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Ivan Baev

Publications and source records attributed to Ivan Baev.

5 recordsLinked to original sources
arXiv2023

Evidence for Conical Magnetic Structure in M-type BaFe12O19 Hexaferrite: A Combined Single-Crystal XMCD and Neutron Diffraction Study

The magnetic ground state of BaFe12O19 (BFO) was investigated using X-ray absorption at 1.2 K and 1.5 K, respectively. The XMCD measurements on single-crystals of BFO in grazing incidence geometry reveal the canting of the spins away from the c-axis of the hexagonal unit cell. Single-crystal neutron diffraction studies reveal magnetic satellite peaks along the 00l reciprocal lattice row around the forbidden l = 2n +/- 1 positions confirming conical-type magnetic structure in the ground state of BFO. The observation of the conical magnetic structure of BFO opens the possibility of type-II multiferroicity in undoped BFO also.

cond-mat.mtrl-sci↗
arXiv2020

Electronic Quantum Coherence in Glycine Molecules Probed with Ultrashort X-ray Pulses in Real Time

Quantum coherence between electronic states of a photoionized molecule and the resulting process of ultrafast electron-hole migration have been put forward as a possible quantum mechanism of charge-directed reactivity governing the photoionization-induced molecular decomposition. Attosecond experiments based on the indirect (fragment ion-based) characterization of the proposed electronic phenomena suggest that the photoionization-induced electronic coherence can survive for tens of femtoseconds, while some theoretical studies predict much faster decay of the coherence due to the quantum uncertainty in the nuclear positions and the nuclear-motion effects. The open questions are: do long-lived electronic quantum coherences exist in complex molecules and can they be probed directly, i.e. via electronic observables? Here, we use x-rays both to create and to directly probe quantum coherence in the photoionized amino acid glycine. The outgoing photoelectron wave leaves behind a positively charged ion that is in a coherent superposition of quantum mechanical eigenstates lying within the ionizing pulse spectral bandwidth. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay and by the photoelectron emission from sequential double photoionization. Sinusoidal temporal modulation of the detected signal at early times (0 - 25 fs) is observed in both measurements. Advanced ab initio many-electron simulations, taking into account the quantum uncertainty in the nuclear positions, allow us to explain the first 25 fs of the detected coherent quantum evolution in terms of the electronic coherence.

physics.chem-ph↗
arXiv2019

Magnetic ordering in metal-free radical thin films

Molecular systems are materials that intersect with many different promising fields such as organic/molecular electronics and spintronics, organic magnetism and quantum computing1-7. Particularly, magnetism in organic materials is very intriguing: the possibility to realize long-range magnetic order in completely metal-free systems means that magnetic moments are coupled to useful properties of organic materials, such as optical transparency, low-cost fabrication, and flexible chemical design. Magnetic ordering in light elements, such as nitrogen and carbon, has been studied in magnetic-edged graphene nanoribbons8 and bilayers9, and polymers10 while in organic thin films most of the investigations show this effect as due to the proximity of light atoms to heavy metals, impurities, or vacancies11. Purely organic radicals are molecules that carry one unpaired electron giving rise to a permanent magnetic moment, in the complete absence of metal ions.12-14 Inspired by their tremendous potential, here we investigate thin films of an exceptionally chemically stable Blatter radical derivative15 by using X-ray magnetic circular dichroism (XMCD)16-18. Here we observe XMCD at the nitrogen K-edge. Our results show a magnetic ordering different than in the single crystals and calculations indicate, although weak, a long-range intermolecular coupling. We anticipate our work to be a starting point for investigating and modelling magnetic behaviour in purely organic thin films. The tuning of the magnetic properties by the molecular arrangement in organic films is an exciting perspective towards revealing new properties and applications.

cond-mat.mtrl-sci↗
arXiv2016

Ultrafast charge redistribution in small iodine containing molecules

The competition between intra molecular charge redistribution and fragmentation has been studied in small molecules containing iodine by using intense ultrashort pulses in the extreme ultraviolet regime (XUV). We show that after an element specific inner-shell photoionization of diiodomethane (CH$_2$I$_2$) and iodomethane (CH$_3$I), the induced positive charge is redistributed with a significantly different efficiency. Therefore, we analyze ion time-of-flight data obtained from XUV-pump XUV-probe experiments at the Free Electron Laser in Hamburg (FLASH). Theoretical considerations on the basis of ab initio electronic structure calculations including correlations relate this effect to a strongly molecule specific, purely electronic charge redistribution process that takes place directly after photoionization causing a distribution of the induced positive charge predominantly on the atoms which exhibit the lowest atomic ionization potential, i.e, in the molecules considered, the iodine atom(s). As a result of the very different initial charge distributions, the fragmentation timescales of the two molecules experimentally observed are strikingly different.

physics.chem-ph↗