Spin-dependent conductance minima in magnetic tunnel junctions

Abstract

We present a study on the positions of conductance minima for the parallel and antiparallel magnetization configurations in magnetic tunnel junctions, both experimentally and theoretically. It is found that the conductance minima can have as much as a 100-mV shift from zero bias, and the shifts are spin dependent. These behaviors have not been observed in tunnel junctions based on nonmagnetic electrodes. By considering the voltage dependent density of states of ferromagnetic electrodes in the Brinkman model, the difference can be well explained. The results demonstrate that the density of states of the ferromagnetic electrodes play an important role in defining the bias dependence behaviors in magnetic tunnel junctions.

Spin-polarized transport in hybrid (Zn,Cr)Te∕Al2O3∕Co magnetic tunnel junctions

“…The barrier is fabricated by depositing a wedge-shaped Al layer, followed by in-situ plasma oxidation at 60 mTorr of oxygen for 120 s. MTJ samples with areas from 0.0078 to 0.125 mm 2 were defined by standard photolithography and ion-beam etching. 3,16 Transport measurements were performed using a four-probe technique. In our case, positive bias refers to current flowing from the top electrode to the bottom electrode.…”

“…After plasma oxidation, there are under-, optimal-and overoxidized regions along the Al wedge, similar to our previous studies. 16 Here we focus on the optimally oxidized MTJs that have the maximum TMR value. Figure 1͑a͒ shows the TMR curves at different temperatures for such junctions.…”

Probing tunnel barrier shape and its effects on inversed tunneling magnetoresistance at high bias

“…1,2 The common Al 2 O 3 barrier is typically formed by oxidizing around the 1.5-nm Al layer, and the barrier quality depends on the film roughness, grain size, and oxidation conditions. The barrier height and barrier thickness are often extracted from current-voltage curves using either Simmons' or Brinkman et al's model.…”

Direct measurement of barrier asymmetry inAlOx∕ZrOymagnetic tunnel junctions using off-axis electron holography

“…It is advantageous for applications because we can engineer the MTJs to work at maximum TMR under a specific bias. The asymmetric bias dependence has been studied in MTJs with dissimilar electrodes, such as Co/ Al 2 O 3 /Py ͑Py= Ni 81 Fe 19 ͒ junctions 11 and Co/ Al 2 O 3 / Co junctions with different crystal structures of Co. 12 It has also been studied in MTJs with the different barrier heights at the top and bottom interfaces as seen in a Co/ Cu/ Co/ Al 2 O 3 / Co junction where the steplike potential barrier was created by diffusing Cu into the Al 2 O 3 interface 13 and in FeCo/ TaO x / FeCo junctions where the asymmetric barrier was formed by different oxidation conditions. 14 Many techniques have been used to characterize the ultrathin barrier in MTJ.…”