The effect of artificial boundary grain on the magneto- and electro-transport properties of (1 − x)La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub>+xA (A=Al<sub>2</sub>O<sub>3</sub> and Ag) nanocomposite
Phong Pham, Thanh; Nguyen Luu, Huu; Manh Do, Hung; Thanh Tran, Dang; Khiem Nguyen, Van; Hong Le, Van; Phuc Nguyen, Xuan; Phong Pham, Thanh; Nha Trang Pedagogic College, 1 Nguyen Chanh Street, Nha Trang City, Khanh Hoa Province, Vietnam; Nguyen Luu, Huu; Nha Trang Pedagogic College, 1 Nguyen Chanh Street, Nha Trang City, Khanh Hoa Province, Vietnam; Manh Do, Hung; Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay District, Hanoi, Vietnam; Thanh Tran, Dang; Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay District, Hanoi, Vietnam; Khiem Nguyen, Van; Hong Duc University, 3-307 Le Lai, Thanh Hoa City, Vietnam; Hong Le, Van; Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay District, Hanoi, Vietnam; Phuc Nguyen, Xuan; Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay District, Hanoi, Vietnam
Журнал:
Advances in Natural Sciences: Nanoscience and Nanotechnology
Дата:
2011-06-01
Аннотация:
The magneto- and electro-transport properties of two series of nanocrystalline (1−x)La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub>+xA (A: Al<sub>2</sub>O<sub>3</sub> and Ag) composites have been systematically and thoroughly studied. The observed electronic transport behavior over the whole temperature range (5–300 K), especially the change in metal–insulator transition temperature with increasing Al<sub>2</sub>O<sub>3</sub> and Ag content while the ferromagnetic–paramagnetic transition remained unaffected, was explained by applying a two-component phenomenological model. We have attributed the unusual low-temperature resistivity upturn of composites to a change in charging energy. Most interestingly, magneto-transport measurements showed that the low-field magnetoresistance (LFMR), as well as the high-field magnetoresistance (HFMR), displayed a Curie–Weiss-like law behavior. Basing on the spin-polarized transport of conduction electrons at the grain boundaries, we have analyzed our experimental data and found that the temperature dependence of low- and high-field magnetoresistance is controlled predominantly by the nature of the temperature response of surface magnetization of particles. The competition between grain-boundary pinning strength (k), magnetic field and thermal energy (k<sub>B</sub>T) created the temperature sensitive behavior of magnetoresistance as well as that of surface spin susceptibility (χ <sub>b</sub>).
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