Nanoscale physics

Band structure and magnetic properties of quasi-one-dimensional antiferromagnet (TrMA)MnCl3×2H2O
Kozachenko O.V., Bovgyra O.V., Kovalenko M.V., Kapustianyk V.B.
Solid State Physics Department, Faculty of Physics, Ivan Franko National University of Lviv, 8a, Kyrylo and Mefodiy str., 79005 Lviv, Ukraine. 
E-mail: oleh.bovhyra@lnu.edu.ua

Trimethylammonium trichloromanganate dihydrate crystal, [(CH3)3NH]MnCl3 ·2H2O (TrMAMnCl3·2H2O), belongs to the crystal groups of AMeCl3·2H2O and AMeCl3 (A = N(CH3)4, NH(CH3)3, NH2(CH3)2; Me = Cu, Co, Mn, Ni) have been studied actively, first of all due to their specific magnetic properties at low temperatures. Magnetically these compounds can be considered as the quasi-one-dimensional antiferromagnets where isolated from each other polymeric –MnCl3- chains run along the crystallographic b-axis. There are no references on the first-principles band structure calculation for this crystal; however, such data could be useful for a better understanding of the available experimental data. Geometry optimization and electronic structure calculations are performed using the DFT Quantum-Espresso code. The PBE form of the generalized gradient approximation (GGA) is adopted to describe the exchange correlation interaction. To describe the electronic structures more accurately, we used GGA+U method.  In order to see the effect of Van der Waals interactions, we also perform a calculation with an empirical correction for dispersion interactions added to DFT, called DFT-D2.
The main characteristic feature of the obtained band structure of TrMAMnCl4 crystal is a flatness of the band energy dispersion. The properties of the electronic spectra are described in the context of considering the partial density of electronic states distributions for different magnetic orders of the system: paramagnetic, ferromagnetic and antiferromagnetic. The top valence band states are almost entirely the electron states of MnCl4 groups. The energy states of the conduction band would be considered as the common ones for MnCl4, TrMA and H2O groups of the crystal. The obtained results show the dependence of the magnetic exchange interaction on the Hubbard U parameter and that the compound has a stable one-dimensional antiferromagnetic structure.

Acknowledgment. The work was performed within the project 2020.02/0130 “Multifunctional organic-inorganic magnetoelectric, photovoltaic and scintillation materials” (reg. № 0120U104913) due to grant support of the National Research Foundation of Ukraine.