Electrical and Magnetic Transport Properties of Pr0.1Ca0.9MnO3

Ceramic Pr1−xCaxMnO3 (x = 0.1) samples were prepared by solid-state reaction and the electrical and magnetic transport properties were studied by direct current (DC) and alternating current (AC) methods in different fields. A Curie temperature of 125 K determined by I-V measurements of ceramic Pr1−xCaxMnO3 (x = 0.1) samples is consistent with that from vibrating sample magnetometer (VSM) measurements. Fitting by Arrhenius law, the barrier height of grain boundary is 145 meV which is well coincident with that from fitting the R-T data. The Cole-Cole semicircles and temperature spectrum of impedance in different electrical and magnetic fields show that there is neither notable ER and MR effects above the Curie temperature of Pr0.9Ca0.1MnO3. Introduction Rare-earth doped manganites have attracted extensive efforts for exotic physical features and potential application in spin electronics since colossal magneto resistance (CMR) effect was found in manganese oxides [1-5]. PrMnO3 is an anti-ferromagnetic insulator with a type-A magnetic structure and has a distorted orthorhombic perovskite structure at room temperature. Pr1-xCaxMnO3 shows relatively complicated magnetic and electrical properties for producing hole-type carriers when trivalent Pr3+ is substituted by divalent Ca2+ ion. For example, with increasing x up to x = 0.3, a phase transition from insulator to metal with a colossal electroresistance (CER) effect [6] can be induced by a strong electric field ( > 1000 V) in Pr0.7Ca0.3MnO3 single crystal. On the base of electroresistance effect (ER), electrical pulse induced resistance (EPIR) effect was first reported by S.Q. Liu et. al. in the sandwich structure of Pt/ Pr0.7Ca0.3MnO3/ Pt at room temperature [7]. After the detailed research on EPIR effect by Sawa et al., Pr0.7Ca0.3MnO3 was considered as a potential material for non-volatile resistive random access memory (ReRAM) [8]. In our previous work, we systematically studied the magnetic and electrical properties of Pr0.7Ca0.3MnO3 (x = 0.3) samples, and pointed out that both CER and CMR effect exist in Pr0.3Ca0.3MnO3 for the magnetically related Schottky barrier at grain boundary [9]. In addition, manganites are also good additives for ZnO varistor ceramic. Kutty found that varistors prepared from ZnO with La0.6Sr0.4MnO3 as the forming additive exhibited higher nonlinearity coefficient [10]. Yang found that ZnO ceramic varistors with doping of La0.3Sr0.7MnO3 improved their stability against DC accelerated aging stress [11]. Recently, Kutty found ZnO ceramic varistors doped by CaMnO3 exhibited voltage-limiting current-voltage characteristics with nonlinearity coefficient α up to 380 at low voltages of 1.8-12V/mm[12]. Because Pr1-xCaxMnO3 (x=1) is a ferromagnetic insulator like CaMnO3, there may be some interesting results on electrical properties of ZnO ceramic on the effect of Pr0.9Ca0.1MnO3 addition. In this work, Pr1-xCaxMnO3 (x = 0.1) ceramic samples were fabricated and studied. The result shows that both MR and ER effects are strongly dependent on the Curie temperature, so the two International Conference on Material Science and Application (ICMSA 2015) © 2015. The authors Published by Atlantis Press 408 effects only can be induced below Currier temperature. On the contrary, there is no MR and ER effect above Currier temperature for Pr0.9Ca0.1MnO3. Therefore, very different from Pr0.9Ca0.1MnO3 and Pr0.8Ca0.2MnO3[13], Pr0.9Ca0.1MnO3 is an ferromagnetic insulator at room temperature. Materials and Methods Polycrystalline ceramic sample of Pr1-xCaxMnO3 was fabricated by the conventional solid-state reaction method. Pr6O11, CaCO3 and MnO2 were weighted according to the stoichiometric ratio after the raw material Pr6O11 and CaCO3 were baked at 900 °C and 380 °C for 4 hours, respectively. Then, the powder was mixed sufficiently, grinded, and sintered at 1000°C for decarburization. After that, the powder was grinded again and sintered at high temperature 1350 °C in furnace for 12 hours before cooled down. Afterwards, the burned powder was grinded thirdly, pressed into slice shape, sintered at 1350°C again for 12 hours, and then cooled down to room temperature to obtain Pr1-xCaxMnO3 samples finally. The burning silver method was used to manufacture the electrodes in order to eliminate the contact resistance between the electrodes and the sample’s surface. The magnetic and electronic measurement systems include Keithley 2400 and Wayne Kerr 6420 impedance analyzer for measuring R-T and I-V curves. Results and Discussion There are two ways of two-wire and four-wire method to measure I-V characteristic curves. Resistance measured by the two-wire method usually consists of the resistances from electrode contacts and bulk of sample. However, the resistance measured by the four-wire method can exclude the contact’s resistance and only includes that from the bulk of sample [9]. R-T curves are shown in Fig.1 by both measuring methods to see if there is contacting resistance between silver electrode and the surface of P0.9Ca0.1MnO3. From Fig.1 we can see that the resistances and R-T curves are almost identical in the whole range of temperature, which indicates that the contacting resistance is very small and there is ohmic contact between Ag electrode and Pr0.9Ca0.1MnO3 sample. Fig.1 R – T curves for serial Pr0.9Ca0.1MnO3 samples within a temperature range Fig.2 illustrates I-V characteristics of the Pr0.9Ca0.1MnO3 sample measured by four-wire method in different magnetic fields and temperatures. Since ohmic contact exists betwween Ag electrode and the sample’s surface, the I-V characteristic only reflects electrical properties from the ceramic sample. As shown in Fig.2, we can see that the I-V curves separate for with and without magnetic field when temperature is below 125 K. Furthermore, the discranpancy becomes more remarkable with decreasing temperatures, indicating that there is correlation between resistance and magnetic field at