Nguyen Thi Dung

Tuning the magnetic phase transition and the magnetocaloric properties of La0.7Ca0.3MnO3 compounds through Sm-doping

In this work, we point out that the width and the nature of the magnetic phase transition, TC value, and as well as magnetocaloric effect in La0.7-xSmxCa0.3MnO3 compounds can be easily modified through Sm-doped into La-site. With an increasing Sm concentration, a systematic decrease in the magnetization, TC, and magnetic entropy change (ΔSm) are observed. The Arrott-plot proveds that the samples with x = 0 and 0.1 undergoing a first-order phase transition. Meanwhile, sample x = 0.2 undergoes a second-order phase transition, which exhibits a high value of the relative cooling power (81.5 J/kg at ΔH = 10 kOe). An analysis of the critical behavior based on the modified Arrott plots method has been done for sample x = 0.2. The results proved a coexistence of the long- and short-range interactions in La0.5Sm0.2Ca0.3MnO3 compound.

Paleomagnetism of upper permian basaltic rocks of Cam Thuy formation from Thuan Chau locality, Son La, Northwest Vietnam

Oriented-core samples (74) from eight sites collected from the Late Permian basaltic Cam Thuy formation exposed at Thuan Chau locality, Son La Province, northwestern Vietnam yield interpretable magnetizations in progressive demagnetization. The characteristic remanent magnetization (ChRM) components carried by magnetite and hematite are successfully isolated from secondary components reveal a mean, stratigraphic coordinates paleomagnetic direction of Ds = 216.1, Is = 10.5 (α95 = 8.9, k = 107.8, N = 7 site mean directions), corresponding to a virtual geomagnetic pole located at λ = 45.6 N, = 226.8 E and a paleolatitude for the study area situated at ±5.3 N during the Late Permian. A comparison of the pole we report in this study with the Late Permian pole of South China Block shows that this basaltic terrane of northwest Vietnam has been close to if not a coherent part of the South China Block since Late Permian. This result implies that insignificant cumulative displacement has occurred along the Ailao Shan/Red River fault system during the Cenozoic India-Eurasia collision. ©2015 Vietnam Academy of Science and Technology

Magnetocaloric effect and the change from first- to second-order magnetic phase transition in Pr0.7CaxSr0.3-xMnO3 polycrystalline compounds

The work presents the magnetocaloric effect and critical behavior of monoclinic polycrystalline Pr0.7CaxSr0.3-xMnO3 prepared by solid state reaction. The ferromagnetic-paramagnetic phase transition temperature decreases from 267, 202, 138 to 126 K with increasing doping concentration from x=0 to 0.3. The maximum values of entropy change appear near the transition phase points and were found to be 6.4, 7.2, 3.9 and 4.0 J.kg-1.K-1 with 5 Tesla of field change for x=0-0.3, respectively. However, the shift to the higher temperature side with the increasing field change was observed clearly in sample x=0.1. Besides, the considering magnetic phase transition of samples based on Banerjee’s criterion showed a first-order phase transition in Pr0.7Ca0.1Sr0.2MnO3 (x=0.1) while samples with x=0, x=0.2 and 0.3 exhibited a second-order phase transition.The work presents the magnetocaloric effect and critical behavior of monoclinic polycrystalline Pr0.7CaxSr0.3-xMnO3 prepared by solid state reaction. The ferromagnetic-paramagnetic phase transition temperature decreases from 267, 202, 138 to 126 K with increasing doping concentration from x=0 to 0.3. The maximum values of entropy change appear near the transition phase points and were found to be 6.4, 7.2, 3.9 and 4.0 J.kg-1.K-1 with 5 Tesla of field change for x=0-0.3, respectively. However, the shift to the higher temperature side with the increasing field change was observed clearly in sample x=0.1. Besides, the considering magnetic phase transition of samples based on Banerjee’s criterion showed a first-order phase transition in Pr0.7Ca0.1Sr0.2MnO3 (x=0.1) while samples with x=0, x=0.2 and 0.3 exhibited a second-order phase transition.