[Establishment and melting of charge ordering in La0.3Ca0.7Mn(1-x)W(x)O3 system].

Polycrystalline samples of La0.3Ca0.7Mn(1-x)W(x)O3 (0.00 < or = x < or = 0.15) were prepared by conventional solid-state reaction method. The influence of W doping at Mn site on the magnetic transition of La0.3Ca0.7Mn(1-x)W(x)O3 system was studied by the measurements of magnetization-temperature (MT) curves, magnetization-magnetic intensity (MH) curves, and ESR spectra. The results show that, with the increase in W doping amount, the magnetic transition of the system exhibits a complicated charge process, when the doping amount is 0.00 < or = x < or = 0.08, the charge-ordering (CO) phase exists in the system, AFM/CO states coexist below the transition temperature, and the charge-ordering temperature (Tco) goes up with the increase in W doping content; when x > or = 0.12, the charge ordering (CO) state of the system weakens and melts, and paramagnetism-ferromagnetism (PM-FM) transition exists at extremely low temperature.

[Magnetic properties and transport behaviors in double doped La(0.67+1.33x)Sr(0.33-1.33x)Mn(1-x)Mg(x)O3 system].

The M-T curves, M-H curves, ESR curves, infrared spectrum, Raman spectrum, rho-T curves and MR-T curves of La(0.67+1.33x)Sr(0.33-1.33x)Mn(1-x)Mg(x)O3 (0.00 < or = x < or = 0.25) were studied. The experiment pointed out that all samples exhibit a paramagnetic-ferromagnetic (PM-FM) transition associated with metallic-insulating (MI) transition in the low doping region, which does not occur in the heavy doping zone. The authors suggest that this behavior is attributed to the difference between the Jahn-Teller distortion of the Mn3+ ion neighboring Mg2+ and that of the Mn3+ ion non-neighboring Mg2+, which is confirmed by the IR and Raman spectra. The anomalous transport behavior is dominated by the differerent Jahn-Teller distortion.

[Phase separation and transport behaviors in La(0.7 - x)Dy(x)Sr0.3MnO3 system].

The influence of Dy doping (0.00 < or = x < or = 0.30) on magnetic and electric properties of La0.7Sr0.3MnO3 was studied by measuring M-T curves, M-H curves, ESR curves, rho-T curves and MR-T curves of the samples. The experimental results indicate that all samples undergo the transition from paramagnetism to ferromagnetism at T(C). When T < T(C), the doped samples enter the cluster-spin glass state, and the antiferromagnetism is exhibited at lower temperature. For the samples x = 0.2, the phase separation occurs at the temperature far above T(C), the variation in magnetic structure caused by Dy doping leads to colossal magnetoresistance.