Electrical manipulation of magnetization switching in Co2FeAl alloy based magnetic tunnel junctions with in-plane and perpendicular magnetization
Electrical manipulation of magnetization switching, such as spin-transfer torque (STT) switching, electric-field-assistant magnetization switching, and spin-orbit torque (SOT) switching, has been attracting great attentions due to its applications in low-power-consumption spintronic devices, such as magnetoresistive random access memories (MRAMs) and non-volatile magnetic-logic circuits. Recent investigations of electrical manipulation of magnetization switching in magnetic tunnel junctions (MTJs) have mainly been carried out in CoFeB/MgO/CoFeB structures. However, the switching current density of those MTJs is still too high for the scaling of gigabit MRAMs. Therefore, the establishment of new ferromagnetic materials for MTJs is greatly desired.
Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions
We demonstrated spin-transfer magnetization switching using magnetic tunnel junctions (MTJs) with a full-Heusler alloy Co2FeAl (CFA). We prepared CFA (1.5 nm)/MgO/CoFe (4 nm) (“CFA-free”) and CFA (30 nm)/MgO/CoFeB (2 nm) (“CFA-reference”) MTJs on a Cr(001) layer. The intrinsic critical current density (Jc0) of the CFA-free (CFA-reference) MTJ was 29 MA/cm2 (7.1 MA/cm2). The larger Jc0 of the CFA-free MTJ is attributed to the significant enhancement of the Gilbert damping factor (∼0.04) of the CFA due to the Cr layer. The Jc0 of the CFA-reference is as small as that reported for typical CoFeB/MgO/CoFeB MTJs.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%