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We investigate the static switching modes of nanomagnets patterned from antiferromagnetically exchange-coupled magnetic multilayers, and compare them to nanomagnets having only dipole coupling between the ferromagnetic layers. Vibrating sample magnetometry experiments, supported by micromagnetic simulations, reveal two distinct switching mechanisms between the exchange-coupled and only dipolecoupled nanomagnets. The exchange-coupled nanomagnets exhibit gradual switching of the layers, dictated by the strong antiferromagnetic exchange coupling present between the layers. However, the layers of the only dipole-coupled nanomagnets show abrupt nucleation/growth type switching. A comprehensive understanding of the switching modes of such layered and patterned systems can add new insight into the reversal mechanisms of similar systems employed for spintronic and magnetologic device applications. [ABSTRACT FROM AUTHOR]

Extensive thermal micromagnetic simulations, based on experimental data and parameters, were performed to investigate the magnetization reversal in Co/Pt nanomagnets with locally reduced perpendicular anisotropy on the nanosecond range. The simulations were supported by experimental data gained on manufactured Co/Pt nanomagnets, as used in nanomagnetic logic. It is known that magnetization reversal is governed by two mechanisms. At pulse lengths longer than 100 ns, thermal activation dominates the magnetization reversal processes and follows the common accepted Arrhenius law. For pulse lengths shorter than 100 ns, the dynamic reversal dominates. With the help of thermal micro-magnetic simulations we found out that the point where the both mechanisms meet is determined by the damping constant α of the multilayer film stack. The optimization of ferromagnetic multilayer film stacks enables higher clocking rates with lower power consumption and, therefore, further improve the performance of pNML. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate that the stray field of a propagating transverse domain wall can switch chains of coupled nanomagnets (nanomagnet wires) to a magnetically ordered, low energy ground state. We fabricated nanomagnet wires consisting of 6 and 20 nanomagnets that were placed adjacent to a domain-wall conductor. Magnetic force microscope images clearly show the nanomagnet wire switching from an initial metastable state to an ordered ground state. This can be exploited for controlled order of nanomagnet switching and for energy-efficient clocking of nanomagnet logic devices. Reference structures were fabricated and characterized to prove our assumptions. [ABSTRACT FROM AUTHOR]

We report a clock/logic/input structure for nanomagnet logic (NML) that implements a two-input slant-based OR gate with both clocking and input programming through current pulses. The clock line is a copper conductor embedded in a Si substrate with CoFe as a flux concentrator. Inputs are implemented with overlaid and dedicated bias lines. The programmability of such inputs allows us to test the same NML device for all possible input combinations. Results are determined by magnetic force microscopy. This scheme is easy to fabricate and can control thicker (20–30 nm) input nanomagnets. Close proximity of bias lines in such a structure allows us to investigate the effect of overlapping bias fields. We also report micromagnetic simulations that relate the slant in the output magnet to the dimensions of the input nanomagnets required to effect proper logic operation. [ABSTRACT FROM AUTHOR]

We present the experimental realization of a full adder circuit using Nanomagnet Logic (NML). The circuit relies heavily on the properties of asymmetric slant magnets that allow robust operation and reduced footprint. We demonstrate stand-alone NML majority gates and wires, and interconnect these components into an NML full adder that functions properly for all 8 input combinations. To our knowledge, this is the first working implementation of an NML full adder from in-plane magnetized nanomagnets, and one of the very few existing non-electrical, room temperature nanoscale computing units. [ABSTRACT FROM AUTHOR]

Nanomagnet logic (NML) has received increasing attention as an alternative information processing technology given the potential for low energy dissipation, a relatively advanced experimental state of the art, and intangibles such as inherent radiation hardness and nonvolatility. In order to facilitate the integration of NML-based circuits with transistor-based circuits, a magnetic–electrical interface (MEI) is needed. This paper focuses on the output portion of MEI design, i.e., converting signals from the magnetic domain to the electrical domain. The basic idea of an MEI output is to employ fringing fields from an NML device to set the magnetization state of the free layer of a magnetic tunnel junction. A detailed study of four different MEI output designs is presented which considers metrics such as the clock energy required to set the output state, the magnetoresistance ratio, etc. Simulation-based analysis reveals the pros and cons of each design. A design where multiple NML devices (i.e., free layers) share a large synthetic antiferromagnet is most promising based on our simulation-based, quantitative analysis. [ABSTRACT FROM PUBLISHER]

Enhanced permeability dielectric (EPD) samples were fabricated in an ultra-high-vacuum magnetron sputtering system, and their magnetic properties were studied by a variable-temperature vibrating sample magnetometer. EPDs were fabricated with layers of CoFe forming uniform particles separated by MgO dielectric as insulator. The optimal sample has peak relative low-field permeability (\mur) of 452, saturation magnetization (Ms) of 636 emu/cm^3 and magnetization at 100 Oe (M100\ Oe) of 398 emu/cm^3. Effect of low temperature is discussed, and measurements show that the EPD remains superparamagnetic at 173 K; \mur, Ms and M100\ Oe values at reduced temperatures are higher than those at room temperature. The sample is ferromagnetic at 100 K. [ABSTRACT FROM PUBLISHER]

In nanomagnet logic (NML), tens-of-mT fields are required to initiate the ordering of nanomagnets, and clock them into their computational ground state. This work investigates material-based approaches that are being used to reduce the nulling clock field. As test cases, arrays of both standalone and coupled magnets are covered with enhanced-permeability dielectric (EPD) films. Experimental results demonstrate that EPDs can reduce the fields required to saturate standalone magnets along the hard-axis by 60%, and coupled magnets by 75%. Experiments show that the remanent magnetization of a nanomagnet array is unchanged after being coated with EPDs, demonstrating that no undesired remanence is added to the NML system. The 75% reduction in switching field translates to a 94% reduction in energy dissipation due to reduced Joule-heating of field-generating wires. [ABSTRACT FROM AUTHOR]

The switching behavior and the magnetization states of non-interacting Supermalloy (Ni79Fe16Mo5) nanomagnet arrays were studied by magnetic measurements and micromagnetic simulations. The switching-field distribution of the easy-axis hysteresis loop of the nanomagnets was broadened due to lithographic shape variations and thermal fluctuations. When cooled to a low temperature (100 K), the switching-field distribution of the loop was reduced and its squareness ratio became higher. We found strong remanent magnetization along the hard axes of the nanomagnets, indicating the presence of metastable states and end-domain states. An oscillating field with amplitude of 30 Oe was sufficient to destabilize these metastable states; however, a high oscillating field (amplitude > 250 Oe) is required to reduce the remanence to zero. [ABSTRACT FROM AUTHOR]