Crystal structure, magnetic properties and conductivity mechanisms of La0.7Ca0.3Mn0.5Fe0.5O3

La0.7Ca0.3Mn0.5Fe0.5O3 (LCMFO) ceramic samples were prepared by conventional solid-state reaction. X-Ray diffraction investigations show that samples have orthorhombic space group Pnma (a = 5.447(2) Ǻ, b = 7.709(3) Ǻ, c = 5.467(3) Ǻ). During the neutron powder diffraction measurements of LCMFO in the temperature range of 10 ÷ 300 K the antiferromagnetic long-range ordering of G-type was seen. It has been established that 50% substitution of Mn/Fe leads to a complete suppression of the ferromagnetism in LCMFO samples. Investigations of temperature dependence of the magnetization, M(T), suggests the frustration of magnetic ground state and the existence of a spin-glass or a cluster-glass phase below the magnetic transition temperature close to 350 K. The temperature dependences of conductivity for La0.7Ca0.3Mn0.5Fe0.5O3 sample investigated in magnetic fields B = 0 and 1 T. According to the research, the mechanisms of hopping conductivity were established. Micro parameters in density of localized states were calculated for LCMFO samples. The width of the Coulomb gap Δ = 0.67 eV, rigid gap δ = 0.324 eV and the localization radii of charge carriers were estimated. © 2016 Taylor & Francis Group, LLC

Crystal structure, magnetic properties and conductivity mechanisms of La0.7Ca0.3Mn0.5Fe0.5O3

La0.7Ca0.3Mn0.5Fe0.5O3 (LCMFO) ceramic samples were prepared by conventional solid-state reaction. X-Ray diffraction investigations show that samples have orthorhombic space group Pnma (a = 5.447(2) Ǻ, b = 7.709(3) Ǻ, c = 5.467(3) Ǻ). During the neutron powder diffraction measurements of LCMFO in the temperature range of 10 ÷ 300 K the antiferromagnetic long-range ordering of G-type was seen. It has been established that 50% substitution of Mn/Fe leads to a complete suppression of the ferromagnetism in LCMFO samples. Investigations of temperature dependence of the magnetization, M(T), suggests the frustration of magnetic ground state and the existence of a spin-glass or a cluster-glass phase below the magnetic transition temperature close to 350 K. The temperature dependences of conductivity for La0.7Ca0.3Mn0.5Fe0.5O3 sample investigated in magnetic fields B = 0 and 1 T. According to the research, the mechanisms of hopping conductivity were established. Micro parameters in density of localized states were calculated for LCMFO samples. The width of the Coulomb gap Δ = 0.67 eV, rigid gap δ = 0.324 eV and the localization radii of charge carriers were estimated. © 2016 Taylor & Francis Group, LLC

Crystal structure and vibrational spectra of hexagonal manganites YMnO3 and LuMnO3 under high pressure

The structural and vibrational properties of the multiferroics YMnO3 and LuMnO3 have been studied by means of the x-ray diffraction and Raman spectroscopy at high pressures up to 29.3 and 31.2 GPa, respectively. The initial hexagonal structure with space group P6(3)cm of both compounds remains unchanged in the entire pressure range. The anisotropic baric behaviors of lattice parameters and vibration modes of studied compounds were observed. The structural mechanisms of those phenomena are discussed. ©2019 IOP Publishing Ltd11sciescopu

Studies on alpha-induced astrophysical reactions using the low-energy RI beam separator CRIB

Several alpha-induced astrophysical reactions have been studied at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. Two major methods to study them are the α resonant scattering, and direct measurements of (α,p) reactions using an active or inactive helium gas target. Among the recent studies at CRIB, the measurement of 7Be+α resonant scattering is discussed

Studies on alpha-induced astrophysical reactions using the low-energy RI beam separator CRIB

Several alpha-induced astrophysical reactions have been studied at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. Two major methods to study them are the α resonant scattering, and direct measurements of (α,p) reactions using an active or inactive helium gas target. Among the recent studies at CRIB, the measurement of 7Be+α resonant scattering is discussed

Dipole excitations of neutron-proton asymmetric nuclei

Dipole excitations of unstable short-lived nuclei has been investigated experimentally by utilizing the electromagnetic-excitation process with high-energy secondary beams. From an exclusive measurement of the neutron-decay channels, differential cross sections with respect to excitation energy, which are directly related to the photo-absorption cross section and accordingly to the dipole-strength function, have been derived. Light neutron-rich nuclei in the mass range fromA = 11 toA = 23 with mass-over-charge ratios up toA/Z≈ 2.8 have been investigated systematically. Much in contrast to stable nuclei, low-lying dipole excitations well below the giant dipole resonance region have been observed as a general phenomenon for these neutron-proton asymmetric nuclei. For the neutron-rich oxygen isotopes, for instance, low-lyingE1 strength has been observed exhausting about 10% of the classical dipole sum rule below 15 MeV excitation energy. A quantitative analysis of low-lying threshold strength for loosely bound nuclei indicates that the characteristics of the dipole strength is directly related to the ground-state single-particle structure of the valence nucleon in the projectile

Experimental investigation of a linear-chain structure in the nucleus 14C

It is a well-known fact that a cluster of nucleons can be formed in the interior of an atomic nucleus, and such clusters may occupy molecular-like orbitals, showing characteristics similar to normal molecules consisting of atoms. Chemical molecules having a linear alignment are commonly seen in nature, such as carbon dioxide. A similar linear alignment of the nuclear clusters, referred to as linear-chain cluster state (LCCS), has been studied since the 1950s, however, up to now there is no clear experimental evidence demonstrating the existence of such a state. Recently, it was proposed that an excess of neutrons may offer just such a stabilizing mechanism, revitalizing interest in the nuclear LCCS, specifically with predictions for their emergence in neutron-rich carbon isotopes. Here we present the experimental observation of α-cluster states in the radioactive 14C nucleus. Using the Be10+α resonant scattering method with a radioactive beam, we observed a series of levels which completely agree with theoretically predicted levels having an explicit linear-chain cluster configuration. We regard this as the first strong indication of the linear-chain clustered nucleus

Structure of 80Ge revealed by the β decay of isomeric states in 80Ga: Triaxiality in the vicinity of 78Ni

The decays of two long-lived low-lying isomeric states of 80Ga were studied at the PARRNe mass separator of the ALTO ISOL facility. Over the 75 γ rays previously attributed to the 80Ga decay, the decay time of 67 individual β-delayed γ activities were measured. This allowed the determination of the decay time of these two recently reported long-lived--actually β-decaying--states as well as to partially disentangle the two decay schemes. Thanks to the relatively high spin difference between these two 80Ga isomers spin assignments of the daughter 80Ge states could be further constrained rendering the comparison with calculations easier. From this comparison it appears that the suspected maximum of collectivity at Z = 32 along the N = 50 line should express itself through the coexistence of spherical and collective γ -soft structures