Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties, especially their interesting hard magnetic properties. In this paper, we have summarized the ...Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties, especially their interesting hard magnetic properties. In this paper, we have summarized the magnetic and structural properties of Mn-based intermetallic compounds（Mn X, where X = Al, Bi, and Ga）. Various methods for synthesizing single phases of MnAl, MnBi, and Mnx Ga were developed in our lab. A very high saturation magnetization of 125 emu/g,coercivity of 5 kOe, and maximum energy product（BH）max of 3.1 MG·Oe were achieved at room temperature for the pure τ-Mn–Al magnetic phase without carbon doping and the extrusion process. Low temperature phase（LTP） MnBi with a purity above 95 wt.% can be synthesized. An abnormal temperature coefficient of the coercivity was observed for the LTP MnBi magnet. Its coercivity increased with temperature from 100 K to 540 K, reached a maximum of 2.5 T at about540 K, and then decreased slowly to 1.8 T at 610 K. The positive temperature coefficient of the coercivity is related to the evolution of the structure and magnetocrystalline anisotropy field of the LTP MnBi phase with temperature. The LTP MnBi bonded magnets show maximum energy products（BH）max of 8.9 MG·Oe（70 kJ/m^3） and 5.0 MG·Oe（40 k J/m^3） at room temperature and 400 K, respectively. Ferrimagnetic Mnx Ga phases with L10 structures（x 〈 2.0） and D022 structures（x 〉 2.0） were obtained. All of the above structures can be described by a D0（22） supercell model in which 2 a-Ga and 2 b-Mn are simultaneously substituted. The tetragonal D0（22） phases of the Mnx Ga show high coercivities ranging from 7.2 kOe for low Mn content x = 1.8 to 18.2 kOe for high Mn content x = 3 at room temperature. The Mn（1.2） Ga sample exhibits a room temperature magnetization value of 80 emu/g. The hard magnetic properties of coercivityiHc = 3.5 kOe, remanence Mr = 43.6 emu/g, and（BH）max = 2.5 MG·Oe were obtained at room temperature. Based on the above studies, we believe that Mn-based magnetic materials could be promising candidates for rare earth free permanent magnets exhibiting a high Curie temperature, high magnetocrystalline anisotropy, and very high coercivity.展开更多
A series of deuterated ammonium dihydrogen phosphate(DADP) crystals were grown and their structures were investigated by using powder neutron diffraction method. In the entire composition range, the deuterated level i...A series of deuterated ammonium dihydrogen phosphate(DADP) crystals were grown and their structures were investigated by using powder neutron diffraction method. In the entire composition range, the deuterated level in the crystals is lower compared with the aqueous growth solution. The deuterium segregation coefficient in the crystals decreases with increasing deuterium content of the solution. The deuterium content in the NH_4^+ group is higher than that in H_2PO_4^- group.In addition, the variations of lattice parameters are shown here.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
We use neutron powder diffraction to study the non-superconducting phases of ThFeAsN1-xOx with x = 0.15,0.6.In our previous results of the superconducting phase ThFeAsN with Tc = 30 K,no magnetic transition is observe...We use neutron powder diffraction to study the non-superconducting phases of ThFeAsN1-xOx with x = 0.15,0.6.In our previous results of the superconducting phase ThFeAsN with Tc = 30 K,no magnetic transition is observed by cooling down to 6 K,and possible oxygen occupancy at the nitrogen site is shown in the refinement[Europhys.Lett.117(2017)57005].Here in the oxygen doped system ThFeAsN1-xOx,two superconducting regions(0≤x≤0.1 and 0.25≤x≤0.55)are identified by transport experiments[J.Phys.:Condens.Matter30(2018)255602].However,within the resolution of our neutron powder diffraction experiment,neither the intermediate doping x= 0.15 nor the heavily overdoped compound x = 0.6 shows any magnetic order from 300 K to 4 K.Therefore,while it shares the common phenomenon of two superconducting domes as most 1111-type iron-based superconductors,the magneticall.y ordered parent compound may not exist in this nitride family.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51731001,11805006,51371009,11504348,and 11675006)National Key Research and Development Program of China(Grant Nos.2016YFB0700901,2017YFA0401502,and 2017YFA0206303)
文摘Mn-based intermetallic compounds have attracted much attention due to their fascinating structural and physical properties, especially their interesting hard magnetic properties. In this paper, we have summarized the magnetic and structural properties of Mn-based intermetallic compounds（Mn X, where X = Al, Bi, and Ga）. Various methods for synthesizing single phases of MnAl, MnBi, and Mnx Ga were developed in our lab. A very high saturation magnetization of 125 emu/g,coercivity of 5 kOe, and maximum energy product（BH）max of 3.1 MG·Oe were achieved at room temperature for the pure τ-Mn–Al magnetic phase without carbon doping and the extrusion process. Low temperature phase（LTP） MnBi with a purity above 95 wt.% can be synthesized. An abnormal temperature coefficient of the coercivity was observed for the LTP MnBi magnet. Its coercivity increased with temperature from 100 K to 540 K, reached a maximum of 2.5 T at about540 K, and then decreased slowly to 1.8 T at 610 K. The positive temperature coefficient of the coercivity is related to the evolution of the structure and magnetocrystalline anisotropy field of the LTP MnBi phase with temperature. The LTP MnBi bonded magnets show maximum energy products（BH）max of 8.9 MG·Oe（70 kJ/m^3） and 5.0 MG·Oe（40 k J/m^3） at room temperature and 400 K, respectively. Ferrimagnetic Mnx Ga phases with L10 structures（x 〈 2.0） and D022 structures（x 〉 2.0） were obtained. All of the above structures can be described by a D0（22） supercell model in which 2 a-Ga and 2 b-Mn are simultaneously substituted. The tetragonal D0（22） phases of the Mnx Ga show high coercivities ranging from 7.2 kOe for low Mn content x = 1.8 to 18.2 kOe for high Mn content x = 3 at room temperature. The Mn（1.2） Ga sample exhibits a room temperature magnetization value of 80 emu/g. The hard magnetic properties of coercivityiHc = 3.5 kOe, remanence Mr = 43.6 emu/g, and（BH）max = 2.5 MG·Oe were obtained at room temperature. Based on the above studies, we believe that Mn-based magnetic materials could be promising candidates for rare earth free permanent magnets exhibiting a high Curie temperature, high magnetocrystalline anisotropy, and very high coercivity.
基金Project supported by the National Natural Science Foundation of China(Grant No.51402173)Shandong Provincial Natural Science Joint Foundation with Universities and Scientific Research Institution,China(Grant No.ZR2017LEM006)+1 种基金the Neutron Physics Laboratory,China Academy of Engineering Physics(Grant No.2014BB07)the Fundamental Research Funds for Central Universities,China(Grant No.FRF-TP-15-099A1)
文摘A series of deuterated ammonium dihydrogen phosphate(DADP) crystals were grown and their structures were investigated by using powder neutron diffraction method. In the entire composition range, the deuterated level in the crystals is lower compared with the aqueous growth solution. The deuterium segregation coefficient in the crystals decreases with increasing deuterium content of the solution. The deuterium content in the NH_4^+ group is higher than that in H_2PO_4^- group.In addition, the variations of lattice parameters are shown here.
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 Strategic Priority Research Program of Chinese Academy of Sciences under Grant Nos XDB07020300and XDB25000000the National Key Research and Development Program of China under Grant Nos 2017YFA0303103,2017YFA0302903 and 2016YFA0300502+3 种基金the National Natural Science Foundation of China under Grant Nos 11374011,11504347,11304183,11674406 and 11822411the Youth Innovation Promotion Association of Chinese Academy of Sciences under Grant No2016004the Key Laboratory of Neutron Physics of CAEP under Grant No 2015AB03the Science Challenge Project under Grant No TZ2016004
文摘We use neutron powder diffraction to study the non-superconducting phases of ThFeAsN1-xOx with x = 0.15,0.6.In our previous results of the superconducting phase ThFeAsN with Tc = 30 K,no magnetic transition is observed by cooling down to 6 K,and possible oxygen occupancy at the nitrogen site is shown in the refinement[Europhys.Lett.117(2017)57005].Here in the oxygen doped system ThFeAsN1-xOx,two superconducting regions(0≤x≤0.1 and 0.25≤x≤0.55)are identified by transport experiments[J.Phys.:Condens.Matter30(2018)255602].However,within the resolution of our neutron powder diffraction experiment,neither the intermediate doping x= 0.15 nor the heavily overdoped compound x = 0.6 shows any magnetic order from 300 K to 4 K.Therefore,while it shares the common phenomenon of two superconducting domes as most 1111-type iron-based superconductors,the magneticall.y ordered parent compound may not exist in this nitride family.
