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We experimentally investigate spin–orbit torque (SOT) switching of a hybrid exchange spring system (ESS) in which a Co/Pt with perpendicular magnetic anisotropy (PMA) is coupled to a CoFeB thin film with an in-plane (IP) magnetic anisotropy (IMA). The magnetization tilt angle from the out-of-plane can be easily tuned by varying the thickness of the IMA layer due to the competition between PMA and IMA layers. We find that the tilt angle is highly tuned from 0° to 90° over a small range of CoFeB thicknesses, from 0 to 1 nm. The tilted films with high thermal stability are promising materials for a zero/low field operating SOT magnetic random access memory (MRAM) or for a bit patterned magnetic recording media. IP current-induced magnetization switching of Co/Pt-CoFeB ESS is also studied, under an IP magnetic field ($H_{\mathrm {IP}}$). The current amplitude for the 45° tilt magnetization switching is almost independent of the $H_{\mathrm {IP}}$ ranged from 50 to 1000 Oe. This phenomenon might be due to the presence of the Dzyaloshinskii–Moriya interaction (DMI) and DMI effective field is expected to be less than 50 Oe. [ABSTRACT FROM AUTHOR]

Multi-junctional magnetic tunneling junction spin dice based on orthogonal spin-transfer devices, a new type of true random number (RN) generator (TRNG) is demonstrated in this paper. Orthogonal spin-transfer devices use a planar polarizer to push the free layer with perpendicular anisotropy to metastable state (high-energy state) when power is on. The stochastic precessional switching behavior in ferromagnetic free layer is utilized as the entropy source of the TRNG. Once the power is turned off, anisotropy field and demagnetization field relax the magnetization of free layer from metastable state to one of the two stable states, producing a random bit whose value is solely determined by the stochastic switching behavior. The generation and detection of random bits were summarized under the macrospin picture. RN sequences with high randomness can be produced steadily in the proposed TRNG with a wide operation range of temperature and applied current density. Furthermore, the RN sequences pass the statistical test of NIST SP-800 with an appropriate pass rate without any need of post-procession of data. Ease of design, ultrafast switching as well as high randomness of the bit sequences make the proposed TRNG a competitive device in information security field. [ABSTRACT FROM AUTHOR]