Interplay between transport, magnetic, and ordering phenomena in Sm 1 x Ca x MnO 3 J. Hejtma ´ nek, Z. Jira ´ k, and M. Marys ˇ ko Institute of Physics of ASCR, Cukrovarnicka ´ 10, 16200 Praha 6, Czech Republic C. Martin, A. Maignan, M. Hervieu, and B. Raveau Laboratoire CRISMAT, UMR 6508 Associe au CNRS, ISMRA et Universite ´ de Caen 6, Boulevard du Mare ´chal Juin, 14050 Caen Cedex, France Received 1 July 1999 We present the detailed study of Sm 1-x Ca x MnO 3 with 0.3x 1 probed by electrical resistivity, thermo- electric power, magnetic susceptibility, and thermal conductivity measurements between 10 and 320 K. The transport and thermal data are analyzed supposing polaronic carriers and explanation of experimental results is made in coherence with ordering phenomena recently evidenced by electron diffraction and lattice imaging. Sample Sm 0.7 Ca 0.3 MnO 3 an is insulating ferromagnet without any obvious transport anomalies at T C 95 K. Contrary to that, the compounds with 0.4x 0.75 exhibit, at critical temperature T crit , distinct anomalies in transport and magnetism. Respecting the recent electron microscopy results, these anomalies can be associated to the real space charge ordering of Mn 3+ /Mn 4+ ions, i.e., T crit =T CO . Our experimental data indicate, however, that long-range antiferromagnetic order likely develops at T N 130 K, i.e., well below T CO . The Sm 0.2 Ca 0.8 MnO 3 sample is a C-type antiferromagnet with p-type conductivity at low temperatures. For the samples with x 0.9, the paramagnetic highly conducting state is replaced below T crit =110 K by a ‘‘cluster glass’’ ferromagnetic state. The series is completed by a G-type CaMnO 3 antiferromagnet with T N =122 K. In all studied samples, the heat is conducted mainly by phonons with the mean free path critically limited in dependence of composition and temperature by scattering on impurities Sm/Ca substitution, dynamic and/or static Jahn-Teller modes and spin fluctuations. Nevertheless, for the samples with 0.6x 0.9, which exhibit high electrical resistivity in the paramagnetic state, the thermal conductivity at room temperature comprises significant electronic contribution. S0163-18299901744-0 I. INTRODUCTION The detailed electron diffraction and lattice imaging study of Sm 1 -x Ca x MnO 3 system with 0.4x 0.85, comple- mented by electrical resistivity and magnetization, has been published very recently. 1 Moreover, we have implemented the magnetic and transport study of calcium rich manganites Sm 1 -x Ca x MnO 3 , with 0.85x 1.0. 2 Even a relatively small injection of carries in the parent CaMnO 3 antiferro- magnetic insulator ( T N =122 K) has been shown to lead si- multaneously to metalliclike charge carrier transport in the paramagnetic state and to appearance of ferromagnetic com- ponent below 110 K. The magnetic state in this composi- tional range was described as a cluster glass and is restricted to a compositional range close to x 0.9. Magnetic moment at 10 K increases from 0.05  B /Mn for x =0.975, peaks to 1.15 B /Mn for x =0.88 and abruptly decreases for x 0.86 ( M 0.01 B /Mn). 2 The charge carrier transport in the para- magnetic state in this compositional range was explained supposing polaronic carries with mobility strongly influ- enced by random potential fluctuations due to chemical sub- stitution. Nevertheless the polaron binding energies remain small ( 10 0 meV) thus leading to the metalliclike tempera- ture dependence of the resistivity. Except of x =0.88 sample, exhibiting highest magnetic moment, the chemical disorder together with magnetic frustration lead to thermally activated electrical resistivity below characteristic temperature T CG . Only small resistivity and thermopower anomalies observed at T CG indicated, however, that electrons are not subject to such a fundamental change of behavior as in hole doped colossal magnetoresistance CMR counterparts. For lower calcium concentrations, i.e., 0.4x 0.85, the situation is essentially different. The charge ordering CO phenomena appear and different types of order, in depen- dence of chemical composition, have been proposed: i short-range ( x 0.8), long-range charge ordering either commensurate or incommensurate with a modulation q vec- tor close to x (0.5x 0.75) and ‘‘partially’’ charge ordered state in which single ‘‘Mn 3 + ’’ layers alternate with mixed ‘‘Mn 3 + / Mn 4 + ’’ layers (0.4x 0.5). 1 The onset of the CO ( T CO ) was shown to coincide with an increase of electrical resistivity and decrease of magnetic moment. Studies of Pr 1 -x Ca x MnO 3 and La -1 -x Ca x MnO 3 solid solutions have shown, however, that long-range antiferromagnetic AF or- der, which should naturally follow the CO, is established well below the T CO . 3,4 For the Sm 0.5 Ca 0.5 MnO 3 single crys- tal T N 160 K were claimed. 5 In present paper, we study the charge carrier and heat transport in Sm 1 -x Ca x MnO 3 polycrystalline system with 0.3x 1 and we make attempt to intercorrelate the anoma- lies observed in charge carrier and thermal transport and magnetic susceptibility with ordering phenomena. Further- more, the thermoelectric power and thermal conductivity data are not, unlike to electrical resistivity, fundamentally influenced by a polycrystalline nature of the specimens and enable a better insight into the intrinsic properties of respec- tive material. PHYSICAL REVIEW B 15 NOVEMBER 1999-II VOLUME 60, NUMBER 20 PRB 60 0163-1829/99/6020/140579/$15.00 14 057 ©1999 The American Physical Society