Magnetotransport evidence of irreversible spin reorientation in the collinear antiferromagnetic state of underdoped Nd2−xCexCuO4\mathrm{Nd}_{2-x}\mathrm{Ce}_x\mathrm{CuO}_4

We make use of the strong spin-charge coupling in the electron-doped cuprate $\mathrm{Nd}_{2-x}\mathrm{Ce}_x\mathrm{CuO}_4$ to probe changes in its spin system via magnetotransport measurements. We present a detailed study of the out-of-plane magnetoresistance in underdoped single crystals of this compound, including the nonsuperconducting, $0.05\,\leq x\,\leq 0.115$, and superconducting, $0.12\,\leq x\,\leq 0.13$, compositions. Special focus is put on the dependence of the magnetoresistance on the field orientation in the plane of the CuO$_2$ layers. In addition to the kink at the field-induced transition between the noncollinear and collinear antiferromagnetic configurations, a sharp irreversible feature is found in the angle-dependent magnetoresistance of all samples in the high-field regime, at field orientations around the Cu--O--Cu direction. The obtained behavior can be explained in terms of field-induced reorientation of Cu$^{2+}$ spins within the collinear antiferromagnetic state. It is, therefore, considered as an unambiguous indication of the long-range magnetic order

Unconventional charge density wave in the organic conductor alpha-(BEDT-TTF)_2KHg(SCN)_4

The low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 salt is known for its surprising angular dependent magnetoresistance (ADMR), which has been studied intensively in the last decade. However, the nature of the LTP has not been understood until now. Here we analyse theoretically ADMR in unconventional (or nodal) charge density wave (UCDW). In magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to spectacular ADMR. The present model accounts for many striking features of ADMR data in alpha-(BEDT-TTF)_2KHg(SCN)_4.Comment: 5 pages, 6 figure

Fermi surface properties of the bifunctional organic metal κ-(BETS)2Mn[N(CN)2]3 near the metal-insulator transition

We present detailed studies of the high-field magnetoresistance of the layered organic metal κ-(BETS)2Mn- [N(CN)2]3 under a pressure slightly above the insulator-metal transition. The experimental data are analyzed in terms of the Fermi surface properties and compared with the results of first-principles band structure calculations. The calculated size and shape of the in-plane Fermi surface are in very good agreement with those derived from Shubnikov-de Haas oscillations as well as the classical angle-dependent magnetoresistance oscillations. A comparison of the experimentally obtained effective cyclotron masses with the calculated band masses reveals electron correlations significantly dependent on the electron momentum. The momentum- or band-dependent mobility is also reflected in the behavior of the classical magnetoresistance anisotropy in a magnetic field parallel to layers. Other characteristics of the conducting system related to interlayer charge transfer and scattering mechanisms are discussed based on the experimental data. Besides the known high-field effects associated with the Fermi surface geometry, new pronounced features have been found in the angle-dependent magnetoresistance, which might be caused by coupling of the metallic charge transport to a magnetic instability in proximity to the metal-insulator phase boundary.We are grateful to N.D. Kushch for providing the high-quality crystals for our studies and to P.D. Grigoriev for numerous useful discussions. The work was supported by the German Research Foundation (DFG) via the Grant No. KA 1652/4-1. The high-field measurements were done under support of the LNCMI-CNRS, member of the European Magnetic Field Laboratory (EMFL). V.N.Z. acknowledges the support from RFBR Grant No. 18-02-00280. Work in Spain was supported by the Spanish Ministerio de Economa y Competitividad (Grants No. FIS2015-64886-C5-4-P and No. CTQ2015-64579-C3-3-P) and Generalitat de Catalunya (2017SGR1506, 2017SGR1289, and XRQTC). E.C. acknowledges support from the Severo Ochoa Centers of Excellence Program under Grant No. SEV-2015-0496. P.A. acknowledges support from the Maria de Maeztu Units of Excellence Program under Grant No. MDM-2017-0767.Peer reviewe

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