No abstract

No abstract

No abstract

No abstract

The electrical transport and magnetoresistance properties of the polycrystalline La 0.67 Ca 0.33 MnO 3 film produced on a Pyrex substrate were investigated for the first time. X-ray powder diffraction indicated that the film sample has a perovskite structure. Scanning electron microscope indicated that La 0.67 Ca 0.33 MnO 3 film thickness is approximately 500 nm, and the average grain size of this sample varies between 40 and 50 nm. La 0.67 Ca 0.33 MnO 3 film showed a phase transition from paramagnetic to ferromagnetic at (T C ) 80 K and a metal-insulator transition at (T MI ) 77.5 K and at 2 mT magnetic field. The upturn of the resistance observed at low temperatures (<36 K) was attributed to the Coulomb blockade, and the strong structural disorder is due to the large lattice mismatch and strain relaxation. A large magnetoresistance ratio [MR (%)] of 780% was observed at 100 K and 6 T magnetic field.

A system for the simultaneous measurement of thermoelectric power and resistivity of one and/or two samples over a temperature range of 300–1000 K in a vacuum chamber is designed and implemented. A sample probe is developed to provide its easy mounting and usage. In addition, two samples can be measured at the same time. Measurement accuracy has been enhanced by beadless thermocouples and micro-heaters that are specifically designed in order to minimize the ‘cold-finger effect’ and to eliminate some possible source of contact, design and measurement errors. A broad range of physical types and shapes of samples, such as bulk, bar or disc, can be measured by a software controlled system. A differential steady-state method has been applied for Seebeck coefficient measurement. Resistivity measurement is conducted with the axial technique of the four-point probe method. Platinum wire and a niobium rod are chosen as the standard samples. The total data error for the Seebeck coefficient and resistivity measurements is estimated to be less than 2.6% and 1%, respectively.

No abstract

No abstract