The Structure And Physical Properties Of Ca,Ga Doped ErMnO₃

As a strong correlated electron system,rare earth manganites?RMnO₃?have attracted much attention because they exhibit abundant physical properties such as charge ordering,multiferric,colossal magnetoresistance?CMR?,etc.Up to date,most investigation focuses on light rare earth manganites,while little attention has been paid to manganites with small A site ion size,whose data are necessary to deep understand the physical properties of RMnO₃ system.Therefore,ErMnO₃ is selected as parent material,and the evolution of its structure,magnetism,transport properties,and dielectric properties is studied by A-and B-site doping with Ca and Ga,respectively.Hexagonal ErMn_1-xGa_xO₃ samples were prepared by solid state reaction at 1350 °C,with intermediate grinding.Lattice parameter a is found to decrease,while c increase with increasing Ga doping,as indicated by refinement data.Ga doping enhances lattice distortion.ErMn_1-xGa_xO₃ exhibits ferroelectricity at room temperature,with a dielectric susceptibility of 103 magnitude.The dielectric susceptibility at low frequencies increases significantly,indicating that Ga doping enhances its low frequency performance.After processing of hexagonal ErMn_1-xGa_xO₃ materials under high pressure?4 GPa?combined with high temperature?1000 ° C?,orthorhombic samples were obtained.Jahn-Teller distortion is decreased with Ga doping,resulting in the increase of b,while the decrease of a,c,and the volume of primitive cell as well.Ga doping introduces vibronic interaction,dilute the Mn3+ions at B-site,enhances ferromagnetic interaction in the materials,hence both paramagnetic Curie temperature and TN decrease.Vibronic interaction enhances the mobility of electrons,giving a low resistance and large dielectric susceptibility.However,the energy dissipation caused by vibronic interaction enhances the dielectric loss in the materials.Both solid state reaction and high pressure – high temperature route are adopted to synthesize orthorhombic Er_1-xGa_xMnO₃?x=0-0.5?,wherein the x=0.3-0.5 samples were prepared by the former,and the x=0.1-0.2 samples by the latter.With higher Ca content,the lattice distortion of Er_1-xGa_xMnO₃ decreases,giving shorter a,and longer b and c.No ferromagnetism is found in Er_1-xGa_xMnO₃,and magnetic glass state emerges by the competition between ferromagnetic and antiferromagnetic interaction?The severe lattice distortion in Er_1-xGa_xMnO₃ results in the slow decrease of TN with increasing Cacontent.Semiconductor-like transport properties were observed in Ca doped samples,i.e.,thermal activation mechanism at low Ca content,while variable range hopping mechanism at high doping level.