The carbides of NdDy0.2Fe12-yMoyC0.6 （y = 1.5, 2） crystallized in the ThMn12-type structure have been successfully synthesized by arc melting method, followed by a heat treatment. The magnetic properties are strongl...The carbides of NdDy0.2Fe12-yMoyC0.6 （y = 1.5, 2） crystallized in the ThMn12-type structure have been successfully synthesized by arc melting method, followed by a heat treatment. The magnetic properties are strongly enhanced with the addition of carbon. Upon the carbonation the saturation magnetization Ms is increased by about 20emu/g and the Curie temperature Tc is enhanced by 40-70K. The spin reorientation （SR） temperature decreases from 125 K for NdDy0.2Fe10Mo2 to 55 K for NdDy0.2Fe10MO2C0.6 indicating the change of magnetocrystalline anisotropy in the Nd sublattice. It is found that the intrinsic magnetic properties of the carbides can be improved by further nitrogenation, The composite carbon-nitrogen compounds show a Tc - 560K, M8 - 105 emu/g and Ha （anisotropy field） - 86kOe for NdDy0.2Fe10Mo2Co.6Nz and a Tc- 628K, M8 - 119 emu/g and Ha - 115kOe for NdDy0.2Fe10.5Mo1.5C0.6Nz. These magnetic properties are even better than those of simple nitrides, suggesting that these compounds can be considered as a good candidate for permanent magnet applications.展开更多
Molecular dynamics simulation is employed to study structural evolution during compressing low density amorphous ice from one atmosphere to 2.5 GPa. The calculated results show that high density amorphous ice is forme...Molecular dynamics simulation is employed to study structural evolution during compressing low density amorphous ice from one atmosphere to 2.5 GPa. The calculated results show that high density amorphous ice is formed under intermediate pressure of about 1.0GPa and O-O-O angle ranges from about 83°to 113° and O-H…O is bent from 112° to 160°The very high density amorphous ice is also formed under the pressure larger than 1.4 GPa and interstitial molecules are found in 0.3-0.4 A just beyond the nearest O-O distance. Low angle O-H… O disappears and it is believed that these hydrogen bonds are broken or re-bonded under high pressures.展开更多
Ferromagnetic high damping(FHA)alloys with a wide temperature range from-150℃to 300℃have unique application value in extreme environments.In the present work,the damping behaviors of Fe-21 Ga-xLa(x=0.12 wt.%,0.24 wt...Ferromagnetic high damping(FHA)alloys with a wide temperature range from-150℃to 300℃have unique application value in extreme environments.In the present work,the damping behaviors of Fe-21 Ga-xLa(x=0.12 wt.%,0.24 wt.%,0.47 wt.%,1.18 wt.%,and 2.33 wt.%La)alloys have been studied in detail,and a new phenomenological model has been proposed.With the increase of La content,the Laves phase(LaGa_(2))in the matrix increases gradually,and the resistance opposing the domain movement increases as well.Combined with the results of synchrotron radiation X-ray diffraction,neutron diffraction,and magnetic domain observation,the resistance mainly comes from three parts:the average stress related to the lattice distortion of the matrix,the average stress related to the increasing area energy of domain walls(DWs),and the ave rage stress related to the increasing demagnetization energy induced by the Laves phase.Different from the traditional method of reducing internal stress through annealing to improve the damping capacity,the proper internal stress barriers are necessary to Barkhausen jumps to dissipate energy.Therefore,proper doping to balance resistance and mobility of DWs is a reliable way to improve damping capacity.Meanwhile,for Fe-Al and Fe-Cr based Alloys,the new model also has a good fitting effect.This study provides a theoretical and experimental reference for improving the functional properties of ferromagnetic alloys.展开更多
Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated...Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressure- volume （P-V） sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B0 = 369（2） GPa with pressure derivatives of B~ = 4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result （Bo = 351 GPa）, which is close to the recent theoretical calculation result （Bo = 378 GPa）. An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.展开更多
The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound...The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce2NiT-type structure and consists of alternately stacking MgZn2-type NdCo2 and CaCus-type NdCo5 structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μB-1.1 μB and the atomic moment of Nd in the NdCo5 slab is close to the theoretical moment of a free trivalent Nd3＋ ion, whereas the atomic moment of Nd in the NdCo2 slab is much smaller than the theoretical value for a free Nd3＋ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo2 and NdCo5 compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd2Co7 compound.展开更多
利用Rietveld分析方法对钙钛矿锰氧化物La1-xCaxMn0.96Fe0.04O3(x=0.31、0.5、0.6)室温下中子衍射实验数据进行拟合。结果表明,La1-xCaxMn0.96Fe0.04O3化合物具有MnO6八面体,空间群为Pnma,La(Ca)原子占据4c晶位,Mn(Fe)原子占据4b晶位,O...利用Rietveld分析方法对钙钛矿锰氧化物La1-xCaxMn0.96Fe0.04O3(x=0.31、0.5、0.6)室温下中子衍射实验数据进行拟合。结果表明,La1-xCaxMn0.96Fe0.04O3化合物具有MnO6八面体,空间群为Pnma,La(Ca)原子占据4c晶位,Mn(Fe)原子占据4b晶位,O原子分别占据4c和8d晶位。根据拟合结果,计算出Mn O键的键长和Mn O Mn的键角,并对该系列样品结构和磁性能间的关系进行了简单讨论。展开更多
The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powde...The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powder diffraction at room temperature. The results show that the tunneling magnetoresistance of polycrystalline Sr2FeMoO6 depends on its annealing temperature. Annealing at 800 ℃ makes the minimal magnetoresistance(MR) elevated, which may be due to the change of the grain size or the modified intergranular connections. Because of the impurity phase of Fe which probably affects the magnetotransport properties is much larger in sample C, so the MR is decreased by postannealing at 1100 ℃. Therefore, further enhancement of the tunneling magnetoresistance (TMR) can be realized by regulating the grain size at appropriate annealing temperature.展开更多
文摘The carbides of NdDy0.2Fe12-yMoyC0.6 （y = 1.5, 2） crystallized in the ThMn12-type structure have been successfully synthesized by arc melting method, followed by a heat treatment. The magnetic properties are strongly enhanced with the addition of carbon. Upon the carbonation the saturation magnetization Ms is increased by about 20emu/g and the Curie temperature Tc is enhanced by 40-70K. The spin reorientation （SR） temperature decreases from 125 K for NdDy0.2Fe10Mo2 to 55 K for NdDy0.2Fe10MO2C0.6 indicating the change of magnetocrystalline anisotropy in the Nd sublattice. It is found that the intrinsic magnetic properties of the carbides can be improved by further nitrogenation, The composite carbon-nitrogen compounds show a Tc - 560K, M8 - 105 emu/g and Ha （anisotropy field） - 86kOe for NdDy0.2Fe10Mo2Co.6Nz and a Tc- 628K, M8 - 119 emu/g and Ha - 115kOe for NdDy0.2Fe10.5Mo1.5C0.6Nz. These magnetic properties are even better than those of simple nitrides, suggesting that these compounds can be considered as a good candidate for permanent magnet applications.
基金Supported by the National Natural Science Foundation of China under Grand No 10474085.
文摘Molecular dynamics simulation is employed to study structural evolution during compressing low density amorphous ice from one atmosphere to 2.5 GPa. The calculated results show that high density amorphous ice is formed under intermediate pressure of about 1.0GPa and O-O-O angle ranges from about 83°to 113° and O-H…O is bent from 112° to 160°The very high density amorphous ice is also formed under the pressure larger than 1.4 GPa and interstitial molecules are found in 0.3-0.4 A just beyond the nearest O-O distance. Low angle O-H… O disappears and it is believed that these hydrogen bonds are broken or re-bonded under high pressures.
基金supported financially by the National Natural Science Foundation of China(No.51971212)the Russian Science Foundation(No.19-72-20080)。
文摘Ferromagnetic high damping(FHA)alloys with a wide temperature range from-150℃to 300℃have unique application value in extreme environments.In the present work,the damping behaviors of Fe-21 Ga-xLa(x=0.12 wt.%,0.24 wt.%,0.47 wt.%,1.18 wt.%,and 2.33 wt.%La)alloys have been studied in detail,and a new phenomenological model has been proposed.With the increase of La content,the Laves phase(LaGa_(2))in the matrix increases gradually,and the resistance opposing the domain movement increases as well.Combined with the results of synchrotron radiation X-ray diffraction,neutron diffraction,and magnetic domain observation,the resistance mainly comes from three parts:the average stress related to the lattice distortion of the matrix,the average stress related to the increasing area energy of domain walls(DWs),and the ave rage stress related to the increasing demagnetization energy induced by the Laves phase.Different from the traditional method of reducing internal stress through annealing to improve the damping capacity,the proper internal stress barriers are necessary to Barkhausen jumps to dissipate energy.Therefore,proper doping to balance resistance and mobility of DWs is a reliable way to improve damping capacity.Meanwhile,for Fe-Al and Fe-Cr based Alloys,the new model also has a good fitting effect.This study provides a theoretical and experimental reference for improving the functional properties of ferromagnetic alloys.
基金Acknowledgments This work has benefited from the use of 1） Los Alamos Neutron Science Facility at Los Alamos National Laboratory and 2） ISIS Pulsed Neutron and Muon Source at Rutherford-Appleton Laboratory. The financial support of the National Science Foundation＇s 1） International Materials Institutes （IMI） under DMR-0231320, 2） Integrative Graduate Education and Research Training （IGERT） under DGE-9987548, 3） Combined Research and Curriculum Development （CRCD） under EEC-9527527 and EEC-0203415, and 4） Major Research Instrumentation （MRI） under DMR-0231320 at the University of Tennessee with Dr HUBER C, Dr Van HARTESVELDT C J, Dr DUTTA D, Dr JENNINGS W, Dr G0LDBERG L, Ms P0ATS M, and Dr B0ULDIN C R as the Program Directors, is greatly appreciated. Additional funding for this project was gratefully received from the Tennessee Advanced Materials Laboratory, with Prof. PLUMMER E W as the Director.
基金Project supported by the Research Foundation of Key Laboratory of Neutron Physics(Grant No.2015BB03)the National Natural Science Foundation of China(Grant Nos.11774247)+2 种基金the Science Foundation for Excellent Youth Scholars of Sichuan University(Grant No.2015SCU04A04)the Joint Usage/Research Center PRIUS(Ehime University,Japan)Chinese Academy of Sciences(Grant No.2017-BEPC-PT-000568)
文摘Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressure- volume （P-V） sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B0 = 369（2） GPa with pressure derivatives of B~ = 4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result （Bo = 351 GPa）, which is close to the recent theoretical calculation result （Bo = 378 GPa）. An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.
基金supported by the National Natural Science Foundation of China (Grant No. 50631040)the National Basic Research Program of China (Grants Nos. 2006CB601101 and 2006CB605101)
文摘The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce2NiT-type structure and consists of alternately stacking MgZn2-type NdCo2 and CaCus-type NdCo5 structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μB-1.1 μB and the atomic moment of Nd in the NdCo5 slab is close to the theoretical moment of a free trivalent Nd3＋ ion, whereas the atomic moment of Nd in the NdCo2 slab is much smaller than the theoretical value for a free Nd3＋ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo2 and NdCo5 compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd2Co7 compound.
文摘利用Rietveld分析方法对钙钛矿锰氧化物La1-xCaxMn0.96Fe0.04O3(x=0.31、0.5、0.6)室温下中子衍射实验数据进行拟合。结果表明,La1-xCaxMn0.96Fe0.04O3化合物具有MnO6八面体,空间群为Pnma,La(Ca)原子占据4c晶位,Mn(Fe)原子占据4b晶位,O原子分别占据4c和8d晶位。根据拟合结果,计算出Mn O键的键长和Mn O Mn的键角,并对该系列样品结构和磁性能间的关系进行了简单讨论。
基金Project(1998061304) supported by the National Natural Foundation of China
文摘The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powder diffraction at room temperature. The results show that the tunneling magnetoresistance of polycrystalline Sr2FeMoO6 depends on its annealing temperature. Annealing at 800 ℃ makes the minimal magnetoresistance(MR) elevated, which may be due to the change of the grain size or the modified intergranular connections. Because of the impurity phase of Fe which probably affects the magnetotransport properties is much larger in sample C, so the MR is decreased by postannealing at 1100 ℃. Therefore, further enhancement of the tunneling magnetoresistance (TMR) can be realized by regulating the grain size at appropriate annealing temperature.
