Neutron diffraction investigation of structural and magnetic states of lithium-doped antiferromagnet NiO

The elastic neutron scattering in polycrystalline samples of the (Ni_1−x Li_x)O solid solutions (x<0.1) is investigated by neutron diffraction technique. It is shown for the first time that the doping of nickel monoxide by lithium is accompanied by the formation of vacancies in the anionic sublattice, and the vacancy concentration is equal to the lithium content in the solid solution. The neutral lithium atoms are randomly arranged over sites of the cationic sublattice with possible spatial polarization of a valence electron toward an oxygen vacancy. In the composition range studied, the diamagnetic dilution of nickel monoxide by lithium turns out to be magnetically similar to the dilution with magnesium. In both cases, the Néel temperature and the mean magnetic moment per atom linearly decrease with an increase in concentration of the diamagnetic dopant.     

Magnetic phases in quasi-binary (Fe1−x Cox)Ge2 intermetallic compounds

Magnetic neutron diffractometry revealed the existence in (Fe_1−x Co_x)Ge₂ solid solutions (x<0.5) with C16 structure of only two magnetic phases, namely, low-temperature (AFI) and high-temperature (AFII). A third magnetic phase, AFIII, suggested by earlier magnetic measurements, has not been found. The AFI and AFII phases have a commensurate and an incommensurate antiferromagnetic structure with the wave vectors k ₀=2π/a (1,0,0) and k=k ₀+δ k, respectively. The regions of their existence are shown in the magnetic phase diagram. Neutron diffraction measurements yielded the concentration dependence of the average magnetic moment per atom in the antiferromagnetic sublattice of a 3d metal, which, similarly to the dependence of the Néel point on x, was found to be nonlinear. An analysis of these dependences suggests that substitution of cobalt for iron is accompanied, on the one hand, by a decrease of the local spin density on the iron atoms in the nearest environment of a cobalt atom and, on the other hand, by an increase of the effective exchange integral between the nearest-neighbor iron atoms located along the tetragonal axis. Fiz. Tverd. Tela (St. Petersburg) 41, 283–289 (February 1999)     

Nulling Phenomenon of the New Radio Pulsar J0810+37 at a Frequency of 111 MHz

Pulsar J0810+37 with a period of 1.2483 s is detected at a frequency of 111 MHz during the pulsar search at the Big Scanning Antenna (BSA) radio telescope of the Lebedev Physical Institute [1]. In this paper, we present the results of the detailed study of radio emission from J0810+37 which exhibits a rare nulling effect of different durations in a very wide time interval with an average nulling fraction in “switch-on” days 〈NF〉 = 38%; considering “switch-off” days, 〈NF〉 = 74%, since radio emission from this source is interrupted on average by 2–3 days, and then it again revives on average for 1–2 days. The “switch-off” periods reach 7 days.     

Magnetic structure of the Nd5Ge3 compound

Neutron diffraction measurements of the Nd₅Ge₃ intermetallic compound with a hexagonal structure (space group P6₃/mcm) have been performed at temperatures of ～10 and 293 K. The basis functions of irreducible representations of the space group D _6h ³ (P6₃/mcm), which are calculated as a result of the symmetry analysis of possible magnetic structures with the wave vector k = μb ₁, are used to facilitate the search for a real model of the magnetic structure of the compound.