97 research outputs found
Magnetic-field tuning of the spin dynamics in the magnetic topological insulators (MnBi<sub>2</sub>Te<sub>4</sub>)(Bi<sub>2</sub>Te<sub>3)</sub><i>n</i>
We report a high-frequency/high-magnetic field electron spin resonance (HF-ESR) spectroscopy study in the sub-THz frequency domain of the two representatives of the family of magnetic topological insulators (MnBi2Te4)(Bi2Te3)n with n = 0 and 1. The HF-ESR measurements in the magnetically ordered state at a low temperature of T=4K combined with the calculations of the resonance modes showed that the spin dynamics in MnBi4Te7 is typical for an anisotropic easy-axis type ferromagnet whereas MnBi2Te4 demonstrates excitations of an anisotropic easy-axis type antiferromagnet. However, by applying the field stronger than a threshold value ∼6T, we observed in MnBi2Te4 a crossover from the antiferromagnetic (AFM) resonance modes to the ferromagnetic (FM) modes, whose properties are very similar to the FM response of MnBi4Te7. We attribute this remarkably unusual effect unexpected for a canonical easy-axis antiferromagnet, which, additionally, can be accurately reproduced by numerical calculations of the excitation modes, to the closeness of the strength of the AFM exchange and magnetic anisotropy energies which appears to be a very specific feature of this compound. Our experimental data evidences that the spin dynamics of the magnetic building blocks of these compounds, the Mn-based septuple layers (SLs), is inherently ferromagnetic, featuring persisting short-range FM correlations far above the magnetic ordering temperature as soon as the SLs get decoupled either by introducing a nonmagnetic quintuple interlayer, as in MnBi4Te7, or by applying a moderate magnetic field, as in MnBi2Te4, which may have an effect on the surface topological band structure of these compounds.</p
The kabachnik-fields and pudovik reactions on the basis of E,Z-citral and its imines and (R,S)-citronellal
The Kabachnik-Fields reaction of E,Z-citral with diethyl phosphite in the presence of isobutylamine has been found to form α-aminophosphonates. The Pudovik reactions of diethyl phosphite with prenyl imines prepared on the basis of E,Z-citral with isobutylamine also allowed us to obtain the same α-aminophosphonates. We have managed to synthesize α- aminophosphonates by the reaction of O,O-dialkyl trimethylsilyl phosphites with prenyl imines in the presence of water or diethylamine. α- Aminophosphonates were also synthesized by the reaction of diethyl phosphite with (R,S)-citronellal in the presence of alkylamines. α-Aminophosphonates obtained showed bacteriostatic activity against Staphylococcus aureus and Bacillus cereus. © 2012 Wiley Periodicals, Inc
Evolution of the spin dynamics in the van der Waals system PS ( = Mn, MnNi, Ni) series probed by electron spin resonance spectroscopy
In this work we report a detailed ESR spectroscopic study of the
single-crystalline samples of the van der Waals compounds
PS ( = Mn,
MnNi, Ni), performed at an excitation frequency of 9.56 GHz, in a
broad range of temperatures above the magnetic order, and at different
orientations of the magnetic field with respect to the sample. Analyzing
temperature and angular dependences of the resonance field and of the linewidth
of the MnPS compound we have observed a significant change of the
spin dynamics from the dominance of the 3D-like fluctuations close to the
magnetic order to a relative increase of the 2D-like spin fluctuations at
higher temperatures. Such a behavior, which is opposite to the development of
the low-D signatures in the previously studied
CrGeTe compound, can be explained by the
difference in the type of magnetic order in MnPS and
CrGeTe. On the other hand,
MnNiPS compound exhibits angular dependences of the linewidth typical
for the system with 3D-like spin correlations in the whole measurement
temperature range, however the 2D-like correlations can be seen in the
temperature dependences of the resonance field and the linewidth.
NiPS, in turn, does not show any 2D signatures. This suggests that
varying the Ni content in (MnNi)PS one can control the
exchange interaction, possibly also in the third dimension
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