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Tran Dang Thanh,Phan, T. L.,Phung Quoc Thanh,Hoang Nam Nhat,Duong Anh Tuan,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.6
<P>This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of La0.7Ca0.3Mn1-xCoxO3(x = 0.09-0.17) prepared by solid-state reaction. Magnetic measurements versus temperature revealed a gradual decrease of the magnetization (M) and Curie temperature (T-C) with increasing Co concentration (x). The T-C values vary from 194 to 159 K as changing x from 0.09 to 0.17, respectively. H/M versus M-2 performances around T-C prove the x = 0.09 sample undergoing a first-order magnetic phase transition (FOMT) while the samples with x >= 0.11 undergo a second-order magnetic phase transition (SOMT). The other with x = 0.10 is considered as a threshold concentration of the FOMT-SOMT transformation. Considering temperature dependences of resistivity, rho(T), in the presence and absence of the magnetic field, the samples (excepting for x = 0.17) exhibit a metal-insulator transition at T (P) = 60-160 K, which shifts toward lower temperatures with increasing x. In the metallic-ferromagnetic region, the rho(T) data are well fitted to a power function rho(T) = rho(0) + rho(2) T-2 + rho(4.5) T-4.5. This indicates electron-electron and electron-magnon scattering processes are dominant at temperatures T < T (P). In addition, the conduction data at temperatures T > theta(D)/2 (theta(D) is the Debye temperature) and T (P) < T < theta(D)/2 obey the small-polaron and variable-range hopping models, respectively. The values of activation energy E-p, and density of states at the Fermi level N(E-F) were accordingly determined. Here, N(E-F) increases while E-p decreases when an external magnetic field is applied. We also have found that N(E-F) increases when materials transfer from the FOMT to the SOMT, and N(E-F) value becomes smallest for the sample having the coexistence of the FOMT and SOMT (i.e., x = 0.10).</P>
Conventional and inverse magnetocaloric effects, and critical behaviors in Ni43Mn46Sn8In3 alloy
Tran Dang Thanh,W.Z. Nan,Gnu Nam,Hoang Thanh Van,유태수,판더롱,S. C. Yu 한국물리학회 2015 Current Applied Physics Vol.15 No.10
A systematic study of the conventional and inverse magnetocaloric effects, and critical behaviors in an alloy ingot of Ni43Mn46Sn8In3 has been performed. Our results reveal the sample exhibiting structural and magnetic phase transitions at temperatures TC M = 166 K (TC of the martensitic phase), TM-A =260 K (the martensitic-to-austenitic phase transformation) and TC A = 296 K (TC of the austenitic phase). The large values of refrigerant capacity (RC) around TMeA and TC A are found to be RCM-A = 172.6 and RCA = 155.9 J kg-1, respectively, under an applied field change of 30 kOe. Our critical analyses near the TC M and TC A reveal that a coexistence of the long- and short-range ferromagnetic order in the martensitic phase, while the long-range ferromagnetic order exists in the austenitic phase. Interestingly, at around TC A, the maximum magnetic entropy change (|ΔSmax|) versus magnetic field H obeys a power law, |ΔSmax| = a·Hn, where the exponent n is found to be about 0.66.