A5040764734- Magnetic properties of thin films
- Advanced Memory and Neural Computing
- Magnetic Properties and Applications
- Theoretical and Computational Physics
- Transition Metal Oxide Nanomaterials
- Ferroelectric and Negative Capacitance Devices
- Quantum and electron transport phenomena
- Magneto-Optical Properties and Applications
- ZnO doping and properties
- Characterization and Applications of Magnetic Nanoparticles
- Physics of Superconductivity and Magnetism
- Magnetic Properties of Alloys
- Ga2O3 and related materials
- Neural Networks and Reservoir Computing
- Advanced Condensed Matter Physics
- Advancements in Semiconductor Devices and Circuit Design
- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Semiconductor materials and devices
- Neural dynamics and brain function
- Neuroscience and Neural Engineering
- Low-power high-performance VLSI design
- Metamaterials and Metasurfaces Applications
- Magnetic Field Sensors Techniques
- Block Copolymer Self-Assembly
Western Digital (United States)
2015-2024
RWTH Aachen University
2021
Swiss Light Source
2021
Paul Scherrer Institute
2021
Hitachi Global Storage Technologies (United States)
2013-2015
New York University
2009-2014
Faculty of 1000 (United States)
2010-2014
Western Digital (Japan)
2013
University of Konstanz
2006-2010
Samsung (South Korea)
2009-2010
Bit Patterned Media (BPM) for magnetic recording provide a route to densities $>1 Tb/in^2$ and circumvents many of the challenges associated with conventional granular media technology. Instead bit on an ensemble random grains, BPM uses array lithographically defined isolated islands, each which stores one bit. Fabrication is viewed as greatest challenge its commercialization. In this article we describe fabrication method combines e-beam lithography, directed self-assembly block copolymers,...
Orthogonal spin-transfer magnetic random access memory (OST-MRAM) uses a spin-polarizing layer magnetized perpendicularly to free achieve large torques and ultrafast energy efficient switching. We have fabricated studied OST-MRAM devices that incorporate tunnel junction, which consists of an in-plane synthetic antiferromagnetic reference layer. Reliable switching is observed at room temperature with 0.7 V amplitude pulses 500 ps duration. The bipolar, occurring for positive negative polarity...
The effect of thermal fluctuations on spin-transfer switching has been studied for a broad range time scales (sub-ns to seconds) in model system, uniaxial thin film nanomagnet. nanomagnet is incorporated into spin-valve nanopillar, which subject spin-polarized current pulses variable amplitude and duration. Two physical regimes are clearly distinguished: long pulse duration regime, reversal occurs by assisted activation over an energy barrier, short large the probability determined spin...
Spin-transfer switching with short current pulses has been studied in spin-valve nanopillars perpendicularly magnetized free and reference layers. Magnetization as 300 ps is demonstrated. The pulse amplitude needed to reverse the magnetization shown be inversely proportional duration, consistent a macrospin spin-transfer model. However, duration boundary depends on applied field much more strongly than predicted by zero temperature results also demonstrate that there an optimal length...
Bit patterned media (BPM) provide an alternative to conventional granular thin film recording media, circumventing the challenges of managing grain size and its associated noise thermal stability issues in media. A viable fabrication strategy involves creation a master pattern by rotary-stage e-beam lithography directed self-assembly block copolymers, followed replication via UV-cure nanoimprint transfer magnetic ion beam etching. These steps have been demonstrated for 150 Gdot/cm <sup...
The spin structure of head-to-head domain walls in Ni80Fe20 structures is studied using high-resolution photoemission electron microscopy. quantitative phase diagram extracted from these measurements and found to exhibit two boundaries between vortex transverse walls. results are compared with available theoretical predictions micromagnetic simulations differences the experiment explained, taking into account thermal excitations. Temperature-dependent show a thermally activated...
Magnetic domain walls are found to exhibit quasiparticle behavior when subjected geometrical variations. Because of the spin torque effect such a in potential well is excited by an ac current leading dip depinning field at resonance for densities as low 2 x 10(10) A/m2. Independently frequencies transverse and vortex determined from dc voltage that develops due rectifying resonant wall oscillation. The dependence on injected density reveals strongly nonharmonic
We present an experimental study of domain wall motion induced by current pulses as well conventional magnetic fields at temperatures between 2 and 300 K in a 110 nm wide 34 thick ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ ring. observe that, contrast with field-induced motion, which is thermally activated process, the critical density for current-induced increases increasing temperature, implies reduction spin torque efficiency. The effect Joule heating due to measured taken into account obtain...
Using microwave currents, we excite resonances of geometrically confined pinned domain walls, detecting the resonance by rectification current. By applying magnetic fields, frequency wall oscillator can be tuned over a wide range. Increasing power leads to redshift due nonlinearity system. From this shift, directly deduce quantitative shape potential, so that complete characterization pinning potential is obtained.
Single-shot time-resolved resistance measurements have been used to determine the magnetization reversal mechanisms of orthogonal spin transfer magnetic random access memory (OST-MRAM) devices at nanosecond time scales. There is a strong asymmetry between antiparallel (AP) parallel (P) and P AP transitions under same pulse conditions. are shown occur by precession free layer magnetization, while transition typically direct, occurring in less than 200 ps. We associate with torques...
The magnetic dipolar coupling of head-to-head domain walls is studied in 350nm wide NiFe and Co nanostructures by high resolution imaging. We map the stray field a wall directly with sub-10-nm using off-axis electron holography find that intensity decreases as 1∕r distance. By x-ray circular dichroism photoemission microscopy, we observe spin structures interacting change from vortex to transverse walls, when distance between reduced below (77±5)nm for 27nm thick (224±65)nm 30nm elements....
The spin-torque switching of metallic nanopillar spin valves showing strong perpendicular anisotropy are studied. magnetic states the layers depend on extrinsic parameters such as field and dc current applied to device. A state diagram presents a comprehensive graph role those spin-valve response. After explaining how diagrams can be built different possible representation, experimental studied for devices influence lateral size, temperature, orientation shown. An analytical model purely...
Resistive switching devices, important for emerging memory and neuromorphic applications, face significant challenges related to the control of delicate filamentary states in oxide material. As a device switches, its rapid conductivity change is involved positive feedback process that would lead runaway destruction cell without current, voltage, or energy limitation. Typically, cells are directly patterned on MOS transistors limit but this approach very restrictive as necessary integration...
We present a two-current-pulse temporal correlation experiment to study the intrinsic subnanosecond nonequilibrium magnetic dynamics of nanomagnet during and following pulse excitation. This method is applied model spin-transfer system, spin valve nanopillar with perpendicular anisotropy. Two-pulses separated by short delay (< 500 ps) are shown lead same switching probability as single duration that depends on delay. demonstrates remarkable symmetry between excitation relaxation provides...
The stability of 2pi domain walls in ferromagnetic nanorings is investigated via calculation the minimum energy path that separates a wall from vortex state nanoring. Trapped domains are stable when they exist between certain types transverse walls, i.e., which edge defects on same side magnetic strip have equal sign and thus repel. Here barriers these configurations magnetization states obtained using string method. Due to geometry ring, two must be distinguished differ by their overall...
In this work, thin film (down to 10 nm) (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Cr xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Mott-oxide based nano-devices (electrode width down 120 are fabricated for the first time. The devices show volatile threshold switching and NDR caused by thermal feedback. Fast (<; ns)...
We report the free layer switching field distributions of spin-valve nanopillars with perpendicular magnetization. While are consistent a thermal activation model, they show strong asymmetry between parallel to antiparallel and reverse transition, energy barriers more than 50% higher for transitions. The inhomogeneous dipolar from polarizer is demonstrated be at origin this symmetry breaking. Interestingly, restored devices lithographically defined notch pair removed midpoint pillar...
We present switching field distributions of spin-transfer-assisted magnetization reversal in perpendicularly magnetized Co/Ni multilayer spin-valve nanopillars at room temperature. Switching measurements the free layer with a 50 nm×300 nm ellipse cross section were conducted as function current. The validity model that assumes spin-current-dependent effective barrier for thermally activated is tested by measuring under applied direct currents. show deviate significantly from double...
In this paper, we present a new compact model of threshold switching devices which is suitable for efficient circuit-level simulations. First, macro model, based on transistor circuit, was implemented in LTSPICE. Then, descriptive extracted and MATLAB, the model. This extended to develop physical that describes processes occur during switching. The derived comprises delay structure with few electrical components adjacent second junction. incorporates an internal state variable, crucial...
Abstract The pressure‐driven Mott‐transition in Chromium doped V 2 O 3 films is investigated by direct electrical measurements on polycrystalline with thicknesses down to 10 nm, and doping concentrations of 2%, 5%, 15%. A change resistivity nearly two orders magnitude found for 2% doping. simulation model based a scaling law description the phase transition percolative behavior resistor lattice developed. This used show that despite significant deviations film structure from single crystals,...
We present a fast generative modeling approach for resistive memories that reproduces the complex statistical properties of real-world devices. By training on extensive measurement data an integrated 1T1R array (6000 cycles 512 devices), autoregressive stochastic process accurately accounts cross-correlations between device switching parameters, while nonlinear transformations ensure agreement with joint cycle-to-cycle (C2C) and device-to-device (D2D) write distributions. In addition to...
We present temperature dependent switching measurements of the Co/Ni multilayered free element 75 nm diameter spin-valve nanopillars. Angular hysteresis as well field taken at low are in agreement with a model thermal activation over perpendicular anisotropy barrier. However, statistics (mean and variance) from 20 K up to 400 disagreement N\'{e}el-Brown that assumes independent barrier height field. introduce modified thats fit experimental data which we take $T^{3/2}$ dependence due...
The angular dependence of the depinning field vortex and transverse domain walls is determined experimentally for NiFe rings with nanometer size constrictions. From dependence, we are able to deduce potential landscape caused by constriction seen wall. minimum at notch position so that these pinned symmetrically inside constriction. Vortex a adjacent this can be from variation fields. Good agreement results micromagnetic simulations obtained.