NanoSQUID magnetometry of individual cobalt nanoparticles grown by focused electron beam induced deposition

Abstract

We demonstrate the operation of low-noise nano superconducting quantum interference devices (SQUIDs) based on the high critical field and high critical temperature superconductor YBa${}_2$Cu${}_3$O${}_7$ (YBCO) as ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have been patterned by focused ion beam milling. This allows to precisely define the lateral dimensions of the SQUIDs so as to achieve large magnetic coupling between the nanoloop and individual MNPs. By means of focused electron beam induced deposition, cobalt MNPs with typical size of several tens of nm have been grown directly on the surface of the sensors with nanometric spatial resolution. Remarkably, the nanoSQUIDs are operative over extremely broad ranges of applied magnetic field (-1 T $<{\mu }_{0}H<$ 1 T) and temperature (0.3 K $<T<$ 80 K). All these features together have allowed us to perform magnetization measurements under different ambient conditions and to detect the magnetization reversal of individual Co MNPs with magnetic moments (1 - 30) $\times 10^6{\mu }_{\mathrm{B}}$. Depending on the dimensions and shape of the particles we have distinguished between two different magnetic states yielding different reversal mechanisms. The magnetization reversal is thermally activated over an energy barrier, which has been quantified for the (quasi) single-domain particles. Our measurements serve to show not only the high sensitivity achievable with YBCO nanoSQUIDs, but also demonstrate that these sensors are exceptional magnetometers for the investigation of the properties of individual nanomagnets.

References in corpus (1)

• Optimizing the spin sensitivity of grain boundary junction nanoSQUIDs -- towards detection of small spin systems with single-spin resolution

Cited by in corpus (7)

• Josephson junctions and SQUIDs created by focused helium ion beam irradiation of YBa${}_2$Cu${}_3$O${}_7$
• SQUID-on-tip with single-electron spin sensitivity for high-field and ultra-low temperature nanomagnetic imaging
• Vortex matching at 6 T in YBa${}_2$Cu${}_3$O${}_{7-\delta }$ thin films by imprinting a 20 nm-periodic pinning array with a focused helium ion beam
• Quantum Size Effects in the Magnetic Susceptibility of a Metallic Nanoparticle
• Magnetization Reversal Across Multiple Serial Barriers in a Single Fe${}_3$O${}_4$ Nanoparticle
• Superconducting microwave magnetometer for absolute flux detection
• Noise of a superconducting magnetic flux sensor based on a proximity Josephson junction