Spin torque switching is investigated in perpendicular magnetic tunnel junctions using Ta∣CoFeB∣MgO free layers and a synthetic antiferromagnet reference layer. We show that the Ta∣CoFeB interface makes a key contribution to the perpendicular anisotropy. The quasistatic phase diagram for switching under applied field and voltage is reported. Low switching voltages, Vc 50 ns=290 mV are obtained, in the range required for spin torque magnetic random access memory. Switching down to 1 ns is reported, with a rise in switching speed from increased overdrive that is eight times greater than for comparable in-plane devices, consistent with expectations from a single-domain model.

The role of grain boundaries in the magnetoresistance ͑MR͒ properties of the manganites has been investigated by comparing the properties of epitaxial and polycrystalline films of La 0.67 D 0.33 MnO 3Ϫ␦ (DϭCa, Sr, or vacancies͒. While the MR in the epitaxial films is strongly peaked near the ferromagnetic transition temperature and is very small at low temperatures, the polycrystalline films show large MR over a wide temperature range down to 5 K. The results are explained in terms of switching of magnetic domains in the grains and disorder-induced canting of Mn spins in the grain-boundary region. ͓S0163-1829͑96͒51746-7͔

Dynamic state switching in nonlinear multiferroic cantilevers Appl. Phys. Lett. 101, 043506 (2012) Nanomagnetism of cobalt ferrite-based spin filters probed by spin-polarized tunneling Appl. Phys. Lett. 101, 042409 (2012) Magnetic Schottky diode exploiting spin polarized transport in Co/p-Si heterostructure Appl. Phys. Lett. 100, 262402 (2012) Concepts and steps for the realization of a new domain wall based giant magnetoresistance nanowire device: From the available 24 multiturn counter to a 212 turn counter Exchange biased magnetic tunnel junction ͑MTJ͒ structures are shown to have useful properties for forming magnetic memory storage elements in a novel cross-point architecture. MTJ elements have been developed which exhibit very large magnetoresistive ͑MR͒ values exceeding 40% at room temperature, with specific resistance values ranging down to as little as ϳ60 ⍀͑m͒ 2 , and with MR values enhanced by moderate thermal treatments. Large MR values are observed in magnetic elements with areas as small as 0.17 ͑m͒ 2 . The magnetic field dependent current-voltage characteristics of an MTJ element integrated with a silicon diode are analyzed to extract the MR properties of the MTJ element itself.

We demonstrate a method for measuring magnetoresistance (MR) and resistance area product (RA) of unpatterned magnetic tunnel junction film stacks. The RA is measured by making a series of four point probe resistance measurements on the surface of an unpatterned wafer at various probe spacings. The key to this technique is in placing the probes at the appropriate spacings, on the order of microns for typical applications. The MR is obtained by repeating the measurement at different magnetic fields. A simple conceptual model and an exact analytical solution in good agreement with experimental data are presented. The current-in-plane tunneling method requires no processing, is fast, and provides reliable data which are reflective of the deposition only.

Spin-transfer torque magnetic random access memory (STT-MRAM) is one of the most promising emerging non-volatile memory technologies. MRAM has so far been demonstrated with a unique combination of density, speed, and non-volatility in a single chip, however, without the capability to replace any single mainstream memory. In this paper, we demonstrate the basic physics of spin torque switching in 20 nm diameter magnetic tunnel junctions with perpendicular magnetic anisotropy materials. This deep scaling capability clearly indicates the STT MRAM device itself may be suitable for integration at much higher densities than previously proven.