Structure, magnetic and electrical properties of Ln2/3Pb1/3MnO3 (Ln = La, Pr, Nd) films
Ln2/3Pb1/3MnO3 (Ln = La, Pr, Nd) films deposited on single crystal LaAlO3 substrate were fabricated using the RF magnetron sputtering method. The X-ray diffraction results of bulk targets indicate that with the decrease of the average ion radius < rA >, the structure transits from the rhombohedral to the orthorhombic phase. The magnetic properties show that there is a transition from the ferromagnetic to the paramagnetic state with the increase in temperature, the Curie temperature reduces abruptly with the decrease of < rA >. The electrical properties show that films are in the metallic state, which can be fitted to the formula: ρ(T) = ρ0 + ρ1T2 + ρ2T4.5 at low temperatures and the insulator state, which can be fitted to the formula: ρ(T) = ρ0T exp(Ea/KBT) at higher temperature(T > TMI). The temperature range of the ferromagnetic metallic state becomes narrow with the decrease of < rA >. The phenomenon can be qualitatively and reasonably explained by the double-exchange model and Jahn–Teller effects. PACS Nos.: 75.47.Lx, 74.25.Ha, 75.47.–m, 75.30.Et