Magnetic tunnel junctions (MTJs) with ferromagnetic electrodes possessing a perpendicular magnetic easy axis are of great interest as they have a potential for realizing next-generation high-density non-volatile memory and logic chips with high thermal stability and low critical current for current-induced magnetization switching. To attain perpendicular anisotropy, a number of material systems have been explored as electrodes, which include rare-earth/transition-metal alloys, L1(0)-ordered (Co, Fe)-Pt alloys and Co/(Pd, Pt) multilayers. However, none of them so far satisfy high thermal stability at reduced dimension, low-current current-induced magnetization switching and high tunnel magnetoresistance ratio all at the same time. Here, we use interfacial perpendicular anisotropy between the ferromagnetic electrodes and the tunnel barrier of the MTJ by employing the material combination of CoFeB-MgO, a system widely adopted to produce a giant tunnel magnetoresistance ratio in MTJs with in-plane anisotropy. This approach requires no material other than those used in conventional in-plane-anisotropy MTJs. The perpendicular MTJs consisting of Ta/CoFeB/MgO/CoFeB/Ta show a high tunnel magnetoresistance ratio, over 120%, high thermal stability at dimension as low as 40 nm diameter and a low switching current of 49 microA.

We have investigated the effect of applied electric field EG on thickness dependent magnetic anisotropy of sputtered Co40Fe40B20 sandwiched with MgO and Ta. The range of CoFeB thickness explored is 2 nm and below. As the thickness is reduced, the easy axis of magnetization becomes perpendicular from in-plane. We show that perpendicular magnetic anisotropy of in-plane samples and coercivity of perpendicular samples can be modified by applying EG at room temperature. Furthermore, superparamagnetic behavior is observed for CoFeB layers with further reduced thickness below ≈0.9 nm, where electric-field effect is also observed below their blocking temperature.

The magnetic Y-branch nanojunction: Domain-wall structure and magneto-resistance Appl. Phys. Lett. 101, 102403 (2012) Kinetics of magnetization processes in a quasi-one-dimensional Ising superantiferromagnet [{CH3}3NH]CoCl3· 2H2O Low Temp. Phys. 38, 843 (2012) Depth-dependent magnetization reversal and spin structure of Fe/NiO exchange-coupled epitaxial bilayers Appl. Phys. Lett. 101, 082412 (2012) Magnetic domain wall induced, localized nanowire reversal

Defects with associated electron and nuclear spins in solid-state materials have a long history relevant to quantum information science going back to the first spin echo experiments with silicon dopants in the 1950s. Since the turn of the century, the field has rapidly spread to a vast array of defects and host crystals applicable to quantum communication, sensing, and computing. From simple spin resonance to longdistance remote entanglement, the complexity of working with spin defects is fast advancing, and requires an in-depth understanding of their spin, optical, charge, and material properties in this modern context. This is especially critical for discovering new relevant systems dedicated to specific quantum applications. In this review, we therefore expand upon all the key components with an emphasis on the properties of defects and the host material, on engineering opportunities and other pathways for improvement. Finally, this review aims to be as defect and material agnostic as possible, with some emphasis on optical emitters, providing a broad guideline for the field of solid-state spin defects for quantum information.

We investigate properties of perpendicular anisotropy magnetic tunnel junctions (MTJs) with a recording structure of MgO/CoFeB/Ta/CoFeB/MgO down to junction diameter (D) of 11 nm from 56 nm. Thermal stability factor (Δ) of MTJ with the structure starts to decrease at D = 30 nm. D dependence of Δ agrees well with that expected from magnetic properties of blanket film taking into account the change in demagnetizing factors of MTJs. Intrinsic critical current (IC0) reduces with decrease of D in the entire investigated D range. A ratio of Δ to IC0 shows continuous increase with decrease of D down to 11 nm.

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We investigate electric-field effects on the effective magnetic anisotropy energy density Keff and the Gilbert damping constant α in Ta/CoFeB/MgO structures with CoFeB thickness t ranging from 1.4 to 1.8 nm by ferromagnetic resonance. The electric field-induced modulation ratio of the areal energy density Kefft does not depend on the CoFeB thickness, indicating that the electric-field effect on the magnetic anisotropy originates from the modulation of CoFeB/MgO-interfacial magnetic anisotropy. A clear electric-field modulation of α is observed for the structure with t = 1.4 nm, and almost no modulation for the structures with t ≥ 1.5 nm.

We show the electric-field induced magnetization switching for CoFeB/MgO magnetic tunnel junctions with thick MgO barrier layer of 2.8 nm, whose resistance-area product is 176 kΩ μm2, and achieve the small switching energy of 6.3 fJ/bit. The increase of the junction resistance is expected to suppress the energy consumption due to the Joule heating during the switching; however, the energy is still dominated by the Joule energy rather than the charging energy. This is because the junction resistance decreases more rapidly for junctions with thicker MgO as bias voltage increases.