130,643 research outputs found
Understanding dynamics of interacting magnetic nanoparticles: From the weak interaction regime to the collective superspin glass state
No full textExchange Bias in Fe@Cr Core-Shell Nanoparticles
No full textWe have used X-ray magnetic circular dichroism and magnetometry to study isolated Fe@Cr core-shell nanoparticles with an Fe core diameter of 2.7 nm (850 atoms) and a Cr shell thickness varying between 1 and 2 monolayers. The addition of Cr shells significantly reduces the spin moment but does not change the orbital moment. At least two Cr atomic layers are required to stabilize a ferromagnetic/antiferromagnetic interface and generate the associated exchange bias and increase in coercivity. RI Kroeger, Roland/D-5321-2012; Lari, Leonardo/D-6844-2012; Peddis, Davide/J-8556-201
Hysteretic NanoSQUID Sensors for Investigation of Iron Oxide Nanoparticles
No full textMagnetic nanosensors based on niobium nano superconducting quantum interference device (nanoSQUID) have been fabricated and employed to investigate the magnetic properties of iron oxide nanoparticles. The nanoSQUIDs, fabricated by electron beam lithography, consist in a square loop interrupted by two nanometric constrictions (Dayem bridges). The flux capture area is 0.5 mu m(2) while the Dayem nanobridges have a width and a length ranging from 50 to 90 nm and 70 to 80 nm, respectively. Measurements of current to voltage (I-V) and critical current to magnetic flux (I-C-Phi) characteristics have been reported for different nanobridge dimensions. At T = 4.2 K the nanosensors have shown a hysteretic I-V characteristic and a triangular shaped I-Phi pattern suggesting a strong deviation from sinusoidal current-phase relationship. Due to the hysteretic behavior, the devices have been employed as a magnetic flux to current transducer. In such a configuration an overall magnetic flux resolution of about 0.3 m Phi(0) has been estimated. These nanosensors have been successfully employed to measure the field dependence and the time relaxation of the magnetization of iron oxide nanoparticles having a mean diameter of 4.2 nm. The experimental curves undoubtedly prove that the nanoSQUIDs reported here can be successfully employed to investigate the magnetic properties of very small nanoparticles. RI Peddis, Davide/J-8556-2013; Russo, Roberto/A-8576-2010 OI Russo, Roberto/0000-0001-9431-626
Memory Effects in Ultra-Small CoFe2O4 Nanoparticles
No full textWe have employed the Monte Carlo (MC) simulation technique to study the aging effect on the Zero-Field-Cooled (ZFC) magnetization curves of ultra-small CoFe2O4 nanoparticles (mean size similar to 3 nm) embedded in a Si matrix. We consider spherical nanoparticles consisting of an ordered ferrimagnetic core and a ferrimagnetic disordered surface. The spins in the particles interact with nearest neighbors Heisenberg exchange interaction. Our simulations show that the spin-glass like disorder at the surface affects the magnetic properties to the extent that they exhibit aging effect: the low temperature ZFC magnetization depends on the time (waiting time, t(W)) spent before applying the magnetic field at a temperature at which most of the surface moments are frozen. The results of our MC simulations are in good agreement with the experimental findings confirming that the random freezing of surface spins is responsible for the aging effect
Time and temperature dependent magnetic viscosity experiments on Sr/Co nanoferrite particles
No full textMagnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19-CoFe2O4 nanocomposites). The magnetic viscosity S = d M ( t ) / d l n ( t ) , where M ( t ) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field H s a t considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes
Magnetic properties of iron oxide nanoparticles investigated by nanoSQUIDs
No full textMagnetization measurements of Fe3O4 nanoparticles have been performed by using a nanosized superconducting quantum interference device (nanoSQUID). The nanosensor consists of a niobium loop having an area of 0.5 mu m(2) interrupted by two Dayem nanobridges. The device fabrication procedure is based on the electron beam lithography, thin film deposition and the lift-off technique. The characterization of the nanodevice at T = 4.2 K includes measurements of current-voltage, critical current vs. magnetic flux characteristic and flux noise. A proper feedback circuit has been employed to increase the dynamic range of the nanosensor. The magnetic nanoparticles under investigation have a diameter of 4 nm and 8 nm and were synthesized by thermal decomposition of metallorganic precursors in the presence of oleic acid and oleylamine as surfactants and organic solvent with high boiling point. Measurements of magnetization as a function of the external magnetic field for both nanoparticle diameters are reported at liquid helium temperature. In both cases, it can be observed an evident magnetic hysteresis indicating a blocking temperature well above 4.2 K. The reliability and the clarity of the reported measurement demonstrates that a low noise nanoSQUID is a powerful tool to investigate the properties of magnetic nano-objects. RI Peddis, Davide/J-8556-2013; Russo, Roberto/A-8576-2010 OI Russo, Roberto/0000-0001-9431-626
Structural, microstructural and magnetic properties of (La1-xCax)MnO3 nanoparticles
No full textThe crystal and magnetic structures of 10 and 20 nm sized (La1-xCax)MnO3 (x = 0.37, 0.50, 0.75) have been investigated between 5 and 300 K by means of Rietveld refinement of neutron powder diffraction data, coupled with transmission electron microscope observation and magnetization measurements. TEM observation reveals that nanoparticles are strongly affected by strain fields, probably originating from surface pressure. Irrespective of the composition, charge and orbital orderings are suppressed and F-z and C-y spin orderings coexist at low temperature; C-y and F-z orderings likely occur within the strained regions of the nanoparticles and in the matrix respectively. Moreover G(z) and A(z) orderings are sometimes observed, and are likely to be taking place at the border of the strained regions. RI Peddis, Davide/J-8556-201
Ferroic Transition Metal Oxide Nano‐heterostructures: From Fundamentals to Applications
No full textNanostructured transition metal oxides (TMOs) showing a ferroic order have attracted a great deal of attention over the last two decades both for fundamental studies and for technological applications in different fields, such as information storage/processing, sensors, biomedicine, and energy. The strong coupling between charge, spin, orbital, and lattice symmetry in complex TMOs gives rise to a wide range of physical properties, including magnetism, ferroelectricity, piezoelectricity, multiferroicity, and colossal magnetoresistance, which can be finely tuned by varying the chemical composition and crystal structure. Spurred by recent advances in synthesis and characterization techniques, the interfacial effect in heterostructures combining two or more different oxides has emerged as a powerful tool to further engineer the final properties in ferroic oxides. Following a brief overview on the ferroic properties of nanostructured complex TMOs, topical examples of different nanostructured oxide heterostructures and their potential applications will be illustrated
Focus on Metastable, Amorphous and Nanostructured Materials: Editorial note for the special issue - ISMANAM 2018
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