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An antiferromagnetic metal (AFM) rich in spin-orbit coupling is a promising solid for the application of electrical current induced magnetic switching, because not only can it rely on its Spin Hall Effect (SHE) to generate spin current, it might also provide exchange coupling field to replace an external field required for coherent magnetic switching. In this work, we study the current induced magnetic switching by using the antiferromagnetic IrMn. The switching current density based on the spin Hall effect of IrMn is on the order of 1x106 A/cm2, which is comparable to the heavy metal systems with a large spin Hall angle. We observe an interesting switching behavior, in that a complete binary switching occurs under an applied field in the range of 2.0 to 8.0 mT, however, from zero field up to 2.0 mT, switching is continuous and incomplete. We attribute this observation to the distribution of exchange bias field and the mixture of internal and external field, which is attested by magneto-optical Kerr effect microscope. Our study sheds light on the SHE in AFM materials and their application in field-free switching such as in spin-logic and magnetic random-access memory devices. [ABSTRACT FROM AUTHOR]

Spin–orbit torques (SOTs) provide an efficient way to electrically manipulate the magnetic order in spintronic devices. Compared with conventional ferromagnetic materials, ferrimagnetic materials have the advantages of antiferromagnetically coupled sublattices and induced ultrafast spin dynamics. In this paper, we study the current-induced magnetization switching in the ferrimagnetic Ta/GdFeCo/MgO system. Robust SOT-induced magnetization switching can be achieved at the magnetic compensation temperature point of around 70 K, where the magnetization is nearly zero and the coercivity can reach almost 3 T. The temperature dependence of the SOT efficiency is quantified by the second harmonic method, and the enhanced SOT efficiency near the magnetic compensation temperature is attributed to the negative exchange coupling between the two sublattices of CoFe and Gd. This work demonstrates the SOT switching of the nearly compensated ferrimagnet, with great potential for future magnetic interaction-free and ultrafast ferrimagnetic applications. [ABSTRACT FROM AUTHOR]

We study the impact of Mg insertion layer at the CoFeB|MgO interface on the domain wall depinning field and motion as well as other magnetic properties in a perpendicular magnetized Ta/CoFeB/Mg(wedged)/MgO structure. With the increase of the Mg layer from 0.4 nm to 0.8 nm, the field-induced domain wall moving velocity increases while the depinning field decreases. The minimum depinning field of around 10 Oe for as-grown sample and 7 Oe for annealed sample is found with a 0.8 nm Mg insertion layer, which is 2 times lower than the ones reported before. Further increase of the Mg layer leads to a lower velocity and higher depinning field. Similar phenomena happens to the magnetic properties such as the saturation magnetization and perpendicular magnetic anisotropy. Both for as-grown and annealed samples, the tendency is similar. This may be explained by the oxidation and crystallinity manipulation of the CoFeB|MgO interface. These results show an ultra-low depinning field in the Ta/CoFeB/MgO system as well as a possible way for controlling the depinning field. [ABSTRACT FROM AUTHOR]

A true random number generator based on perpendicularly magnetized voltagecontrolled magnetic tunnel junction devices (MRNG) is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA). This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA) effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps) by implementing a 64 × 64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit) due to the high energy efficiency of the voltage-controlled MTJ switching. [ABSTRACT FROM AUTHOR]

We studied the thermal stability of perpendicular magnetic anisotropy (PMA) in Ta/Mo/CoFeB/MgO/Ta films with and without inserted Mo layers. In the absence of a Mo layer, the films show PMA at annealing temperatures below 300 °C. On the other hand, the insertion of a Mo layer preserves PMA at annealing temperatures of up to 500 °C; however, a higher annealing temperature leads to the collapse of PMA. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) were used to study the microstructure of the films to understand the deterioration of PMA. The XPS results show that the segregation of Ta is partly suppressed by inserting a Mo layer. Once inserted, Mo does not remain at the interface of Ta and CoFeB but migrates to the surface of the films. The HRTEM results show that the crystallization of the MgO (001) texture is improved owing to the higher annealing temperature of the Mo inserted sample. A smooth and clear CoFeB/MgO interface is evident. The inserted Mo layer not only helps to obtain sharper and smoother interfaces but also contributes to the crystallization after the higher annealing temperature of films. [ABSTRACT FROM AUTHOR]