Abstract
Indium-substituted strontium hexaferrites were prepared by the conventional solid-phase reaction method. Neutron diffraction patterns were obtained at room temperature and analyzed using the ...Rietveld methods. A linear dependence of the unit cell parameters is found. In
3+
cations are located mainly in octahedral positions of 4f
VI
and 12 k. The average crystallite size varies within 0.84–0.65 μm. With increasing substitution, the T
C
Curie temperature decreases monotonically down to ~ 520 K. ZFC and FC measurements showed a frustrated state. Upon substitution, the average and maximum sizes of ferrimagnetic clusters change in the opposite direction. The M
r
remanent magnetization decreases down to ~ 20.2 emu/g at room temperature. The M
s
spontaneous magnetization and the k
eff
effective magnetocrystalline anisotropy constant are determined. With increasing substitution, the maximum of the ε
/
real part of permittivity decreases in magnitude from ~ 3.3 to ~ 1.9 and shifts towards low frequencies from ~ 45.5 GHz to ~ 37.4 GHz. The maximum of the tg(α) dielectric loss tangent decreases from ~ 1.0 to ~ 0.7 and shifts towards low frequencies from ~ 40.6 GHz to ~ 37.3 GHz. The low-frequency maximum of the μ
/
real part of permeability decreases from ~ 1.8 to ~ 0.9 and slightly shifts towards high frequencies up to ~ 34.7 GHz. The maximum of the tg(δ) magnetic loss tangent decreases from ~ 0.7 to ~ 0.5 and shifts slightly towards low frequencies from ~ 40.5 GHz to ~ 37.7 GHz. The discussion of microwave properties is based on the saturation magnetization, natural ferromagnetic resonance and dielectric polarization types.
•In-substituted SrM hexaferrites were synthesized using solid state reactions.•Coexistence of the electrical and magnetic ordering at room temperature was observed.•Formation of the bevelled magnetic ...structure was no detected.•The reason of the ferroelectricity was discussed in the frame of P63mc space group.
The local crystal/magnetic structures of the SrFe12−xInxO19 solid solutions (x = 0.1; 0.3; 0.6 and 1.2) were investigated using neutron powder diffraction. The measurements of the electric polarization for all investigated samples were carried out as a function of the external electric field. The presence of the ferroelectric and ferromagnetic ordering (dual ferroic ordering) in the SrFe12−xInxO19 hexaferrites at 300 K was found. This appearance contradicts to the conventional opinion describing their crystal structure (centrosymmetric space group P63/mmc (No. 194)). The reason for the existence of a spontaneous polarization (nonzero dipole moment) in the SrFe12−xInxO19 hexaferrites continues controversial. The crystal structure of the hexaferrites was considered both the centrosymmetric P63/mmc and non-centrosymmetric P63mc space groups. This fact made it possible to find a connection between the emerging dipole moment and not equal distortions of the neighbor oxygen polyhedral. The nature description of the nonzero dipole moment formation in a quasi-centrosymmetrical system of the In-substituted SrFe12−xInxO19 hexaferrites was presented based on the neutron diffraction data.
Abstract
While studying the behaviour of a community of blackfin reef sharks, there was a four month long episode during which the entire company of residents and their visitors showed evidence of ...feeling a negative emotion towards me. They directed a variety of menacing gestures towards me, and their behaviour escalated until they began battering my kayak on my arrival in their range. Underwater, three would have slammed me personally had I not fought them off. Their behaviour suggested that their cognitive functions are complex, for they held their negative attitude in mind long-term. Two years later, under different conditions, they conveyed, via body language, a positive emotion. Social learning, social buffering, and emotional contagion were also displayed in their actions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
To some extent, rare-earth-doped UO2 is representative of an irradiated nuclear fuel. The two phases we observed previously in neodymium-doped UO2 are now interpreted as the existence of a ...miscibility gap in the U–Nd–O phase diagram using new results obtained with Raman spectroscopy. Extrapolating the miscibility gap in the U–Nd–O phase diagram to irradiated UO2 opens the path to a new understanding of nuclear oxides in the environment.
Neutron diffraction study of the chiral magnet MnGe Makarova, O. L.; Tsvyashchenko, A. V.; Andre, G. ...
Physical review. B, Condensed matter and materials physics,
05/2012, Letnik:
85, Številka:
20
Journal Article
Recenzirano
The magnetic structure of cubic MnGe has been determined by powder neutron diffraction. MnGe has a helical spin structure with a propagation vector k = (0, 0, zeta), where zeta = 0.107(5) just below ...the transition temperature T sub(N) = 170 K. The zeta value increases upon cooling and locks in to the value of 0.167(4) below 30 K. The moment value is 2.3(5) mu sub(B) at 2 K. The onset of the magnetic order is connected with a symmetry lowering from cubic to orthorhombic.
We have studied the structural properties of industrial Zirconia Toughened Alumina (ZTA) composites for different compositions of zirconia and yttria at the main stages of the process. Influences on ...phases stability, lattice parameters, homogeneous and non-homogeneous strains, particles and crystallites sizes, have been considered and discussed. The structural states are explained from a very delicate balance of three competing effects: yttria-doping, strain and size effect. The first and third one have been shown to stabilize the tetragonal phase relatively to the monoclinic phase, and to destabilize the tetragonal phase relatively to the cubic phase whereas the second one is doing the opposite. In addition to this competition, the most prominent local effects have also being considered to fully understand the microscopic situation: i.e. the micro-strains and the inhomogeneous distribution of yttria which both increases the metastable coexistence of phase. At high yttria content a core–shell structure of the grains is evidenced.
We have performed high-resolution neutron diffraction and inelastic neutron scattering experiments in the frustrated multiferroic hexagonal compounds RMnO_{3} (R = Ho,Yb,Sc,Y), which provide evidence ...of a strong magnetoelastic coupling in the whole family. We can correlate the atomic positions, the type of magnetic structure, and the nature of the spin waves whatever the R ion and temperature. The key parameter is the position of the Mn ions in the unit cell with respect to a critical threshold of 1/3, which determines the sign of the coupling between Mn triangular planes.
The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu
3
Ti
4
O
12
...(CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.
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