. We calculate, with no adjustable material parameters, the room-temperature response of an EMR read-head design, using finite element analysis, as a function of the position of the magnetic bit relative to the read head. The scaling property of the EMR bodes well for increasing the storage density to 1 Tbit/in.[SUP2] in the near future. [ABSTRACT FROM AUTHOR]

The reproducible magnetic switching of submicron magnetic tunnel junctions (MTJ's) is an important requirement for their application in highly integrated magnetic memory devices. We have investigated the switching of small MTJ's by atomic and magnetic force microscopy (AFM/MFM) combined with micromagnetic numerical simulations. The latter are carried out with the real (AFM) shape as input mask, including the boundary roughness of the MTJ's. MFM reveals S-, C-, and Kshaped magnetization patterns for rectangular submicron sized junctions in saturation. In general, the magnetization loops and switching fields are different for individual junctions. The simulations show that the detailed boundary shape, which is specific for each junction, has a significant influence on the nucleation and location of domain walls and vortices, and hence, on the magnetic switching. [ABSTRACT FROM AUTHOR]

This article describes an approach for implementing a complete computer system (CPU, RAM, I/O, and nonvolatile mass memory) on a single integrated-circuit substrate (a chip)—hence, the name “single-chip computer.” The approach presented combines advances in the field of microelectromechanical systems (MEMS) and micromagnetics with traditional low-cost very-large-scale integrated circuit style parallel lithographic manufacturing. The primary barrier to the creation of a computer on a chip is the incorporation of a high-capacity [many gigabytes (GB)] re-writable nonvolatile memory (in today’s terminology, a disk drive) into an integrated circuit (IC) manufacturing process. This article presents the following design example: a MEMS-based magnetic memory that can store over 2 GB of data in 2 cm2 of die area and whose fabrication is compatible with a standard IC manufacturing process. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the low stiction/low glide height head-disk interface for high-performance disk drives. Experimental details; Results and discussion; Conclusions.

Abstract Magnetization switching by injected spin-polarized current or applied field pulses is considered for perpendicular magnetic nanosystems with uniaxial symmetry and subject to thermal fluctuations. Such systems can model both perpendicular spin-transfer-torque magnetic random access memories and magnetic grains for state-of-the-art perpendicular recording. It is shown that, in the limit of high energy barriers and large current/field amplitudes, the probability and cumulative distribution functions of switching times can be analytically computed as function of material, geometrical parameters and thermal noise level. The theoretical predictions are confirmed by macrospin and full micromagnetic simulations. By using the derived formulas, it is shown that analysis of Write-Error Rates (WERs) at typical levels of reliability required by magnetic recording technology can be easily performed. [ABSTRACT FROM AUTHOR]

Highlights • Split-CoFeB layers show higher tendency to promote PMA compared to non-split ones. • Saturation magnetization is higher at split-CoFeB layers compared to non-split ones. • Gilbert damping is moderately higher in split-CoFeB layers compared to non-split ones. • Split-CoFeB layers combine high magnetic anisotropy and moderate Gilbert damping. Abstract We report on the static and dynamic magnetic properties of W/CoFeB/Ta/CoFeB/MgO stacks, where the CoFeB layer is split in two by a 0.3 nm-thick Ta "dusting" layer. A total CoFeB thickness between 1.2 and 2.4 nm is studied. Perpendicular magnetic anisotropy is obtained for thickness below 1.8 nm even at the as-deposited stacks, and it is enhanced after annealing. Saturation magnetization is 1520 (1440) kA/m before (after) annealing, increased compared to non-split CoFeB layers. Ferromagnetic resonance measurements show that high magnetic anisotropy energy may be achieved (effective anisotropy field 0.571 ± 0.003 T), combined to a moderate Gilbert damping (0.030 ± 0.001). We argue that the above characteristics make the split-CoFeB system advantageous for spintronics applications. [ABSTRACT FROM AUTHOR]