46 research outputs found
Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy
The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too
Electronic structure and properties of (TiZrNbCu)_1-xNi_x high entropy amorphous alloys
A comprehensive study of selected properties of four (TiZrNbCu)_1-xNi_x (x
\le 0.25) amorphous high entropy alloys (a-HEA) has been performed. The samples
were ribbons about 20 \mum thick and their fully amorphous state was verified
by X-ray diffraction and thermal analysis. The surface morphology, precise
composition and the distribution of components were studied with a Scanning
electron microscope (SEM) with an energy dispersive spectroscopy (EDS)
attachment. The properties selected were the melting temperature (T_m), the low
temperature specific heat (LTSH), the magnetic susceptibility \chi_exp and the
Young^,s modulus (E). Whereas LTSH and \chi_exp were measured for the as-cast
samples, E was measured both for as-cast samples and relaxed samples (after a
short anneal close to the glass transition temperature). The LTSH showed that
the electronic density of states at the Fermi level, N_0(E_F), decreases with
increasing x, whereas the Debye temperature (\theta_D) increases with x. This
is similar to what is observed in binary and ternary amorphous alloys of early
transition metals (TE) with late transition metals (TL) and indicates that
N_0(E_F) is dominated by the d-electrons of the TE. The LTSH also showed the
absence of superconductivity down to 1.8K and indicated the emergence of the
Boson peak above 4K in all alloys.The free-electron like paramagnetic
contribution to \chi_exp also decreases with x, whereas E, like \theta_D,
increases with x, indicating enhanced interatomic bonding on addition of Ni.
The applicability of the rule of mixtures to these and other similar HEAs is
briefly discussed
ECONOMIC ANALYSIS OF FRESHWATER FISH PRODUCTION IN THE REPUBLIC OF SERBIA
The authors present the basic characteristics of the fish production in the Republic of Serbia. In the case of the fishpond "OZZ Despotovo", in the municipality of Bačka Palanka, the main economic indicators achieved in the production of freshwater fish (carp, grass carp, silver carp, catfish) are analyzed. The observed production requires very high investment per unit area (€ 4,381.39 ha-1). Despite significant investment, achieved economic results are relatively modest (the contribution margin € 892.15 ha-1; the cost-effectiveness ratio 1.09; the profit rate 8.10%). System support of country in the modernization of existing fishponds and raising the new ones, it can significantly contribute to the improvement of production and economic results in the fish production on the territory of the Republic of Serbia
Magnetic excitations and electronic interactions in SrCuTeO: a spin-1/2 square lattice Heisenberg antiferromagnet
SrCuTeO presents an opportunity for exploring low-dimensional
magnetism on a square lattice of Cu ions. We employ ab initio
multi-reference configuration interaction calculations to unravel the Cu
electronic structure and to evaluate exchange interactions in SrCuTeO.
The latter results are validated by inelastic neutron scattering using linear
spin-wave theory and series-expansion corrections for quantum effects to
extract true coupling parameters. Using this methodology, which is quite
general, we demonstrate that SrCuTeO is an almost realization of a
nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling
of 7.18(5) meV.Comment: 10 pages, 7 figure
Ferromagnetism in Co7(TeO3)4Br6: A byproduct of complex antiferromagnetic order and single-ion anisotropy
Pronounced anisotropy of magnetic properties and complex magnetic order of a
new oxi-halide compound Co7(TeO3)4Br6 has been investigated by powder and
single crystal neutron diffraction, magnetization and ac susceptibility
techniques. Anisotropy of susceptibility extends far into the paramagnetic
temperature range. A principal source of anisotropy are anisotropic properties
of the involved octahedrally coordinated single Co(2+) ions, as confirmed by
angular-overlap-model calculations presented in this work. Incommensurate
antiferromagnetic order sets in at TN=34 K. Propagation vector is strongly
temperature dependent reaching k1=(0.9458(6), 0, 0.6026(5)) at 30 K. A
transition to a ferrimagnetic structure with k2=0 takes place at TC=27 K.
Magnetically ordered phase is characterized by very unusual anisotropy as well:
while M-H scans along b-axis reveals spectacularly rectangular but otherwise
standard ferromagnetic hysteresis loops, M-H studies along other two principal
axes are perfectly reversible, revealing very sharp spin flop (or spin flip)
transitions, like in a standard antiferromagnet (or metamagnet). Altogether,
the observed magnetic phenomenology is interpreted as an evidence of competing
magnetic interactions permeating the system, first of all of the single ion
anisotropy energy and the exchange interactions. Different coordinations of the
Co(2+)-ions involved in the low-symmetry C2/c structure of Co7(TeO3)4Br6 render
the exchange-interaction network very complex by itself. Temperature dependent
changes in the magnetic structure, together with an abrupt emergence of a
ferromagnetic component, are ascribed to continual spin reorientations
described by a multi-component, but yet unknown, spin Hamiltonian.Comment: 12 pages, 13 figures; submitted to PR
Enhanced superconductivity in Hf-base metallic glasses
Systematic study of electrical resistivity of Hf_{100-x}Fe_x (x=20,25),
Hf_{100-x}Cu_x (x=30,40,50), and Ti_{65}Cu_{35} metallic glasses has been done
in the temperature range 0.3 K - 290 K, and in magnetic fields B <= 5 T. All
Hf-base alloys are superconducting with T_c >= 0.44 K, which is well above T_c
of pure crystalline Hf (0.13 K). From the initial slopes of the upper critical
fields, (dH_{c2}/dT)_{T_c}, and resistivities we determined the dressed
electronic densities of states, N_{\gamma}(E_F), for all alloys. Both T_c and
N_{\gamma}(E_F) decrease with increasing x (Fe and Cu content). The results are
compared with those for corresponding Zr-base metallic glasses and
ion-implanted Hf films.Comment: 9 pages, 4 figures, 1 tabl