MgO-based magnetic tunnel junctions with up to 230% tunnel magnetoresistance ratio at room temperature and up to 345% at 13 K are prepared. The lower electrode is either exchange-biased or free, while the top electrode is free or an exchanged-biased artificial ferrimagnet, respectively. Additionally, a pseudo-spin-valve ͑hard-soft switching͒ design with two unpinned electrodes is used. Inelastic electron-tunneling spectra for each of these systems show a strong variation in the zero-bias anomaly with a reduced peak for some of the junctions. At voltages around 200 mV additional structures are found, which are not known from junctions with lower magneto resistance, such as alumina-based junctions. We discuss the spectra for the different electrode types and compare our findings with respect to barrier material and magnetoresistance ratio.

The transport properties of Co 2 MnSi/ AlO x / Co-Fe magnetic tunnel junctions showing a tunnel magnetorestistance of 95% at low temperatures are discussed with respect to temperature-dependent magnetic moments at the Co 2 MnSi/ AlO x interface and electronic band structure effects. These junctions show a considerably larger temperature and bias voltage dependence of the tunneling magnetoresistance compared to Co-Fe -B/AlO x / Co-Fe-B junctions, although the effective spin polarization of Co 2 MnSi ͑66%͒ is larger than CoFe-B ͑60%͒. Especially, the tunnel magnetoresistance of the Co 2 MnSi based junctions becomes inverse for large bias voltages. With increasing atomic disorder of the interfacial Co 2 MnSi its magnetic moments decrease and show a stronger temperature dependence. Even for the best atomic ordering achieved the corresponding spin-wave parameters of Mn and Co at the Co 2 MnSi/ AlO x interface are significantly larger than expected for Co 2 MnSi bulk and also larger than the spin-wave parameters of Co and Fe at a Co-Fe-B / AlO x interface. The influence of enhanced interfacial magnon excitation in the Co 2 MnSi/ AlO x / Co-Fe junctions on their transport properties will be discussed as well as possible origins for the negative tunnel magnetoresistance at high bias voltages.

The time-dependent dielectric breakdown has been investigated in Co–Fe–B/MgO/Co–Fe–B junctions by voltage ramp experiments and focused on its dependence on the barrier thickness, junction area, polarity of the applied voltage, ramp speed, and annealing temperature. The results suggest that the breakdown voltage strongly depends both on the polarity of the applied voltage and the annealing temperature. Magnetic tunnel junctions (MTJs) with positive bias on the top electrode show higher breakdown voltage than MTJs with negative bias. We found that there is a significant decrease in the breakdown voltage when the annealing temperature is increased above 350 °C.

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It is a truth universally acknowledged that a Heusler compound in possession of a good order must be in want of a high spin polarization. In the present work, we investigated the spin polarization of the Heusler compound Co2FeAl by spin polarized tunneling through a MgO barrier into a superconducting Al–Si electrode. The measured spin polarization of P=55% is in good agreement with the previously obtained tunnel magnetoresistance values and compared to the data by other groups.