Paramagnetic Meissner Effect in Nb Disks

Further details of the zero-field-cooled-magnetization and field-cooled-magnetization results on Nb disks exhibiting the paramagnetic Meissner effect (PME) are described. These studies indicate that two well-defined temperatures can be associated with features in the magnetization results. The higher characteristic temperature Tu is correlated with appearance of the paramagnetic moment and is strongly dependent upon the process used in forming the disk-shaped geometry of these Nb samples. The lower temperature Tp is associated with the “intrinsic coupling” of the interior Nb platelets. These latest results are shown to be consistent with the flux compression model for the appearance of the PME

Modeling of Hysteresis and Magnetization Curves for Hexagonally Ordered Electrodeposited Nanowires

A computational model has been developed to investigate how the magnetostatic interactions affect the hysteresis and magnetization curves for hexagonal arrays of magnetic nanowires. The magnetization coupling between nanowires arises from the stray fields produced by the other nanowires composing the array such that the field at each nanowire is the sum of the external field and the interaction field with the other nanowires. Using only two adjustable parameters: the interaction between nearest neighbors and the width of the Gaussian distribution in switching fields centered around the measuredcoercivity, simulations are compared with the experimentally measuredhysteresis and magnetization curves for electrodepositedCo0.45 Fe0.55 alloy nanowires with diameters from 12 to 48 nm. Excellent agreement is found for all nanowire systems except for the largest diameter arrays where deviations from the Gaussian distribution of switching fields need to be considered

Fabrication and Characterization of Co1−xFex Alloy Nanowires

Co1−xFex alloy nanowires with 40 nm diam and x=0–1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonal-closed-packed structure (hcp) to a face-centered-cubic structure (fcc) in the concentration range

Zero Magnetization States in Electrodeposited Co0.45Fe0.55 Nanowire Arrays

Co0.45Fe0.55 alloy nanowires with 12 to 35 nm diameter and 12 μm length were fabricated by electrodeposition in porous anodic alumina templates. The initial magnetization curves reveal that the zero magnetization state is not unique and is determined by the field history (acdemagnetization process) leading to the zero average moment state. For acdemagnetization processes with the field applied parallel to the nanowire axis, the subsequent magnetization curves suggest that an individual nanowire behaves as a single domain with neighboring nanowires being antiparallel to each other in the zero magnetization state. However, for a demagnetization process with the field applied perpendicular to the nanowires, a different zero magnetization state is created in which the individual nanowires consist of multidomains having opposite axial orientations. These results are consistent with the asymmetric (symmetric) behavior found in the minor hysteresis loops measured after perpendicular (parallel) acdemagnetization on these nanowire arrays

Fabrication and Characterization of Co1−xFex Alloy Nanowires

Co1−xFex alloy nanowires with 40 nm diam and x=0–1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonal-closed-packed structure (hcp) to a face-centered-cubic structure (fcc) in the concentration range

Investigation of The Magnetic Properties in Strontium–Borate Vanadate Glasses

To further elucidate the nature of the valence state of V ions in vanadate glasses,magnetic susceptibility measurements in the temperature range of 5 to 300 K have been performed on a series of vanadium–strontium–borate (V2O5+SrO+B2O3) oxide glasses with V2O5 concentrations greater than 50 mol %. The magnetic susceptibility for these oxide glasses is found to consist of a temperature-independentparamagnetic contribution arising from V2O5 and a Curie–Weiss temperature-dependent contribution associated with magnetic V4+ ions being present in concentrations between 2% and 10% of the total V concentration. The negative Curie–Weiss temperatures in the range of 0 to −2.8 K indicate a weak antiferromagneticinteraction between the V4+ ions. These results are consistent with a glass network structure consisting of VO5 polyhedra in which the V4+ would be predominantly isolated species, and any interactions between the V4+ ions would result from superexchange interactions through V–O–V bonds

Investigation of The Magnetic Properties in Strontium–Borate Vanadate Glasses

To further elucidate the nature of the valence state of V ions in vanadate glasses,magnetic susceptibility measurements in the temperature range of 5 to 300 K have been performed on a series of vanadium–strontium–borate (V2O5+SrO+B2O3) oxide glasses with V2O5 concentrations greater than 50 mol %. The magnetic susceptibility for these oxide glasses is found to consist of a temperature-independentparamagnetic contribution arising from V2O5 and a Curie–Weiss temperature-dependent contribution associated with magnetic V4+ ions being present in concentrations between 2% and 10% of the total V concentration. The negative Curie–Weiss temperatures in the range of 0 to −2.8 K indicate a weak antiferromagneticinteraction between the V4+ ions. These results are consistent with a glass network structure consisting of VO5 polyhedra in which the V4+ would be predominantly isolated species, and any interactions between the V4+ ions would result from superexchange interactions through V–O–V bonds

X-ray Photoelectron Spectroscopy (XPS) and Magnetization Studies of Iron–Vanadium Phosphate Glasses

Vanadium phosphate glasses containing Fe2O3 with the chemical composition [(Fe2O3)x(V2O5)0.6−x(P2O5)0.4], where x=0.00, 0.10, 0.20, 0.25 and 0.30, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility measurements. The core level binding energies of V 2p, Fe 2p, P 2p and P 2s in the Fe2O3–vanadium phosphate glasses have been measured and shifts from the corresponding binding energies measured for V2O5, Fe2O3 and P2O5 powders are accounted for by changes in the next-nearest neighbor environment of these atoms in the P4O10 local structure. The O 1s spectra for the glasses are single, symmetric peaks arising from nearly 95% of the oxygen sites being occupied by non-bridging oxygen atoms. In addition, the broadened V 2p3/2 and Fe 2p3/2 spectra for the glass samples are decomposed into two peaks that are associated with the presence of V5+ and V4+ and Fe3+ and Fe2+, respectively. The magnetic susceptibility data appear to follow a Curie–Weiss behavior (χ=C/(T−θ)) for temperatures above ∼15 K with negative paramagnetic Curie temperatures indicative of antiferromagnetic interactions between the magnetic Fe3+, Fe2+ and V4+ ions. The experimentally determined Curie constants from the susceptibility data are in good agreement with the calculated values based on the Fe3+, Fe2+ and V4+ concentrations determined from the XPS analyses. Other qualitative features in the magnetic susceptibility results can be explained in terms of the formation of various magnetic clusters (single, dimer and trimer) with the introduction of the magnetic ions onto the P sites of the P4O10 structure