Three-dimensional ferromagnetic architectures with multiple metastable states (original) (raw)
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2011 International Conference on Electromagnetics in Advanced Applications, 2011
We investigated the influence of 3-D magnetic layer geometry on switching in magneto-electronic devices. We found that the 3-D topography of magnetic layer must absolutely be taken into consideration during the design phase since their inherent nonplanarity profoundly affects their magnetization profile. Our initial results strongly indicate that the "non-flatness" of magnetic layer strongly influences the possible magnetic states, alters the switching mechanism and leads to totally new behavior, which was not observed in classic 2-D thin film magnetic structures. Our experimental results will be compared with detailed micromagnetic simulations.
Ferromagnetic vortices deliver robust out-of-plane magnetization at extremely small scales. Their handling and creation therefore has high potential to become a necessary ingredient for future data storage technologies in order to keep up with the pace of growing information density demands. In this study we show that by using one step nanolithography method, we are able to create ferromagnetic vortex lattices in thin nickel films. The necessary control of the magnetic stray field at the domain edges was achieved by actively modifying the ferromagnetic thin film anisotropic properties at nanometer scale. We present experimental evidence using ferromagnetic resonance and magnetoresistance measurements supporting simulations based on the theoretical prediction of the proclaimed vortex structures.
Towards a six-state magnetic memory element
Applied Physics Letters, 2016
We pattern permalloy films into three crossing elongated ellipses with an angle of 60 between the major axes of any pair of ellipses. Planar Hall effect measurements show that the magnetization in the area of overlap of the ellipses has six stable magnetic orientations parallel to the major axes of the three ellipses. We determine the effective anisotropy field for small magnetic deviations from the easy axis and the switching field between the easy axes as a function of magnetic field orientation. We compare our results with micromagnetic simulations and present an effective Hamiltonian that captures the magnetic response. We show how such magnetic structures in a magnetic tunnel junction would result in a magnetic memory element with six distinct resistance states that could be written using spin-orbit torques. Published by AIP Publishing.
Proposal of a Single Nano-Magnet Memory Device
IEEE Electron Device Letters
We propose a non-volatile memory device using ferromagnetic (FM) contacts fabricated on a channel exhibiting spin-momentum locking observed in diverse materials with spin-orbit coupling like heavy metals and topological insulators. The writing is enabled by the current induced spin-orbit torque, which has been used previously to switch the storage layer of a magnetic tunnel junction (MTJ). The reading is enabled by a relatively lower current-induced spin voltage measurement through the FM contact, which is high or low depending on the magnetization direction for a particular current direction. This new read mechanism significantly reduces the fabrication difficulties compared with MTJ-based designs. Simpler interconnects and control circuits can be used, since both read and write currents share the same path. Our proposal offers on-cell reference voltage generation with a normal metal contact on the channel at the same position as the FM, which is expected to improve the performance in a large array. The estimated read signal based on available materials is smaller compared with MTJ, but the noise is also expected to be smaller in our metallic device compared with those involving tunnel barriers.
Implementation of 4-state nanomagnetic devices with shape anisotropy
Nanomagnetic memory and logic are currently seen as promising candidates to replace current digital computing architectures due to its superior energy-efficiency, non-volatility and propensity for highly dense and low-power applications. In this work, we investigate the use of shape engineering (concave and diamond shape) to introduce biaxial anisotropy in single domain nanomagnets, giving rise to multiple easy and hard axes. Such nanomagnets, with dimensions of ~ 100 nm × 100 nm, double the logic density of conventional two-state nanomagnetic devices by encoding more information (four binary bits: "00","11","10","01") per nanomagnet and can be used in memory and logic devices as well as in higher order information processing applications. We study reliability, magnetization switching coherence, and show, for the first time, the use of voltage-induced strain for the clocking of magnetization in these four-state nanomagnets. Critical parameters such as size, thickness, concavity, and geometry of two types of four-state nanomagnets are also investigated. This analytical study provides important insights into achieving reliable and coherent single domain nanomagnets and low-energy magnetization clocking in four-state nanomagnets, paving the way for potential applications in advanced technologies.
2018
A next-generation memory device utilizing a three-dimensional nanowire system requires the reliable control of domain wall motion. In this letter, domain walls are studied in cylindrical nanowires consisting of alternating segments of cobalt and nickel. The material interfaces acting as domain wall pinning sites, are utilized in combination with current pulses, to control the position of the domain wall, which is monitored using magnetoresistance measurements. Magnetic force microscopy results further confirm the occurrence of current assisted domain wall depinning. Data bits are therefore shifted along the nanowire by sequentially pinning and depinning a domain wall between successive interfaces, a requirement necessary for race-track type memory devices. We demonstrate that the direction, amplitude and duration of the applied current pulses determine the propagation of the domain wall across pinning sites. These results demonstrate a multi-bit cylindrical nanowire device, utilizin...
2007
The large saturation magnetization in conventional dense moment ferromagnets offers flexible means of manipulating the ordered state through demagnetizing shape anisotropy fields but these dipolar fields, in turn, limit the integrability of magnetic elements in information storage devices. We show that in a (Ga,Mn)As dilute moment ferromagnet, with comparatively weaker magnetic dipole interactions, locally tunable magnetocrystalline anisotropy can take the role of the internal field which determines the magnetic configuration. Experiments and theoretical modeling are presented for lithographically patterned microchannels and the phenomenon is attributed to lattice relaxations across the channels. The utility of locally controlled magnetic anisotropies is demonstrated in current induced switching experiments. We report structure sensitive, current induced in-plane magnetization switchings well below the Curie temperature at critical current densities 10^5 Acm^-2. The observed phenome...
Magnetoresistive memory in ferromagnetic (Ga,Mn)As nanostructures
Magneto-resistive nanostructures have been investigated. The structures were fabricated by electron beam lithography patterning and chemical etching from thin epitaxial layers of the ferromagnetic semiconductor (Ga,Mn)As, in shape of three nanowires joined in one point and forming three-terminal devices, in which an electric current can be driven through any of the three pairs of nanowires. In these devices, a novel magneto-resistive memory effect has been demonstrated, related to a rearrangement of magnetic domain walls between different pairs of nanowires in the device consisting in that its zero-field resistance depends on the direction of previously applied magnetic field. The nanostructures can thus work as twostate devices providing basic elements of nonvolatile memory cells.
Three dimensional magnetic abacus memory
Scientific Reports, 2014
Stacking nonvolatile memory cells into a three-dimensional matrix represents a powerful solution for the future of magnetic memory. However, it is technologically challenging to access the data in the storage medium if large numbers of bits are stacked on top of each other. Here we introduce a new type of multilevel, nonvolatile magnetic memory concept, the magnetic abacus. Instead of storing information in individual magnetic layers, thereby having to read out each magnetic layer separately, the magnetic abacus adopts a new encoding scheme. It is inspired by the idea of second quantisation, dealing with the memory state of the entire stack simultaneously. Direct read operations are implemented by measuring the artificially engineered 'quantised' Hall voltage, each representing a count of the spin-up and spin-down layers in the stack. This new memory system further allows for both flexible scaling of the system and fast communication among cells. The magnetic abacus provides a promising approach for future nonvolatile 3D magnetic random access memory.