Physical properties of CeGe2-x (x=0.24) single crystals.

We present data on the anisotropic magnetic properties, heat capacity and transport properties of CeGe2-x (x=0.24) single crystals. The electronic coefficient of the heat capacity, γ∼110 mJ mol(-1) K(-2), is enhanced; three magnetic transitions, with critical temperatures of ≈7, ≈5 and ≈4 K are observed in thermodynamic and transport measurements. The ground state has a small ferromagnetic component along the c-axis. Small applied field, below 10 kOe, is enough to bring the material to an apparent saturated paramagnetic state (with no further metamagnetic transitions up to 55 kOe) with a reduced, below 1.2 µB, saturated moment.

Finite tunneling spin polarization at the compensation point of rare-earth-metal-transition-metal alloys.

We show, using superconducting tunneling spectroscopy and tunneling magnetoresistance measurements, that ferrimagnetic alloys of Co and Gd can exhibit both positive and negative spin polarization depending on temperature and composition. These observations can be understood by considering the relative contributions of independent spin-polarized tunneling currents from the rare-earth-metal and transition-metal subnetwork magnetizations, which are coupled antiferromagnetically. At the compensation point of the alloy, where the subnetwork magnetizations are equal and the alloy has nearly zero net magnetization, nevertheless large tunneling spin polarization is observed.

Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers.

Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.