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Tang Y.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Tang Y.,Suzhou University | Wang G.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Wang G.,Suzhou University | And 6 more authors.
Rare Metals | Year: 2011

The polycrystalline samples of Pr 0.45(Ca 1-xSr x) 0.55MnO 3 (x = 0.0, 0.2, 0.4, 0.6) were prepared by solid-state reaction. Influence of Sr 2+ substitution for Ca 2+ at A site on magnetism was studied through the measurements of X-ray diffraction (XRD) spectrum, the magnetization-temperature (M-T) curves and electron spin resonance (ESR) curves. The results show that the magnetism strengthens and charge ordering weakens gradually with the increase of Sr 2+ substitution amount, respectively. The transition of paramagnetism(PM)-antiferromagnetism(AFM) occurs below the transition temperature of charge ordering (T CO), and there is little ferromagnetic phase in the antiferromagnetic background at the lower temperature, which results in complex magnetic phases of the samples. Ferromagnetic clusters appear and grow larger with the increase of substitution amount. In addition, the reentrant spin-glass behavior appears at about 41 K. The magnetism phenomenon of the samples is mainly due to the competition between double exchange and Jahn-Teller coupling. The Jahn-Teller coupling becomes weak, and the double exchange wins the advantage in the competition with the increase of substitution amount, which leads to the magnetism variation of the system. amp;© The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg 2011. Source


Tang Y.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Tang Y.,Suzhou University | Wang G.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Wang G.,Suzhou University | And 6 more authors.
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2011

Polycrystalline samples of Pr0.45(Ca1-x Srx)0.55MnO3(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by the solid-state reaction method. Effect of substituting Ca2+ with Sr2+ at A-site on the charge ordering (CO) phase was investigated via the measurements of X-ray diffraction pattern, the magnetization-temperature curve and electron spin resonance spectrum. The results show that the CO phase becomes slight and the CO phase transition temperature TCO decreases gradually with the increase of Sr2+ substituting level. When x≥0.8, the CO phase disappears completely. The bandwidth change caused by substituting Ca2+ with Sr2+ was the main factor for destruction of the CO phase. When x=0.8, the increase of bandwidth caused eg electron delocalization, and the antiferromagnetism decreased and the ferromagnetism increased, causing the disappearance of CO phase. It is indicated that the bandwidth could be adjusted via the substitution of smaller positive ions with larger positive ions in A site, and the increase of the bandwidth could be a effective method for the destruction of CO phase. Source


Tang Y.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Tang Y.,Suzhou University | Wang G.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Wang G.,Suzhou University | And 8 more authors.
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2012

The samples of La 8/9Sr 1/45Na 4/45 MnO 3/0.5x(V 2O 5) (x=0, 0.04, 0.08, 0.012, 0.16, 0.20) were prepared by a solid-state reaction method. The temperature stability of magnetoresistance and electric transport property in the system were investigated via X-ray diffraction (XRD), scanning electron microscopy, resistivity-temperature (ρ-T) and magnetoresistance-temperature (R M-T) measurements. The results show that for all the samples, there is a insulator-metal transition from high temperature range to low temperature range. The insulator-metal transition temperature (T p) shifts to high temperature with increasing V 2O 5 content. Two peaks appear in the ρ-T curves of the samples (x≤0.08) with a low V 2O 5 content, and they vanish in the samples (x≥0.12) with a high V 2O 5 content. The magnetoresistance (R M) of the samples increases with decreasing temprerature in the low temperature range, as a characteristic of low-field magnetoresistance effect. The intrinsic magnetoresistance in the high temperature range decreases with increasing V 2O 5content. The magnetoresistance of the samples of x=0.16 and 0.20 in the temperature range of 319-283K at 0.8T is 6.4% and 5.8%, respectively. The R M temperature stability may be due to the competition between the tunneling magnetoresistance caused by surface phase and the intrinsic magnetoresistance caused by bulk phase. The intrinsic magnetoresistance in bulk phase caused by double exchange dominants in the high temperature range, and the tunneling magnetoresistance caused by interface magnetic disorder dominants in the low temperature range. The R M does not change with temperature in the middle temperature range. Source


Tang Y.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Tang Y.,Suzhou University | Wang G.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Wang G.,Suzhou University | And 7 more authors.
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2014

The polycrystalline samples of La22/27Sr1/27K4/27MnO3 were prepared by a solid-state reaction method at different sintering temperatures. Effect of sintering temperature on the electrical property and magnetoresistance of La22/27Sr1/27K4/27MnO3 was investigated. The results show that the samples prepared at higher sintering temperatures exhibit an abnormal electrical property due to the variation of crystal structure. For magnetoresistance-temperature (RM-T) curves, the RM monotonically increases with the decrease of temperature in the low temperature region, and is the spin-dependent tunneling magnetoresistance of surface phase. The RM peak appears in the high temperature region, which belongs to the intrinsic magnetoresistance of body phase. The RM-T curves of all the samples exhibit a platform in the intermediate temperature region. The magnetoresistance value of the sample sintered at 1373℃ is (7.96±0.08)% in the temperature region of 314-274 K at a magnetic field of 0.8 T, indicating that such a great temperature-indenpendent magnetoresistance in the wide temperature region can favor the practical application of colossal magnetoresistance. The temperature stability of RM is since the perovskite grains are divided into body phase and surface phase, the intrinsic magnetoresistance of body phase dominates in the high temperature region, the tunneling magnetoresistance of surface phase dominates in the low temperature region, and they superimpose in the intermediate temperature region, thus resulting in the temperature-independent magnetoresistance. Source


Tang Y.-G.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Tang Y.-G.,Suzhou University | Wang G.-Y.,Cultivating Base of Anhui Key Laboratory of Spintronics and Nano Materials Research | Wang G.-Y.,Suzhou University | And 7 more authors.
Rare Metals | Year: 2013

The perovskite samples La1-x (Sr1-y K y ) x MnO3 (y = 0.0, 0.2, 04, 0.6, 0.8) were prepared by the solid-state reaction method with comparatively low sintering temperature and with comparatively short sintering time, and the electric transport property and temperature stability of MR of this system were studied. The ρ-T curves show the abnormal phenomenon that with the increase of K doping amount, resistivity increases, and the insulator-metal transition temperature decreases, which is because the influence of the occupation disorder degree of A-site ions σ 2 on the electric transport property of perovskite manganites is larger than that of the radius of A-site ions 〈 r AâŒ. In the temperature range below 225 K, MR increases continuously with the decrease of temperature, which is the characteristic of low-field magnetoresistance; in the comparatively wide temperature range near 250 K, the MR-T curves of all the samples are comparatively flat, and the value of MR almost does not change with temperature, which shows the temperature stability of magnetoresistance, and can be explained by the competition between the low-field magnetoresistance induced by spin-dependent tunneling of surface phase and the intrinsic magnetoresistance of grain phase. The magnetoresistance value of the sample with y = 0.8 keeps at (7.92 ± 0.36) % in the very wide temperature range of 225-275 K, and this is a good reference for the preparation of this kind of sample with practical application value in the future. © 2013 The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg. Source

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