Since the discovery of the large spin Hall effect in certain heavy metals, there has been continuous interest in utilizing this spin-orbit torque (SOT) effect in constructing a non-volatile memory that can be switched by an electric current. The key to future application of this type of memory is achieving both a short write time and a low write current, which will lower the energy cost compared to existing and other emerging memory technologies. We demonstrate an efficient way of reducing the switching current in tungsten-based three terminal magnetic tunnel junctions (MTJs) with in-plane magnetization (IPM) using a sub-atomic layer of Hf dusting inserted between the free FeCoB layer and the MgO tunnel barrier. We show with a simple FeCoB-MgO-FeCoB MTJ structure that in addition to low write current, fast pulse switching can be achieved with pulses ≤ 1 ns. We also confirm that in an SAF balanced MTJ structure with a PtHf spin Hall channel that the nanosecond switching behavior is typical of the switching of IPM three terminal spin-orbit-torque devices. We report write error rate of these structures down to ~10<sup>-6 </sup>at for 1 ns pulses, demonstrating feasibility for high performance cache memory.
We have fabricated metal constrictions having diameters as small as 3 nm. This is narrow enough that effects due to
single defects within the constriction region are visible as changes in the resistance. We will discuss the voltage and
temperature dependence of the individual defect motion that can lead to electromigration in these samples. We will also
present observations of magnetic defects and the presence of time-independent conductance fluctuations in these ballistic