Search results for "Anisotropy"
showing 10 items of 912 documents
Thin epitaxial films of the Heusler compound
2005
Abstract We prepared thin films of the Heusler compound Co 2 Cr 0.6 Fe 0.4 Al with the B2 structure on a-plane (1 1 2 ¯ 0) Al 2 O 3 by sputtering. Films grown at high temperatures ( T ⩾ 600 ∘ C ) on Al 2 O 3 are fully epitaxial with the (1 1 0) and (1 1 ¯ 0) planes of the film parallel to the (1 1 2 ¯ 0) and (0 0 0 1) planes of the substrate, respectively. These epitaxial films possess a higher surface roughness than films grown at room temperature. The films show nearly rectangular hysteresis loops with coercive fields of the order of 10 mT. Magnetooptical Kerr measurements show an in-plane anisotropy of the magnetization with the easy axis in { 0 0 1 } direction. Hall measurements s…
Thermal fluctuations and longitudinal relaxation of single-domain magnetic particles at elevated temperatures
2004
We present numerical and analytical results for the swiching times of magnetic nanoparticles with uniaxial anisotropy at elevated temperatures, including the vicinity of T_c. The consideration is based in the Landau-Lifshitz-Bloch equation that includes the relaxation of the magnetization magnitude M. The resulting switching times are shorter than those following from the naive Landau-Lifshitz equation due to (i) additional barrier lowering because of the reduction of M at the barrier and (ii) critical divergence of the damping parameters.
Phonon dispersion in GaN/AlN non‐polar quantum wells: confinement and anisotropy
2007
We have calculated the phonon dispersion relations in a non-polar GaN/AlN quantum well within the dielectric continuum model and making use of Loudon's model of uniaxial crystals. Due to the strong in-plane anisotropy of this orientation, we have found that in general ordinary and extraordinary phonons are not decoupled. In this work we analyze the conditions for the occurrence of interface modes. In these novel heterostructures there is an added dependence of the phonon dispersion on the orientation of the in-plane phonon wavevector, which allows the existence of interface phonons at energies forbidden in the better known polar structures. Under particular circumstances the vibrations exci…
Structural Principles and Thermoelectric Properties of Polytypic Group 14 Clathrate-II Frameworks
2013
We have investigated the structural principles and thermoelectric properties of polytypic group 14 clathrate-II frameworks using quantum chemical methods. The experimentally known cubic 3C polytype was found to be the energetically most favorable framework, but the studied hexagonal polytypes (2 H, 4 H, 6 H, 8 H, 10 H) lie energetically close to it. In the case of germanium, the energy difference between the 3C and 6H clathrate-II polytypes is ten times smaller than the difference between the experimentally known 3C-Ge (α-Ge) and 4H-Ge polytypes. The thermoelectric properties of guest-occupied clathrate-II structures were investigated for compositions Na-Rb-Ga-Ge and Ge-As-I. The clathrate-…
Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization
2014
Yttrium iron garnet (YIG, Y [subscript 3]Fe[subscript 5]O[subscript 12]) films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd[subscript 3]Ga[subscript 5]O[subscript 12]) substrates with (100) orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe), near-bulk room temperature saturation moments (∼135 emu cm[superscript −3]), in-plane easy axis, and damping parameters as low as 2.2 × 10[superscript −4]. These high quality YIG thin films are useful in the investigation…
A [Cr2Ni] coordination polymer: slow relaxation of magnetization in quasi-one-dimensional ferromagnetic chains
2018
The reaction of [Cr3IIIO(OAc)6(H2O)3]NO3·AcOH with 2-hydroxynaphthaldehyde, 2-amino-isobutyric acid and NiCl2·6H2O in MeOH, under basic and solvothermal conditions, led to the formation of the quasi-1D coordination polymer {[CrIII2NiII(L)4(MeOH)2]}n (where L = the dianion of the Schiff base between 2-hydroxynaphthaldehyde and 2-amino-isobutyric acid), which behaves as a ferromagnetic chain, displaying slow relaxation of magnetization.
Ferromagnetic and paramagnetic magnetization of implanted GaN:Ho,Tb,Sm,Tm films
2015
The SQUID magnetic measurements were performed on the GaN films prepared by metal-organic vapour phase epitaxy and implanted by Tb3+, Tm3+, Sm3+, and Ho3+ ions. The sapphire substrate was checked by the electron paramagnetic resonance method which showed a content of Cr3+ and Fe3+ impurities. The samples 5 × 5 mm2 were positioned in the classical straws and within an estimated accuracy of 10−6 emu, no ferromagnetic moment was detected in the temperature region of 2–300 K. The paramagnetic magnetization was studied for parallel and perpendicular orientation. In the case of GaN:Tb sample, at T = 2 K, a pronounced anisotropy with the easy axis perpendicular to the film was observed which can b…
On the influence of orientation upon the mechanical behavior of oakwood in a general state of stress
1995
Influence of orientation upon the mechanical behavior of oakwood has been studied. The approach within anisotropic medias mechanics supposes oakwood orthotropic with three orthogonal symmetry axes considered to be the privileged directions that occur during the growth of oaktree. Experimental tests consisted in compression tests under confining pressure realized on cylindric samples of oakwood chopped in 18 privileged directions. Although well known in solid mechanics, our approach is original in mechanics and rheology of wood. The obtained results disclosed an influence of the confining pressure upon the mechanical behavior of oakwood and its anisotropy including different types of anisotr…
Hygroexpansivity of anisotropic sheets
2015
Dimensional instability, more particularly its component hygroexpansivity, may cause problems in process or end-use situations in which paper or board is in contact with water or subject to changes in ambient relative humidity. Misregistration in printing, curl during copying and calender wrinkles are examples of such defects. In this paper, the in-plane hygroexpansivity of oriented laboratory sheets with different pulps and dried both freely and under restraint is studied. A linear relationship between the drying shrinkage and hygroexpansion coefficient of freely dried laboratory sheets having different fiber orientation anisotropies, was observed. Regardless of both the measurement direct…
Nanodroplets on a solid plane: wetting and spreading in a Monte Carlo simulation
2002
Abstract The wetting behavior and spreading dynamics of small polymer melt droplets in the course of transition from partial to complete wetting conditions on a flat structureless solid substrate have been studied by dynamic Monte Carlo simulation. From the density profiles of the drops we determine the contact angles at varying strength of the van der Waals surface forces in the whole interval of partial wetting. The validity of Young's equation is then tested whereby the surface tension of the melt/vapor interface is derived independently from interfacial fluctuation analysis, and the surface free energy of the melt at the substrate—from the anisotropy of the local pressure at the wall. T…