Bose-Einstein Condensation in Magnetic Insulators

The elementary excitations in antiferromagnets are magnons, quasiparticles with integer spin and Bose statistics. In an experiment their density is controlled efficiently by an applied magnetic field and can be made finite to cause the formation of a Bose-Einstein condensate (BEC). Studies of magnon condensation in a growing number of magnetic materials provide a unique window into an exciting world of quantum phase transitions (QPT) and exotic quantum states.Comment: 17 pages, 3 figure

Properties of Mn2+ and Π-Electron Spin Systems Probed by 1H and 13C NMR in the Organic Conductor κ-(BETS)2Mn[N(CN)2]3

Properties of the spin systems of the localized 3d Mn2+ ions and the conduction π electrons in quasi-two-dimensional organic conductor κ-(BETS)2Mn[N(CN)2]3 were accessed using 1H and 13C NMR in order to find their relation to the metal-insulator transition which occurs at ∼23 K. The transition of the system into the insulating state is shown to be followed by localization of the π spins into a long-range ordered staggered structure of AF type. In contrast, the 3d Mn2+ electron spin moments form a disordered tilted structure, which may signify their trend to AF order, frustrated geometrically by the triangular arrangement of Mn in the anion layer. This result suggests that the MI transition in κ-(BETS)2Mn[N(CN)2]3 is not the consequence of the interactions within the Mn2+ spins but due to the interactions within the π-electron system itself. Vice versa, it is more likelythat the disordered tilted structure of the Mn2+ spins is induced by the ordered π-spins via the π-d interaction

New radical cation salt κ-(BETS)2Co0.13Mn0.87[N(CN)2]3 with two magnetic metals: Synthesis, structure, conductivity and magnetic peculiarities

A new metallic radical cation salt κ-(BETS)2Co0.13Mn0.87[N(CN)2]3, where BETS is bis(ethylenedithio)tetraselenafulvalene, C10S4Se4H8, has been synthesized. In this salt, a part of Mn2+ ions are replaced by Co2+ which acts as a magnetic dopant with a different effective magnetic moment. Crystal structure, band structure, conducting and magnetic properties of the salt have been studied. Below 30 K the material undergoes a metal-insulator transition, which is suppressed by applying a pressure of ~ 0.5 kbar, leading to a superconducting ground state. While the structural and conducting properties are very similar to those of the parent salt κ-(BETS)2Mn[N(CN)2]3, magnetic properties associated with localized moments in the anion layer are found to be surprisingly different.We thank Prof. A. Kobayashi for providing BETS used in the work. N.D.K. and E.B.Y. were supported by the RFBR grant No. 14-0300119 and by Program No. 2 of the Presidium of the Russian Academy of Sciences. N.D.K., O.M.V, W.B., and M.V.K. acknowledge support by the German Research Foundation (DFG) via the grant KA 1652/4-1. E.C. acknowledges support by MINECO (Spain) through Grant FIS2015-64886-C5-4-P, Generalitat de Catalunya (2014SGR301), and by the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2015-0496.Peer reviewe