The positron annihilation lifetimes were measured using a 48V positron source in noncentrosymmetric cubic single crystals of CoSi, FeSi and MnSi. The following lifetimes were determined from the ...positron annihilation time spectra: 168(1) ps for CoSi, 114(1) ps for FeSi and 111(1) ps for MnSi. For single-crystal CoSi, the positron annihilation lifetime was also determined with a 22Na positron source. For CoSi, the lifetimes obtained from different positron sources are consistent. The differences in the positron annihilation lifetimes in MnSi and FeSi, on the one hand, and in the Weyl semimetal CoSi, on the other hand, are possibly caused by the formation of a positron + electron bound state (positronium).
We have used the time differential perturbed angular correlation (TDPAC) spectroscopy to measure the electric and magnetic hyperfine fields in RhGe crystallized in the B20 cubic lattice structure and ...weakly doped with Hf (0.5–2 atomic %) in the temperature range from 5 K to 295 K. Two most commonly used nuclei probes, 111In→111Cd and 181Hf→181Ta, have been used. The experimental results combined with theoretical density functional calculations indicate that the In/Cd impurities substitute into the Ge-site whereas the Ta/Hf probes substitute into the Rh-site. It has also been found that the Ta/Hf impurity strongly distorts the local crystal environment, whereas the effect from the In/Cd probe is weak. There are no reliable evidences of the magnetic order in the studied alloys at low temperatures.
•Novel high-pressure phases.•Local studies of both lattice sites in RhGe.•Study of the very weak magnetism in noncentrosymmetric superconductor.•TDPAC measurements on two most commonly used nuclei probes.•TDPAC measurements at low temperatures.•Digital TDPAC spectrometer.
The new metastable high-pressure high-temperature synthesized hexagonal Laves phase compound YbZn2 was investigated. The unit cell parameters, low-temperature Sommerfeld coefficient and Debye ...temperature were determined. X-ray absorption studies and calculations based on dynamical mean-field theory (DMFT) showed the intermediate valence behavior of YbZn2 with mean Yb valence about 2.55. The values of hyperfine electric parameters in Zn (6h) sites were determined by means of 111Cd-time differential perturbed angular correlations and theoretical density functional calculations. DMFT calculations showed that the main contribution to the electron density of states at the Fermi level is due to Yb 4f electrons, while Zn spd electrons lie much lower in energy.
•Novel high-pressure Laves phase.•Yb-based intermediate valent compound.•TDPAC measurements at high pressure.•Primary study of YbZn2 in MgZn2-type structure.•DMFT calculations.
Hyperfine interactions in the Bi
1−
x
La
x
FeO
3
ferrites (where
x
= 0.0225, 0.075, 0.9) have been studied by means of
57
Fe Mössbauer spectroscopy and
140
Ce time differential perturbed angular
γ
–
...γ
correlation methods. The information about the line shift
δ
, the lattice
ε
lat
and the magnetic
ε
mag
contributions to the quadrupole shift
ε
, isotropic
H
is
and anisotropic
H
an
contributions to the hyperfine magnetic field
H
hf
on
57
Fe nuclei, anharmonicity parameter
m
, distribution of the hyperfine magnetic field
p
(
H
hf
), and supertransferred hyperfine magnetic fields on
140
Ce probe nuclei were obtained. In all studied compounds, the Fe ions are in a high-spin trivalent state. In the compounds with
x
= 0.0225 and 0.075 spatially modulated cycloidal magnetic structures exist. It was found that the sign of the effective constant of magnetic anisotropy
K
eff
changes with the variation of
x
from 0.0225 to 0.075. The substitution of Bi by La increases the value of the hyperfine magnetic field on
57
Fe nuclei from 494 kOe in Bi
0.9775
La
0.0225
FeO
3
to 520 kOe in Bi
0.1
La
0.9
FeO
3
, i.e. by 26 kOe, while the corresponding supertransferred hyperfine magnetic field on
140
Ce probe nuclei decreases.
A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under ...the pressure P≤3.1 GPa), neutron powder diffraction and time-differential γ-γ perturbed angular correlations (TDPAC) using 111Cd nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature TCDW=80 K with charge density wave formation and the second transition at TN≈18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them.
•Novel high-pressure phase.•Incommensurate magnetic order in simple cubic structure.•Interplay between charge density wave and magnetism.•TDPAC and neutron powder diffraction measurements at low temperatures.•Resistivity measurements under high pressure.
•Helical magnetic structure based on DMI and effective RKKY interactions.•Small-angle neutron scattering study of MnGe-based helimagnet under high pressure, high field and low temperature.•Evolution ...of field-temperature phase diagram of helical magnets under high pressure.•Stabilisation of quantum fluctuations of the magnetic structure under high pressure.•Nonmagnetic high pressure cell for neutron studies at low temperatures.
The helical magnetic structure of the Mn0.9Fe0.1Ge compound under a quasihydrostatic pressure of up to 1 GPa was investigated by small-angle neutron scattering in a wide range of temperatures (5–300 K) and magnetic fields (0–5 T). It is shown that the wave vector of the magnetic spiral increases with pressure. The field-temperature phase diagrams were plotted for a given compound at pressures up to P = 1 GPa. The temperature dependencies of the values of the magnetic fields corresponding to the beginning of the process of the transition of the polycrystalline sample to the conical phase, Hc1, the end of the process of transition to the conical phase, Hc1m, and the transition to the ferromagnetic phase, Hc2, are shown at different pressures. The applied pressure leads to an increase of all the values of critical magnetic fields at low temperatures, which may indicate the stabilization of the magnetic system under the external pressure. This might be caused by the tendency of the magnetic system to be in a commensurate state. Also, the decrease of the magnetic ordering temperature, Tc, with pressure increase is shown. This indicates the approach of the magnetic system to a quantum phase transition to a disordered state with increase of external pressure.
The measurements of magnetic hyperfine fields (MHF),
H
hf
, and isomer shift, δ, in Y(Fe
1 –
x
Ni
x
)
2
intermetallic compounds (the MgCu
2
structure type) synthesized at high pressure are performed. ...The MHF values that appear on
57
Fe nuclei at a nickel concentration
x
below 20 at % practically do not change and are approximately equal to 22 T, and in the range from
x
= 0.4 to 0.98 they decrease linearly with an increase in the Ni concentration. However, linear extrapolation of the hyperfine field as a function of Ni concentration does not lead to its disappearance in YNi
2
. For YFe
2
, the rotation of the easy axis from the 101 direction to the 111 direction with increasing temperature is found. As the Ni concentration increases to
x
= 0.3 at a temperature of 5 K, the easy magnetization axis 101 is observed, and at
x
= 0.4 the axis changes direction to 100. Based on the shape of the concentration dependence of the hyperfine field, it is assumed that during the crystallization of Y(Fe
1 –
x
Ni
x
)
2
under high pressure conditions, a magnetic moment exists on Ni ions. First-principles calculations of magnetic properties and hyperfine interactions are performed, which are consistent with experiment.
