International audienceRecently, nanoscale spin-crossover (SCO) particles have been the subject of great interest. The change in the 3d electronic configuration of the metal ion results in significant changes in the metal-ligand bond length and geometry, as well as in the molecular volume. Hence the spin switching process is accompanied by a remarkable change in the color, mechanical properties, dielectric properties, and magnetic susceptibility. The synthesis and investigation of these materials at reduced length scales is central not only to the exploration of fundamental effects of size reduction in these systems, but also for the development of new functional materials with applications, including guest molecule sensing, memory devices, and molecular switche
Antisymmetric magneto-resistance anomalies generated by a reversal of the magnetization are studied in a number of GaMnAs/InGaAs layers with out-of-plane (easy axis) magnetization. The anomalies occur independent of the magnetic field orientation. This shows, that once a magnetic domain with reversed magnetization is nucleated, simply the presence of the domain wall between the longitudinal contacts is sufficient to give rise to the anomaly. Very different shapes for magneto-resistance anomaly can be observed experimentally depending upon the sample. They reflect the various magnetic domain structures present inside the layers during the magnetization reversal process.
A promising and original method to study the spin-transition in bistable spin-crossover (SCO) materials using a magnetoresistive multiring sensor and its self-generated magnetic field is reported. Qualitative and quantitative studies are carried out combining theoretical and experimental approaches. The results show that only a small part of matter dropped on the sensor surface is probed by the device. At a low bias-current range, the number of detected nanoparticles depends on the amplitude of the current. However, in agreement with the theoretical model, the stray voltage from the particles is proportional to the current squared. By changing both the bias current and the concentration of particle droplet, the thermal hysteresis of an ultrasmall volume, 1 × 10 mm , of SCO particles is measured. The local probe of the experimental setup allows a highest resolution of 4 × 10 emu to be reached, which is never achieved by experimental methods at room temperature.
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