Ferromagnetic resonance investigation of nanocrystalline FeCuNbSiB

An elaborate line-shape analysis of the ferromagnetic resonance (FMR) spectra taken in the temperature range 100 K to 350 K on amorphous FeCuNbSiB alloys before and after nanocrystallizing them reveals that in the nanocrystalline state, (i) spin wave stiffness (D) is enhanced while the saturation magnetization, MS, is reduced, (ii) both the 'in-plane' anisotropy field, HK, as well as the FMR line-width scale with MS, (iii) the single-ion anisotropy of spin-orbit plus crystal field origin dominates over the twoion anisotropy of dipolar origin and (iv) multi-magnon scattering contributions to FMR line-width become important in some cases

Microwave spin resonance investigation on the effect of the post-processing annealing of CoFe2O4 nanoparticles

A novel investigation on the finite-size effects on the spin resonance properties of cobalt ferrite (CoFe2O4) nanoparticles has been performed using a room temperature ferromagnetic resonance (FMR) technique. A single broad spectrum was obtained for the CoFe2O4 nanoparticle samples, which indicated that all the samples were showing ferromagnetic characteristics. An asymmetric FMR line shape with a hefty trailing section was obtained due to the high magneto-crystalline anisotropy in CoFe2O4 nanoparticles, which changed with the size distribution. The resonance field for the samples shifted to a higher value due to the increase in the magneto-crystalline anisotropy in the CoFe2O4 nanoparticles with an increase in size. A systematic change in the resonance field and line width was observed with the change in the size distribution of the particles. Initially, it decreased with an increase in the size of the particles and increased after the critical size range. The critical size range is the imprint of the shift of the magnetic domain from a single domain to multi domain. The line width increased at higher annealing temperatures due to the enhancement in the dipole-dipole interaction, which led to a higher spin concentration as well as magneto-crystalline anisotropy. Furthermore, the saturation magnetization (M-s) as well as 'M-r/M-s' increased from 37.7 to 71.4 emu g(-1) and 0.06 to 0.31, respectively. The highest coercivity (750.9 Oe) and anisotropy constant (4.62 x 10(4) erg cm(-3)) were found for the sample annealed at 700 degrees C, which can be corroborated by the literature as the critical annealing temperature at which CoFe2O4 nanoparticles shift from single domain nanoparticles to multi-domain nanoparticles. Post-processing annealing is critical in advanced processing techniques and spin dynamics plays a vital role in various interdisciplinary areas of applications

Finite-size scaling in band ferromagnets with non-universal critical behavior

The ultra-high sensitivity of the ferromagnetic resonance (FMR) technique has been fully exploited to study the finite-size effects in the critical region near the ferromagnetic to paramagnetic phase transition in Cr75-xFe25+x(x = 0, 5) thin films of high structural and magnetic quality. Conclusive experimental evidence is provided for the validity of finite-size scaling. Irrespective of the film thickness and composition, the critical exponents β, γ and ν for spontaneous magnetization, initial magnetic susceptibility and spin-spin correlation length retain their bulk values so that no dimensionality crossover occurs within the film thickness range covered in the FMR experiments. The present results indicate that (i) like Cr75-xFe25+x, the previously studied Fe, Co, Ni, and CoNi3 thin films behave as itinerant-electron (band) ferromagnets in which the isotropic long-range interactions between spins decay as J(r)~r-(d+σ) (σ>0), and (ii) the lattice dimensionality d, spin dimensionality m, and range of spin-spin interactions (via the material-specific parameter s) decide the (non-universal) values of the critical exponents

Trapping and Injecting Single DomainWalls in Magnetic Wire by Local Fields

single domain wall (DW) moves at linearly increasing velocity under an increasing homogeneous drive magnetic field. Present experiments show that the DW is braked and finally trapped at a given position when an additional antiparallel local magnetic field is applied. That position and its velocity are further controlled by suitable tuning of the local field. In turn, the parallel local field of small amplitude does not significantly affect the effective wall speed at long distance, although it generates tail-to-tail and head-to-head pairs of walls moving along opposite directions when that field is strong enough.Spanish Ministry of Science and Innovation, Project No. MAT2010-20798-C05-01. G. A. Basheed acknowledges the postdoctoral grant from the Spanish MICINNPeer reviewe

Structural and mossbauer effect investigations of amorphous FeCuNbSiB alloys nanocrystallized (VITROPERM) in magnetic field

Melt-spun amorphous ribbons of nominal composition Fe73Cu1Nb3Si16B7, annealed at 560-580 °C for 1 hour in a magnetic field (H) applied along the width in the ribbon plane, develop uniaxial magnetic anisotropy with easy axis along H and exhibit several novel attributes. The samples labelled as S20 and S150 are nanocomposites consisting of ferromagnetic nanocrystalline grains (volume fraction ≈ 84% and 81%) of mean size d = 13(2) nm embedded in a ferromagnetic amorphous matrix and possess a magnetic permeability as large as 20,000 and 150,000, respectively. While nearly 55% of the nanocrystalline grains have a cubic DO3Fe3Si-like structure with actual Si concentration of about 22 at.%, the remaining 45% nanocrystalline grains have tetragonal Fe3B and hexagonal Fe2Si structure. Since the crystalline volume fraction of Fe3B and Fe2Si nanocrystals is more in the sample S20, this sample exhibits stronger local magnetic anisotropy and hence lower permeability

Magnetodielectric coupling in epitaxial Nd2CoMnO6 thin films with double perovskite structure

Double perovskite Nd2CoMnO6 thin films have been grown epitaxially on SrTiO3 substrates using pulsed laser deposition and their structural, magnetic, and dielectric properties were investigated. Temperature dependent dielectric (epsilon) constant is measured in the frequency range between 1 kHz and 1MHz under applied magnetic fields up to 0.5 kOe. The dielectric constant exhibits an anomaly near to the Curie temperature which is independent of magnetic field and can be corroborated with a loop opening temperature in zero-field-cooled and field-cooled magnetization measurements. While, a linear relationship between magnetodielectric constant, delta epsilon(MD), and M-2(magnetization) in the paramagnetic to ferromagnetic regime proves magnetodielectric coupling between ferroelectric and ferromagnetic orders in this single-phase perovskite system

Evidence for new crystalline phases formed during early stages of crystallization of amorphous FeCuNbSiB alloys

Amorphous FeCuNbSiB alloys with composition near Fe73.5Cu1Nb3Si13.5B9 (the well-studied FINEMET alloy) were annealed at 520 °C for different durations of time, tA, varying from 3 to 20 min. Detailed investigation of the structure and composition of crystalline phases formed during the initial stages of crystallization in these alloys using techniques such as x-ray diffraction, Mossbauer spectroscopy, scanning electron microscopy, atomic force microscopy and energy dispersive absorption of x-rays, revealed the following. New crystalline phases, tetragonal Fe3B and hexagonal Fe2Si, not reported previously, exist in all the nanocrystalline alloys in question in contrast to the well-documented cubic Fe-Si phase with the DO3 structure which coexists with the Fe3B and Fe2Si phases in some compositions only. The crystallization of Fe3B and Fe2Si nanocrystalline grains starts at the surface of the ribbons and then proceeds to the bulk whereas the crystallization of DO3 Fe-Si gets initiated within the bulk. The average size of the nanocrystalline grains of the Fe3B and Fe2Si and cubic DO3 Fe-Si structures in the residual amorphous matrix is around 20 nm but their volume fractions are as low as ≈ 5%, 10%, and 7%, respectively. The cubic Fe-Si nanocrystals of the DO3 structure have a silicon concentration in the range 15-20 at.%. The magnetic moments in the amorphous precursor point, on average, are 40° out of the ribbon plane while in the nanocrystalline alloys this angle varies between 2° and 19° depending on the Fe concentration

Resonant microwave absorption determination of characteristic magnetic length in magnetic-field-annealed Vitroperm

The first direct resonant microwave absorption determination of the thermal renormalization of exchange stiffness, average magnetic anisotropy constant, and characteristic magnetic length in “field-annealed” Vitroperm samples with an initial magnetic permeability of μi = 20 000 and 150 000 has been presented and discussed

Origin of 'in-plane' and 'out-of-plane' magnetic anisotropies in as-deposited and annealed CoFeB ferromagnetic thin films

A detailed comparative Ferromagnetic resonance study of pulsed laser deposited Co40Fe40B20 thin films, before and after annealing, was under taken. The dependence of resonance field (H-res) and peak-to-peak linewidth (Delta H-pp) on film thickness, annealing temperature, and magnetic field orientation is examined. 'In-plane' (IP) and 'out-of-plane' (OP) angular dependence of the resonance fields, (IP:H-res(psi); OP:H-res(alpha)), were measured at T = 150 and 295K for the as deposited (as-) to annealed (an-) thin film samples to determine IP (H-K(parallel to)) and OP (H-K(perpendicular to)) uniaxial anisotropy fields. Variation of H-res(psi) and H-res(alpha) on sample geometry demonstrate that the uniaxial magnetic anisotropy is present in as-and an-thin films of Co40Fe40B20. The effective magnetic anisotropy (K-u(eff)) increases after nanocrystallization in CoFeB films indicates that the exchange interactions are unable to average out the local-magnetocrystalline anisotropy of the nanocrystalline grains and thereby lead to magnetic hardening in the early stages of crystallization

Synthesis and Characterizations of (In0.90Sn0.05Ni0.05)(2)O-3 Nanoparticles Using Solid State Reaction Method

ITO (In0.95Sn0.05)(2)O-3 and Ni doped ITO (In0.90Sn0.05Ni0.05)(2)O-3 nanoparticles (NPs) were synthesized by solid state reaction method and subjected to study their structural, optical and magnetic properties. The NPs had a size distribution in the range of 40 nm and were identified as the bcc cubic In2O3 by X-ray diffraction (XRD). Optical properties of the samples were studies using UV-Vis-NIR spectrophotometer. Magnetic measurements were carried out at room temperature and at 100 K using vibrating sample magnetometer and found that the ITO nanoparticles were ferromagnetic in nature at room temperature. The strength of the magnetization decreased in ITO nanoparticles when the magnetic measurements carried out at 100 K