The crystallization and properties of alloys with Fe partly substituted by Cr and Cu fully substituted by Au in Finemet

Title: The crystallization and properties of alloys with Fe partly substituted by Cr and Cu fully substituted by Au in Finemet
Authors: N.Q. Hoa
N. Chau
S.-C. Yu
Keywords: nanocrystalline alloy
soft magnetic amorphous system
magnetocaloric effect
Issue Date: 2007
Publisher: ELSEVIER SCIENCE SA, PO BOX 564, 1001 LAUSANNE, SWITZERLAND
Citation: ISIKNOWLEDGE
Abstract: The structure, crystallization and magnetic properties of ribbons obtained by first making amorphous ribbons and then objecting them to a crystallization annealing have been published elsewhere by us previously. In the present work the soft magnetic ribbons Fe73.5-xCrxSi13.5B9Nb3Au1 (numbers indicate at.%, x = 1-5) are prepared by fast quenching on a single copper wheel. X-ray diffraction patterns show that the as-cast samples are amorphous. Differential scanning calorimetry analysis indicates that the crystallization temperature of the alpha-Fe(Si) phase is a little higher than that of pure Finemet. With the same annealing conditions, the crystallization volume fraction decreases with increasing Cr content substituted for Fe. Hysteresis loops of as-cast samples measured by Permagraph show that domain walls are pinned. After appropriate annealing, the ultrasoft magnetic properties of nanocomposite materials are established. The magnetic entropy change, vertical bar Delta S-m vertical bar, of studied samples has been determined, and a giant magnetocaloric effect is found. Our materials could be considered as promising magnetic refrigerants working at high temperatures (several hundreds degrees C). (c) 2006 Elsevier B.V. All rights reserved.
Description: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Volume: 449 Pages: 364-367 Published: MAR 25 2007 ; TNS07635
URI: http://repository.vnu.edu.vn/handle/VNU_123/31437
ISSN: 0921-5093
Appears in Collections: Bài báo của ĐHQGHN trong Web of Science

The discovery of the colossal magnetocaloric effect in a series of amorphous ribbons based on Finemet

Title: The discovery of the colossal magnetocaloric effect in a series of amorphous ribbons based on Finemet
Authors: N. Chau
N.D. The
N.Q. Hoa
Keywords: amorphous magnetic materials
magnetocaloric effect
nanocrystalline materials
Issue Date: 2007
Publisher: ELSEVIER SCIENCE SA, PO BOX 564, 1001 LAUSANNE, SWITZERLAND
Citation: ISIKNOWLEDGE
Abstract: A large number of amorphous ribbons based on Finemet have been prepared by rapid quenching on a single copper wheel with linear speed of v = 25-30 m/s. The ribbons are 20-25 mu m thick and 6-8 mm wide. All as-cast samples are amorphous. Two criteria producing the colossal magnetocaloric effect (CMCE) in magnetic materials working as magnetic refrigerants are high saturation magnetization and sharp ferromagnetic-paramagnetic phase transition. The Fe-based amorphous ribbons fit these cretia. Thermomagnetic curves as well as isothermal magnetization curves around the Curie temperature of all the studied samples have been determined. The results show that the magnetic entropy change, vertical bar Delta S-m vertical bar, belongs to a class of materials with CMCE and the vertical bar Delta S-m vertical bar(max) values have been obtained at a moderately low magnetic field change of 1.35 T, moreover vertical bar Delta S-m vertical bar(max) occurred at quite high temperature. (c) 2006 Elsevier B.V. All rights reserved.
Description: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Volume: 449 Pages: 360-363 Published: MAR 25 2007 ; TNS07634
URI: http://repository.vnu.edu.vn/handle/VNU_123/31436
ISSN: 0921-5093
Appears in Collections: Bài báo của ĐHQGHN trong Web of Science

Magnetic properties of half-metallic semi Heusler Co1-xCuxMnSb compounds

Title: Magnetic properties of half-metallic semi Heusler Co1-xCuxMnSb compounds
Authors: N.P. Duong
L.T. Hung
T.D. Hien
Keywords: Co1-xCuxMnSb
Heusler alloys
half-metals
ferromagnets
localized electrons
itinerant electrons
Issue Date: 2007
Publisher: ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS
Citation: ISIKNOWLEDGE
Abstract: A study of the half-metallic character of the semi Hensler alloys Co1-xCuxMnSb (0 <= x <= 0.9) is presented. We investigated the saturation magnetization M-S at temperatures from 5 K to room temperature and the temperature dependence of the DC magnetic susceptibility y above Curie temperature T-C. The magnetic moments at 5 K, for most compositions are very close to the quantized value of 4 mu(B) for Mn3+ ion, the compound with 90% Co substituted by Cu is still ferromagnetic with M-S (5K) = 3.78 mu(B)/f.u. These results emphasize the role of Co atoms in maintaining the ferromagnetic order in the material. The Curie temperature is decreased from 476 K to about 300 K as the Cu content increases from 0% to 90%. Above T-C, the chi(-1) vs T curves follow very well the Curie-Weiss law. The effective moment mu(eff) and paramagnetic Curie temperature theta are derived. A comparison between the values of M-S at 5 K and mu(eff) shows a transition from localized to itinerant spin system in these compounds. (C) 2006 Elsevier B.V. All rights reserved.
Description: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Volume: 311 Issue: 2 Pages: 605-608 Published: APR 2007 ; TNS07633
URI: http://repository.vnu.edu.vn/handle/VNU_123/31435
ISSN: 1873-4766
0304-8853
Appears in Collections: Bài báo của ĐHQGHN trong Web of Science

Sulfurospirillum cavolei sp nov, a facultatively anaerobic sulfur-reducing bacterium isolated from an underground crude oil storage cavity

Title: Sulfurospirillum cavolei sp nov, a facultatively anaerobic sulfur-reducing bacterium isolated from an underground crude oil storage cavity
Authors: Yumiko Kodama
Le Thu Ha
Kazuya Watanabe
Keywords: DEHALOSPIRILLUM-MULTIVORANS
GEN-NOV
STRAINS
Issue Date: 2007
Publisher: SOC GENERAL MICROBIOLOGY, MARLBOROUGH HOUSE, BASINGSTOKE RD, SPENCERS WOODS, READING RG7 1AG, BERKS, ENGLAND
Citation: ISIKNOWLEDGE
Abstract: A novel facultatively anaerobic sulfur-reducing bacterium, designated strain Phe91(T), was isolated from petroleum-contaminated groundwater in an underground crude oil storage cavity at Kuji in Iwate, Japan. Cells of strain Phe91(T) were slightly curved rods with single polar flagella. Optimum growth was observed at pH 7.0 and 30 degrees C, The novel strain utilized elemental sulfur, thiosulfate, sulfite, dithionite, arsenate, nitrate and DMSO as electron acceptors with lactate as an energy and carbon source, but nitrite was not utilized. Microaerophilic growth was also observed. Fumarate, pyruvate, lactate, malate, succinate, hydrogen (with acetate as a carbon source) and formate (with acetate) could serve as electron donors. Fumarate, pyruvate and malate were fermented. The DNA G + C content was 42.7 mol%. On the basis of 16S rRNA gene sequence phylogeny, strain Phe91(T) was affiliated with the genus Sulfurospirillum in the class Epsilonproteobacteria and was most closely related to Sulfurospirillum deleyianum (sequence similarity 97%). However, the DNA-DNA hybridization value between strain Phe91(T) and S. deleyianum was only 14 %. Based on the physiological and phylogenetic data, Phe91(T) should be classified as a representative of a novel species in the genus Suffurospirillum; the name Sulfurospirillum cavolei sp. nov. is proposed, with Phe91(T) (=JCM 13918(T) = DSM 18149(T)) as the type strain.
Description: INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY Volume: 57 Pages: 827-831 Part: 4 Published: APR 2007 ; TNS07632
URI: http://repository.vnu.edu.vn/handle/VNU_123/31434
ISSN: 1466-5026
Appears in Collections: Bài báo của ĐHQGHN trong Web of Science