Advances in Natural Sciences, T. 7, S. 1 (2006)

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Influence of Substitution of the Magnetic 3d Metals for Mn in Perovskite La0.67Ca0.33Mn0.90TM0.10O3 (TM = Fe, Co, Ni) Compounds

Nguyen Huy Sinh, Vu Thanh Mai, Pham Hong Quang

Tóm tắt

Influence of substitution of 3d metals for Mn on properties of La0.67Ca0.33Mn0.9
TM0.1O3 (TM = Fe, Co, Ni) compounds was studied. Ferromagnetic – paramagnetic and metals
– insulator transitions were significantly affected by Mn-site substitution. However, no observable
difference was found in their crystal structure from X-ray diffraction analysis. At room temperature
the structure characterization of these compounds gave the single phase and structure is
the distortion orthorhombic cell with space group symmetry Pnma. The magnetoresistance measurement
showed that the magnetoresistance ratio MR increases until 17% in magnetic field of
0.4 T, and in low magnetic field region (μoH < 0.05 T), MR = 7.5% at 102 K. The investigations
of EPR showed that the intensity of resonance line can be well fitted by the expression: I(T) =
Ioexp(Ea/kBT). The values of activation energy have been determined with Ea = 0.074 eV, 0.093
eV and 0.086 eV for substituted Fe, Co, Ni samples, respectively. These values are slightly smaller
than the value of Ea = 0.12 eV for La0.67Ca0.33MnO3. We attribute the reason to the reduction
of Mn3+ content caused by TM substitution for Mn. The dependence transition temperatures
and transport properties of all samples are well explained by introducing the SE interaction with
considering that the Fe3+, Co3+ and Ni2+ ions have high-spin configuration, the local DOS near
the Fermi level at the TM site Nx(Ef ) would decrease from Ni to Co and Fe [1], thus reduces the
hopping probability and increases the resistivity in order.