Generation of practical random numbers (RNs) by a spintronics-based, scalable truly RN generator called “spin dice” was demonstrated. The generator utilizes the stochastic nature of spin-torque switching in a magnetic tunnel junction (MTJ) to generate RNs. We fabricated eight perpendicularly magnetized MTJs on a single-board circuit and generated eight sequences of RNs simultaneously. The sequences of RNs of different MTJs were not correlated with each other, and performing an exclusive OR (XOR) operation among them improved the quality of the RNs. The RNs obtained by performing a nested XOR operation passed the statistical test of NIST SP-800 with the appropriate pass rate.

We prepared MgO-based magnetic tunnel junctions having a CoFeB/Ru/CoFeB synthetic free layer in which magnetizations of the CoFeB layers were ferromagnetically coupled (F-coupled Sy) or antiferromagnetically coupled (AF-coupled Sy). We studied spin-transfer switchings to evaluate their thermal stability (Δ0=KV/kBT) and intrinsic switching current density (JC0). Although the free layers of two types showed nearly equal JC0, the Δ0 of F-coupled Sy was observed to be twice that of AF-coupled Sy. This difference is attributable to the shape magnetic anisotropy of the free-layer cells. Results show that F-coupled Sy is superior to AF-coupled Sy for memory applications.

We have developed a new type of nanocontact structure called a “sombrero-shaped” nano-contact for a spin torque oscillator (STO) based on magnetic tunnel junctions. This structure reduces the shunt current, which passes through the capping layer, and hence improves the magnetoresistance (MR) ratio to 46% compared with an MR ratio of 3% in conventional nano-contact structures. It also displays highly stable oscillation (Q=350) with high emission power over 2 µW. This is significant in the development of new spintronic devices such as nanosized microwave generators and highly sensitive nanoscale magnetic field sensors.

We have investigated the microstructure and the magnetic properties of FePt and Fe/FePt polycrystalline thin films with high coercivity. The L10 FePt particulate film deposited on a heated amorphous SiO2 substrate showed a large coercivity (Hc) as high as 23 kOe. Contrary to an epitaxially grown single crystal FePt film, the Hc did not show a drastic decrease when the film morphology changed from particulate to continuous. The polycrystalline film with a thickness of 100 nm exhibited a coercivity of 13 kOe in spite of its simple processing route. This high coercivity is attributed to the magnetic domain pinning at the grain boundaries. By depositing Fe layers on the particulate FePt films, an increase of remanence and energy product was observed as a result of the exchange coupling of the Fe and FePt layers.