Magnetic Susceptibility Study of Sub-Pico-emu Sample Using a Micromagnetometer: An Investigation through Bistable Spin-Crossover Materials

Abstract

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 × 10⁻⁴ mm³, of SCO particles is measured. The local probe of the experimental setup allows a highest resolution of 4 × 10⁻¹⁴ emu to be reached, which is never achieved by experimental methods at room temperature.

An original and ultrasensitive method based on the self-generated magnetic field of the magneto-resistive (MR) multi-ring sensor is developed to study the spin-switching in bistable spin-crossover materials. The spin transition of the lowest volume of SCO nanoparticles of 1 × 10^–4 mm³ is detected. The device allows a resolution of 4 × 10^–14 emu to be achieved at room temperature.

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