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The nanoSQUID is a powerful tool to study the magnetic properties of the nanoparticles at a microscopic level because a small capture improves the magnetic coupling between the SQUID and the nano-object under investigation. The ultra low intrinsic magnetic flux spectral noise of such devices allows to detect few tens of elementary magnetic moment (Bohr magnetons) per unit of bandwidth. Since the nanoSQUIDs are often employed as magnetic flux to current transducer, the sensors show a hysteretic current to voltage characteristic and the measurement method consists in measuring the variations of the critical current of the device related to the flux change in the SQUID loop due to the nanoparticles magnetization state. In particular, a characterization of iron oxide (Fe3O4) nanoparticles have been carried out by using Dayem nanobridges based nanoSQUIDs having a hole geometry with a loop diameter ranging from 0.5 µm to 2 µm patterned by electron beam lithography. The nanoSQUIDs characterization was performed at T = 4.2 K in an electro-magnetically controlled environment. An implemented feedback circuit has allowed to perform direct measurements of hysteresis loops. The measurements are very encouraging in view of a wide use of nanoSQUIDs for the nanomagnetism investigations.
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Main references:
Nanoparticle magnetization measurements by a high sensitive nano-superconducting quantum interference device
R Russo, C Granata, E Esposito, D Peddis, C Cannas, A Vettoliere
Applied Physics Letters 101, 122601 (2012)
Magnetic properties of iron oxide nanoparticles investigated by nanoSQUIDs
C Granata, R Russo, E Esposito, A Vettoliere, M Russo, A Musinu, D Peddis, D Fiorani
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