Transport, Magnetic, and Thermal Properties of La0.7Ca0.24Sr0.06MnO3 Single Crystal

We report the transport, magnetic, and thermal properties of La0.7Ca0.24Sr0.06MnO3 single crystal. It was prepared using floating zone technique used under oxygen pressure of 1？bar with a typical growth rate of 1？mm/hr. The resistivity data shows the metal to insulator transition (M-I) occuring at ？K along the c-axis and at ？K along the ab-plane. It is observed that the is higher along the c-axis as compared to that in the ab-plane, thus indicating that more favorable hoping of electrons is along the c-axis. From bolometric application point of view, the temperature coefficient of resistance (TCR) is found to be ~28%？K？1. The ac-susceptibility measurement shows that this material exhibits ferromagnetic to paramagnetic transition temperature ( ) 277？K. Sharp peak around this temperature in heat capacity data indicates the onset of long-range ordering. The entropy change associated with this transition is found to be 2.3？J/mol？K. 1. Introduction The colossal magnetoresistance (CMR) of hole doped manganites RE1？xAxMnO3, with RE = La, Nd, and Pr and A = Ba, Sr, Ca, and Pb, is promising magnetoresistance materials in which the change of resistivity by applying magnetic field is so large that this effect is described as colossal. They were studied very intensively in the last few years due to the effect of CMR [1–4]. They exhibit ferromagnetic to paramagnetic (FM-PM) as well as metal to insulator (M-I) transition. The perovskite structure of ABO3 with A = La, Pr, and Nd and B = Mn, is paramagnetic insulator at all temperatures. When these are doped with divalent ion, their resistivity decreases with formation of Mn+4, which decreases the Jahn-Teller distortion, creates double exchange interactions, and hence plays a crucial role in the electrical transport and magnetic properties of these oxides [1]. La1？xAxMnO3 perovskite systems have been studied extensively for their remarkable CMR properties that have technological applications [5]. The CMR behavior occurs near the ferromagnetic (FM) transition temperature, and this remarkable phenomenon is attributed to the magnetic coupling between Mn+3 and Mn+4 ions as well as to the strong electron-phonon coupling arising due to Jahn-Teller splitting of Mn 3d levels. It has also been found that the bond angle and bond length of Mn+3–O？2–Mn+4 play a crucial role in controlling the CMR properties of these manganites as the geometric quantity and the tolerance factor are modified when suitable ions are substituted for La to fill the 3d network of MnO6 octahedra [6]. The problem, however, is that samples used for such