共查询到20条相似文献,搜索用时 109 毫秒
1.
J. A. De Toro J. P. Andr��s J. A. Gonz��lez J. M. Riveiro M. Estrader A. L��pez�COrtega I. Tsiaoussis N. Frangis J. Nogu��s 《Journal of nanoparticle research》2011,13(10):4583-4590
The magnetic properties of diluted films composed of nanocomposite Co-CoO nanoparticles (of ~8 nm diameter) dispersed in a Cu matrix have been investigated. The nanoparticles were formed in an aggregation chamber by sputtering at different Ar/O2 partial pressures (0?C0.015). The exchange-bias properties appear to be insensitive to the amount of O2 during their formation. However, the temperature dependence of the magnetization, M(T), exhibits two different contributions with relative intensities that correlate with the amount of O2. The magnetic results imply that two types of particles are formed, nanocomposite Co-CoO (determining the exchange-bias) and pure CoO, as confirmed by transmission electron microscopy observations. Importantly, as the O2 partial pressure during the sputtering is raised the number of nanocomposite Co-CoO nanoparticles (exhibiting exchange-bias properties) is reduced and, consequently, there is an increase in the relative amount of pure, antiferromagnetic CoO particles. 相似文献
2.
Exchange biasing was studied in an exchange-spring system
consisting of two ferrimagnetic films with different coercivity.
Magnetite and Co-Fe ferrite were chosen as the soft and hard
magnetic bilayer components, respectively. The samples were
epitaxially grown on MgO single crystal substrates by pulsed laser
deposition. The exchange-bias field was investigated as a function
of system size and shape, magnetic field direction and
magnetization reversal in the hard layer. A clear dependence of
the exchange-bias field on the sample size and shape was
found. This was attributed to an interplay between exchange and
dipolar energies. Micromagnetic simulations agree with
the experimental results. 相似文献
3.
In an exchange-bias system, the barriers with intrinsic potential energy may be asymmetric due to unidirectional anisotropy. Based on the Stoner-Wohlfarth model, we show that the asymmetric barriers may lead to four kinds of dynamical process underlying the hysteresis-loop measurement. These kinds of dynamical processes are different in a topology-like property, which can be controlled by the orientation of the external field. In our study, a new analysis approach has been proposed to reveal the dynamical behaviors of magnetization reversal. With this approach, coercivity, exchange-bias field, and asymmetry of hysteresis loops can be quantitatively obtained. 相似文献
4.
A. Masseboeuf C. Gatel P. Bayle-Guillemaud B. Viala 《Journal of magnetism and magnetic materials》2009,321(19):3080-3083
Lorentz transmission electron microscopy (LTEM) combined with in-situ magnetizing experiments is a powerful tool for the investigation of the magnetization of the reversal process at the micron scale. We have implemented this tool on a conventional transmission electron microscope (TEM) to study the exchange anisotropy of a polycrystalline Co35Fe65/NiMn bilayer. Semi-quantitative maps of the magnetic induction were obtained at different field values by the differential phase contrast (DPC) technique adapted for a TEM (SIDPC). The hysteresis loop of the bilayer has been calculated from the relative intensity of magnetic maps. The curve shows the appearance of an exchange-bias field reveals with two distinct reversal modes of the magnetization: the first path corresponds to a reversal by wall propagation when the applied field is parallel to the anisotropy direction whereas the second is a reversal by coherent rotation of magnetic moments when the field is applied antiparallel to unidirectional anisotropy direction. 相似文献
5.
Tomasz Błlachowicz 《Central European Journal of Physics》2006,4(3):331-340
The existence of minority spins, opposite to the perpendicular exchange bias, and majority spins aligned with this bias, and
the dependence of the perpendicular exchange-bias field on the imprint effect, caused by the partially covering spacer at
the ferromagnetic/antiferromagnetic (FM/AFM) interface, have been studied using Ising-type simulations. The present investigation
suggests that the main factors influencing this phenomenon were dependent on the FM/AFM interface morphology, the balance
between FM/AFM coupling and the FM-spins coupling, and the numerical balance between minority and majority spins. It was also
determined that the imprint phenomenon can be used to enhance the perpendicular exchange-bias for small partial insertions
at the FM/AFM interface.
An erratum to this article is available at. 相似文献
6.
In Co/CoO nanostructures, of dimensions l×3l, at small Co thickness (≈6,10 nm), a strong increase in the bias field and the associated coercive field are found as the nanostructure size is reduced from l=120 nm to l=30 nm. This property indicates that the characteristic length D(AF) within the antiferromagnet which governs exchange-bias effects is the nanostructure size. By contrast, at larger Co thickness (≈23 nm), the exchange-bias field does not depend on the nanostructure size, implying that D(AF) is smaller than the nanostructure size. The results are discussed in the framework of the Malozemoff model, taking into account that the coupling between CoO grains is weak. Exchange bias is dominated either by coupling within the antiferromagnetic layer (6- and 10-nm-thick Co samples) or by ferromagnetic-antiferromagnetic interfacial coupling (23-nm-thick Co sample). 相似文献
7.
Bakhmet’ev M. V. Talantsev A. D. Morgunov R. B. 《Journal of Experimental and Theoretical Physics》2021,132(5):852-864
Journal of Experimental and Theoretical Physics - The NiFe/Cu/IrMn heterostructures with a variable number of interlayer Cu atoms exhibit a sharp change in the exchange-bias field, the coercive... 相似文献
8.
Thermodynamic stability conditions for nanoparticles (resulting from non-negativity of the second variation of the free energy)
have been analyzed for two cases: (i) a nonvolatile nanosized particle with the size-dependent surface tension; (ii) the limiting
case of larger objects when the surface tension takes its macroscopic value. It has been shown that the mechanical stability
of a nanoparticle, i.e. its stability relative to the volume fluctuations, is defined by an interplay between the excess (“surface”)
free energy and the volumetric elastic energy. According to the results obtained, noble gas clusters and metal nanoparticles
satisfy the mechanical stability condition. At the same time, water nanodrops, as well as nanoparticles presented by nonpolar
organic molecules, correspond to the stability limit. Among the investigated systems, the stability condition is not carried
out for n-Pentane clusters. 相似文献
9.
Fe/Mn multilayers were grown by means of a molecular beam epitaxy system onto quartz substrates changing the thickness of the elemental layers. A spontaneous unidirectional anisotropy develops for thickness of Fe or Mn layer of about 35 Å. Since the samples were no subjected to field cooling treatments during or after the growth, this kind of anisotropy can be explained considering besides the exchange coupling at the Fe/Mn interface, the structural disorder due to dislocations and defects. In effect, the appearance and strength of the exchange-bias field are depending on the surface roughness of the samples and are significantly enhanced by the formation of a structure constituted by islands showing a snake-like morphology. The fitting of the angular dependence of the exchange-bias field indicates that the associated anisotropy is due to the superposition of two contributions, the principal one with unidirectional symmetry and the other showing uniaxial characteristics. 相似文献
10.
Krzysztof Drozdowicz Barbara Gabańska Andrzej Igielski Ewa Krynicka Urszula Woźnicka 《Central European Journal of Physics》2003,1(2):210-234
The structure of a heterogeneous system influences diffusion of thermal neutrons. The thermal-neutron absorption in grained
media is considered in the paper. A simple theory is presented for a two-component medium treated as grains embedded in the
matrix or as a system built of two types of grains (of strongly differing absorption cross-sections). A grain parameter is
defined as the ratio of the effective macroscopic absorption cross-section of the heterogeneous medium to the absorption cross-section
of the corresponding homogeneous medium (consisting of the same components in the same proportions). The grain parameter depends
on the ratio of the absorption cross-sections and contributions of the components and on the size of grains. The theoretical
approach has been verified in experiments on prepared dedicated models which have kept required geometrical and physical conditions
(silver grains distributed regularly in Plexiglas). The effective absorption cross-sections have been measured and compared
with the results of calculations. A very good agreement has been observed. In certain cases the differences between the absorption
in the heterogeneous and homogeneous media are very significant. A validity of an extension of the theoretical model on natural,
two-component, heterogeneous mixtures has been tested experimentally. Aqueous solutions of boric acid have been used as the
strongly absorbing component. Fine- and coarse-grained pure silicon has been used as the second component with well-defined
thermal-neutron parameters. Small and large grains of diabase have been used as the second natural component. The theoretical
predictions have been confirmed in these experiments. 相似文献
11.
Bartolo Luque 《Central European Journal of Physics》2003,1(3):516-555
This work is a tutorial in Molecular Evolution from the point of view of Physics. We discuss Eigen's model, a link between
evolutionary theory and physics. We will begin by assuming the existence of (marco) molecules or replicators with the template
property, that is, the capacity to self-replicate. According to this assumption, information will be randomly generated and
destroyed by mutations in the code (i.e., errors in the copying process) and new bits of information will be fixed (made stable)
by the existence of an external pressure on the system (i.e., selection), and the ability of the molecules to replicate themselves.
Our aim is to build a model in order to describe molecular evolution from as general a standpoint as possible. As we will
see, even very simple models from the theoretical point of view will have surprisingly deep consequences. 相似文献
12.
Ivan Banik 《Central European Journal of Physics》2005,3(2):270-302
Barrier model of a non-crystalline semiconductor is described in this article. The most important optical phenomena, which
are typical for this group of materials, are explained on the base of this model. The model assumes that in non-crystalline
semiconductors the potential barriers exist, which separate certain microscopic areas from each other, assuming barriers possess
a parabolic profile. This conception explains the rise of exponential tails of optical absorption at the end of optical edge
as well as electroabsorption, photoelectric conductivity, photoluminescence, and others. Using this model, many electric transport
properties of non-crystalline semiconductors can be explained successfully. 相似文献
13.
The state of technological systems, such as reactions in a confined volume, are usually monitored with sensors within as well
as outside the volume. To achieve the level of precision required by regulators, these data often need to be supplemented
with the solution to a mathematical model of the process. The present work addresses an observed, and until now unexplained,
convergence problem in the iterative solution in the application of the finite element method to boundary value problems.
We use point group theory to clarify the cause of the non-convergence, and give rule problems. We use the appropriate and
consistent orders of approximation on the boundary and within the volume so as to avoid non-convergence. 相似文献
14.
K. N. Korostik 《Journal of Applied Spectroscopy》1998,65(1):55-61
The influence of stimulated emission delay, dynamic shift in generation frequency, residual charge effect, timing jitter of
the radiation and excitation regime of an injection laser, as well as of dispersion in a fiber light guide on the data-internal
storage time in an electrooptical contour is investigated. It is found that the storage duration of an interval depends strongly
on the lifetime of nonequilibrium charge carriers, the simultaneous effect of a residual charge and jitter in an injection
laser, as well as on the dc bias current of the laser.
Belarusian State University, 4. F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 65, No. 1, pp. 56–61, January–February, 1998. 相似文献
15.
A finite Heisenberg magnetic ring with an arbitrary single-node spin and two spin deviations from the ferromagnetic saturation
is considered as the system of two Bethe pseudoparticles. The set of all relevant magnetic configurations spans a surface
which can be recognised as a Mőbius strip. The dynamics of the system imposes the double twist of all regular orbits of the
translation symmetry group. 相似文献
16.
Volodymyr Krasnoholovets 《Central European Journal of Physics》2004,2(4):698-708
Using the methods of statistical mechanics we have shown that a homogeneous water network is unstable and spontaneously disintegrates
to the nonhomogeneous state (i.e. peculiar clusters), which can be treated as an ordinary state of liquid water. The major
peculiarity of the concept is that it separates the paired potential into two independent components—the attractive potential
and the repulsive one, which in turn should feature a very different dependence on the distance from the particle (a water
molecule in the present case). We choose the interaction potential as a combination of the ionic crystal potential and the
vibratory potential associated with the elastic properties of the water system as a whole. The number ℵ of water molecules
that enters a cluster is calculated as a function of several parameters, such as the dielectric constant, the mass of a water
molecule, the distance between nearest molecules, and the vibrations of nearest molecules in their nodes. The number of H2O molecules that comprise a cluster is estimated as about ℵ ≈ 900, which agrees with the available experimental data.
Presented at the 2nd International Conference “Physics of Liquid Matter: Modern Problems” (September 2003, Kyiv, Ukraine) 相似文献
17.
Solid-solution formation in binary aluminium-based alloys is due essentially to the combined effects of the size and valence of solvent and solute atoms, as expected by the four Hume-Rothery rules. The lattice parameter of aluminium in the solid solution of the sputtered Al?Fe films is [Al-a (Å)=4.052?6.6×10?3Y]. The increasing and decreasing evolution of the lattice parameter of copper [Cu-a (Å)=3.612+1.8×10?3Z] and aluminium [Al-a (Å)=4.048?1.6×10?3X] in the sputtered Al-1.8 to 92.5 at. % Cu films is a result of the difference in size between the aluminium and copper atoms. The low solubility of copper in aluminium (<1.8 at % Cu) is due to the valences of solvent and solute atoms in contrast with other sputtered films prepared under similar conditions, such as Al?Mg (20 at. % Mg), Al?Ti (27 at. % Ti), Al?Cr (5at. % Cr) and Al?Fe (5.5 at. % Fe) where the solubility is due to the difference in size. 相似文献
18.
The formation of Saturn and its disk is simulated using a new N-body self-gravitational model. It is demonstrated that the
formation of the disk and the planet is the result of gravitational contraction of a slowly rotated particle cloud that have
a shape of slightly deformed sphere. The sphere was flattened by a coefficient of 0.8 along the axis of rotation. During the
gravitational contraction, the major part of the cloud transformed into a planet and a minor part transformed into a disk.
The thin structured disk is a result of the electromagnetic interaction in which the magnetic forces acting on charged particles
of the cloud originate in the core of the planet. The simulation program gives such parameters of Saturn as the escape velocity
of about 35 km/s at the surface, density, rotational velocities of the rings and temperature distribution. 相似文献
19.
Xiaomin Wang Hong Zhou Kangsheng Chen 《International Journal of Infrared and Millimeter Waves》1993,14(6):1229-1236
A new kind of mm-wave cusptron tube with anti-coaxial-magnetron-type wall structure is proposed. The dispersion equation of its RF circuit and the coupled resonant interaction equations of electrons with the waveguide mode fields are derived. A numerical simulation of the non-linear interaction process is carried out. It is found that in the cusptron tube proposed here, there may exists a new energy conversion mechanism with higher efficiency than that of conventional cusptron. Numerical results also show that the saturation efficiency for this mechanism is not sensitive to the applied dc magnetic field Bo. The saturation efficiency as the function of operation parameters, such as magnetic field Bo and electron voltage V, and the geometry of waveguide circuit is numerically illustrated. From that, the optimized design parameters for anti-coaxial-magnetron-type cusptron can be determined. 相似文献
20.
Numerical simulation of industrial crystal growth is difficult due to its multidisciplinary nature and the complex geometry
of the real-life growth equipment. An attempt is made to itemize physical phenomena dominant in the different methods for
growth of bulk crystals from the melt and the vapor phase as well as to review corresponding numerical approaches. Academic
research and industrial applications are compared. Development of a computational engine and a graphic user interface of the
industry-oriented codes is discussed. A simulator for the entire growth process of bulk crystals by sublimation method is
described. 相似文献