Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200 ps, which is ten times faster than the natural damping time constant.
Rapid and specific rare cell detection for point-of-care testing requires an integration of the sample preparation for flow cytometry. To achieve such a challenging goal we have developed a magnetic flow cytometry technique which applies magnetophoresis to perform cell enrichment, focusing, and background elimination in a single step. Time-of-flight measurements are performed with integrated magnetic sensors to detect specifically cancer cells and cell diameters in whole blood.
We have fabricated field programmable spin-logic gates based on spin-dependent tunneling (SDT) elements. Here we show their feasibility down to a width of 0.6 μm of the SDT elements that form spin-logic gates. We further demonstrate the clocked operation of a hybrid spin-logic gate consisting of SDT elements and a semiconductor-based sense amplifier. Apart from the nonvolatility of the inputs, the output and the programming information, the experimentally demonstrated concept seems to be suitable for reconfigurable computing operations.
We report on the magnetic and transport properties of [IrMn8/CoFe1.5]/AlOx1.2/[CoFe1/NiFe5/CoFe1]/AlOx1.2/[CoFe1.5/IrMn8] (nanometer) double magnetic tunnel junctions (DMTJs) deposited by magnetron sputtering and patterned using optical lithography. The tunnel magnetoresistance (TMR) versus the bias voltage presents a symmetric characteristic, which indicates a good and similar quality of both AlOx barriers. The junctions show a resistance-area product about 35 kΩ μm2, a high TMR at room temperature of 49.5%, and a high bias voltage at which the TMR signal is decreased to half of its maximum value, V1/2DMTJ=1.33 V. Both hard magnetic layers are rigid in negative field up to 51.5 kA/m, while the coercive field of the soft layer is around 1.1 kA/m. The large difference of coercive fields, combined with the large TMR and V1/2, makes these systems very promising for spin electronic devices.
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