SIPS2019 by FLOGEN Star Outreach

DETAILLED PROGRAM OVERVIEW

Future of Electron Correlated Materials: from Multiferroics to Nanomagnets and to Thermoelectrics
Bernard Raveau¹;
¹UNIVERSITY OF CAEN, Normandy, France;
PAPER: 171/Chemistry/Plenary (Oral)
SCHEDULED: 15:55/Sat. 26 Oct. 2019/Aphrodite A (100/Gr. F)

ABSTRACT:
Numerous studies have been performed these last three decades on perovskites and derivatives showing the possibility to create and to tailor exciting physical properties. This has been previously exemplified by the high Tc superconducting cuprates, the colossal magnetoresistance manganates and the thermoelectric cobaltates. Herein we describe several new classes of materials that appear most promising for the generation of attractive physical/ chemical properties and applications. Multiferroic materials, involving the coexistence of ferroelectricity and ferromagnetism, have been the object of numerous investigations due to their potential application for memory devices. In this respect, oxides with a triangular sub-lattice present a rich potential which to date has not been fully investigated. The mixed valent "114" tetrahedral cobaltates open the route to attractive multiferroic properties as exemplified by the magneto-electric ferrimagnet CaBaCo4O7 which exhibits gigantic magnetic field induced polarization and high magneto-electric coupling. Beside oxides, Hybrid organic-inorganic frameworks (HOIF) represent an important source for the realization of multiferroic properties which has been, to date, insufficiently explored. In particular, transition metal phosphonates with a layered structure offer a potential for the realization of magneto-electric properties by coupling spins of the inorganic layers with electric dipoles of the organic layers. This is illustrated by the non-centro symmetric layered metal-phosphonate, MnO3PC6H4Br.H2O, whose structure consists of perovskite layers stacked with organic bromo-phenyl layers. This compound has been designed from the layered phosphonate MnO3PC6H5.H2O; It exhibits complex magnetic features which are exactly captured in T and H-dependent dielectric constants, ɛ'(T) and ɛ'(H). This demonstrates direct ME coupling in this designed hybrid and yields a new path to design a magnetoelectric hybrid. Low dimensional magnets, especially single molecule magnets (SMM) and single chain magnets (SCM) have been thoroughly investigated in metal organic frameworks in view of applications in quantum computing, spintronics and memory devices. In contrast, similar features were only recently reported for spin chain oxides built up of face-sharing MnO6 octahedra and CoO6 trigonal prisms. We describe the huge potential of one dimensional A1x+(Mn2-xCox)O3+δ oxides with A=Ca, Sr, Ba whose aperiodic structures can be designed by considering a mechanism of extra oxygen incorporation (EOI). We show that these oxides exhibit a crossover from a single chain magnet (SCM) to a long range order (LRO), or more exactly, to a partially disordered antiferromagnetic (PDA) behavior. Thermoelectric (TE) materials, which allow the conversion of waste heat into clean electricity, have been the object of extensive investigations in last fifteen years. Quite a limited number of sulfides have been investigated to date in spite of the rich crystal chemistry of these materials that offers a promising route for the discovery of new physical properties. This is exemplified by the copper rich sulfides with a 3D tetrahedral conductive "Cu-S" framework. The presence of large amounts of univalent copper in these materials makes them remarkable p-type thermoelectrics. Various frameworks can be realized by mimicking the natural minerals such as stannite, bornite, colusite, germanite and stannoidite. The very recent discovery of the thermoelectric colusites Cu26T2Ge6S32 with T=Mo, W, Cr which exhibit outstanding power factors and high ZT figures of merit, illustrates the great potential of these materials.