http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

https://dr.ntu.edu.sg/bitstream/10356/146755/2/Published_Spintronics%20based%20random%20access_a%20review.pdf

Spintronics based random access memory: a review

This paper formulates a general analytic approach to the theory of microwave generation in magnetic nano-structures driven by spin-polarized current and reviews analytic results obtained in this theory. The proposed approach is based on the universal model of an auto-oscillator with negative damping and nonlinear frequency shift. It is demonstrated that this universal model, when applied to the case of a spin-torque oscillator (STO) based on a current-driven magnetic nano-pillar or nano-contact, gives adequate description of most of the experimentally observed properties of STO. In particular, the model describes the power and frequency of the generated microwave signal as functions of the bias current and magnetic field, predicts the magnitude and properties of the generation linewidth, and explains the STO behavior under the influence of periodic and stochastic external signals: frequency modulation, phase-locking to external signals, mutual phase-locking in an array of STO, broadening of the generation linewidth near the generation threshold, etc. The proposed nonlinear auto-oscillator theory is rather general and can be used not only for the development of practical nano-sized STO, but, also, for the description of nonlinear auto-oscillating systems of any physical nature.

Nonlinear Auto-Oscillator Theory of Microwave Generation by Spin-Polarized Current

A magnetoresistive element according to an embodiment includes: a first ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a second ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a nonmagnetic layer placed between the first ferromagnetic layer and the second ferromagnetic layer; a first interfacial magnetic layer placed between the first ferromagnetic layer and the nonmagnetic layer; and a second interfacial magnetic layer placed between the second ferromagnetic layer and the nonmagnetic layer The first interfacial magnetic layer includes a first interfacial magnetic film, a second interfacial magnetic film placed between the first interfacial magnetic film and the nonmagnetic layer and having a different composition from that of the first interfacial magnetic film, and a first nonmagnetic film placed between the first interfacial magnetic film and the second interfacial magnetic film

Magnetoresistive element and magnetic memory

Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications. However, so far, the development of industrially attractive prototypes has been hampered by the inability to identify systems that can provide enough power. Here, we demonstrate that microwave signals with device-compatible output power levels can be generated from a single magnetic tunnel junction with a lateral size of 100 nm, seven orders of magnitude smaller than conventional radio-frequency oscillators. We find that in MgO magnetic tunnel junctions the perpendicular torque induced by the spin-polarized current on the local magnetization can reach 25% of the in-plane spin-torque term, although showing a different bias dependence. Both findings contrast with the results obtained on all-metallic structures, previously investigated, reflecting the fundamentally different transport mechanisms in the two types of structure. Improvements in the microwave output efficiency of MgO-based magnetic tunnel junctions brings them a step closer to practical applications and enables greater insight into the physics of spin transfer in such devices.

Bias-driven high-power microwave emission from MgO-based tunnel magnetoresistance devices

The present invention provides a tunneling magneto-resistive read sensor structure that improves sensitivity and linear density of the sensor structure. The sensor includes first and second electrodes and a stack positioned between the electrodes. The stack includes first and second free layers with magnetization orientations that are biased relative to each other. A tunneling barrier (insulating layer) or non-magnetic metal spacer is positioned between the first and second free layers. A sense current is passed between the first and second free layers of the stack. The amount of current passing through the first and second free layer changes based upon the orientation of the first and second free layers relative to each other.

Structure to achieve sensitivity and linear density in tunneling GMR heads using orthogonal magnetic alignments

A magnetic memory cell having a ferromagnetic free layer and a ferromagnetic pinned reference layer, each having an out-of-plane magnetic anisotropy and an out-of-plane magnetization orientation and switchable by spin torque. The cell includes a ferromagnetic assist layer proximate the free layer, the assist layer having a low magnetic anisotropy less than about 500 Oe. The assist layer may have in-plane or out-of-plane anisotropy.

Magnetic stack having assist layer

Multilevel cell is an important concept to improve the density of spin transfer torque memory. We demonstrated two-bit multilevel cell spin transfer switching using MgO-based magnetic tunnel junctions. Two types of cell structural design are discussed. Multiple resistance levels are depicted in a current-driven spin transfer switching loop, which shows a switching current density of ∼2×106A∕cm2. Reversible transitions between high and low states of the soft bit are achieved using minor-loop spin transfer switching. The influence of external magnetic field to spin transfer switching is also discussed.

Demonstration of multilevel cell spin transfer switching in MgO magnetic tunnel junctions

A resistive random access memory (RRAM) cell that includes a first electrode having a lower portion, a continuous side portion and an upper portion, the lower portion and the continuous side portion having an outer surface and an inner surface; a resistive layer having a lower portion, a continuous side portion and an upper portion, the lower portion and the continuous side portion having an outer surface and an inner surface; and a second electrode having a lower portion, an upper portion and an outer surface; wherein the outer surface of the resistive layer directly contacts the inner surface of the first electrode.

Structures for resistive random access memory cells

Measurements of noise properties of MgO-based magnetic tunnel junctions were performed in the frequency range from 100MHzto18GHz. A pronounced narrow peak at the frequency of around 7GHz with a full width at half-maximum as low as 21MHz has been observed. The peak amplitude and 1∕f noise have a threshold dependence on the dc bias current. The narrow peak is present only at one current polarity for an antiparallel orientation of the magnetic layers adjacent to the barrier, which is consistent with spin-momentum transfer theoretical predictions.

Zheng Gao

Papers

Structure to achieve sensitivity and linear density in tunneling GMR heads using orthogonal magnetic alignments

Magnetic stack having assist layer

Demonstration of multilevel cell spin transfer switching in MgO magnetic tunnel junctions

Structures for resistive random access memory cells

Spin transfer stimulated microwave emission in MgO magnetic tunnel junctions