We report on the structural transformation and unique magnetic properties of manganese nitrides prepared by nitriding Mn under N_(2) pressures of up to 25 MPa with varying temperatures.High N_(2) pressure not only mak...We report on the structural transformation and unique magnetic properties of manganese nitrides prepared by nitriding Mn under N_(2) pressures of up to 25 MPa with varying temperatures.High N_(2) pressure not only makes nitridation more efficient at lower temperatures,but also enhances the N-content in the nitride lattices,which were expanded with increasing N-content.The N-rich nitrides,includingε-Mn_(4)N,ζ-Mn6N_(2).58 andη-Mn_(3)N_(2),exhibit unique thermal behaviors.The N-richε-phase exhibits much larger coercivity and lower saturation magnetization in comparison with theε-phase prepared under ambient N_(2) pressures.The coercivity of the N-richζ-phase reaches up to 45054 A/m.A saturation magnetization as large as 31 Am^(2)/kg is observed in the N-richη-phase.Both are quite different from the conventional antiferromagneticζ-andη-phase obtained under ambient N_(2) pressures.We ascribe the unconventional magnetic properties of the nitrides to the lattice distortion originating from the N-enrichment.展开更多
We report the phenomenon of size segregation and the experimental evidence for the presence of correlated areas mediated by dipolar interactions in three-dimensional Fe nanoparticle assemblies.Iron nanoparticles dispe...We report the phenomenon of size segregation and the experimental evidence for the presence of correlated areas mediated by dipolar interactions in three-dimensional Fe nanoparticle assemblies.Iron nanoparticles dispersed in ethanol assemble into tabular whiskers (8 μm × 40 μm in cross section with lengths up to 1 0 cm) due to dipolar interactions.Magnetic force microscopy observations on iron nanoparticle compact assemblies prove the local magnetic correlation of the Fe nanoparticles due to dipolar coupling and the formation of domain-like structures in expanded dimensions.Magnetic measurements show that the coercivity and the low field magnetic susceptibility of the Fe nanoparticle assemblies increase while the saturation magnetization decreases with the increasing interparticle distance.展开更多
We report on an order-reversed quenching phenomenon in manganese nitrides under flash melting,which prevents the thermodynamically favorable phase transformations from occurring at high temperatures by providing a nar...We report on an order-reversed quenching phenomenon in manganese nitrides under flash melting,which prevents the thermodynamically favorable phase transformations from occurring at high temperatures by providing a narrow window of time.The Mn-N kept un-decomposed at high temperatures generated by current up to 339 MA/m^(2) within 60 ms.After flash melting,the Mn-N shows a significantly enhanced coercivity and a decreased crystalline size.The Mn-N samples decompose rapidly at temperatures above 1100 K with time.The order-reversed quenching technique is potentially useful in processing and preventing phase transformations of meta-stable materials at high temperatures.展开更多
Two kinds of Nd 1+ x Ba 2- x Cu 3O 7- δ , the sintered samples and zone melted samples, were treated in pure Ar at 950 ℃. The substitution of Nd ions for Ba ions in the Nd 1+ x Ba 2- ...Two kinds of Nd 1+ x Ba 2- x Cu 3O 7- δ , the sintered samples and zone melted samples, were treated in pure Ar at 950 ℃. The substitution of Nd ions for Ba ions in the Nd 1+ x Ba 2- x Cu 3O 7- δ before and after the heat treatment was investigated by XRD. In order to know the effects of heat treatment, the T c and J c of samples with and without the heat treatment in Ar were comparatively studied. The results show that the substitution of Nd for Ba decreases, whereas T c and J c increase after the treatment. The Nd 1+ x Ba 2- x Cu 3O 7- δ samples were oxygenated in pure oxygen at 300 ℃ . Based on the XRD spectra it was found that the samples with x <0.4 can transform from tetragonal phase into orthorhombic phase after the oxygenation, whereas in the sample with x >0.4 no phase transition occurs even after a long time oxygenation.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874159,11074227,21101143Zhejiang Provincial Natural Science Foundation(No R6110362)Zhejiang Provincial Innovation Team Project(No 2010R50016).
文摘We report on the structural transformation and unique magnetic properties of manganese nitrides prepared by nitriding Mn under N_(2) pressures of up to 25 MPa with varying temperatures.High N_(2) pressure not only makes nitridation more efficient at lower temperatures,but also enhances the N-content in the nitride lattices,which were expanded with increasing N-content.The N-rich nitrides,includingε-Mn_(4)N,ζ-Mn6N_(2).58 andη-Mn_(3)N_(2),exhibit unique thermal behaviors.The N-richε-phase exhibits much larger coercivity and lower saturation magnetization in comparison with theε-phase prepared under ambient N_(2) pressures.The coercivity of the N-richζ-phase reaches up to 45054 A/m.A saturation magnetization as large as 31 Am^(2)/kg is observed in the N-richη-phase.Both are quite different from the conventional antiferromagneticζ-andη-phase obtained under ambient N_(2) pressures.We ascribe the unconventional magnetic properties of the nitrides to the lattice distortion originating from the N-enrichment.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874159,11074227 and 50801039Zhejiang Natural Science Foundation(R6110362)the Fundamental R&D Program for Core Technology of Materials by the Ministry of Knowledge Economy,R.Korea.
文摘We report the phenomenon of size segregation and the experimental evidence for the presence of correlated areas mediated by dipolar interactions in three-dimensional Fe nanoparticle assemblies.Iron nanoparticles dispersed in ethanol assemble into tabular whiskers (8 μm × 40 μm in cross section with lengths up to 1 0 cm) due to dipolar interactions.Magnetic force microscopy observations on iron nanoparticle compact assemblies prove the local magnetic correlation of the Fe nanoparticles due to dipolar coupling and the formation of domain-like structures in expanded dimensions.Magnetic measurements show that the coercivity and the low field magnetic susceptibility of the Fe nanoparticle assemblies increase while the saturation magnetization decreases with the increasing interparticle distance.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874159,11074227 and 11204283Zhejiang Provincial Natural Science Foundation(No R6110362)Zhejiang Provincial Innovation Team Project(No 2010R50016).
文摘We report on an order-reversed quenching phenomenon in manganese nitrides under flash melting,which prevents the thermodynamically favorable phase transformations from occurring at high temperatures by providing a narrow window of time.The Mn-N kept un-decomposed at high temperatures generated by current up to 339 MA/m^(2) within 60 ms.After flash melting,the Mn-N shows a significantly enhanced coercivity and a decreased crystalline size.The Mn-N samples decompose rapidly at temperatures above 1100 K with time.The order-reversed quenching technique is potentially useful in processing and preventing phase transformations of meta-stable materials at high temperatures.
文摘Two kinds of Nd 1+ x Ba 2- x Cu 3O 7- δ , the sintered samples and zone melted samples, were treated in pure Ar at 950 ℃. The substitution of Nd ions for Ba ions in the Nd 1+ x Ba 2- x Cu 3O 7- δ before and after the heat treatment was investigated by XRD. In order to know the effects of heat treatment, the T c and J c of samples with and without the heat treatment in Ar were comparatively studied. The results show that the substitution of Nd for Ba decreases, whereas T c and J c increase after the treatment. The Nd 1+ x Ba 2- x Cu 3O 7- δ samples were oxygenated in pure oxygen at 300 ℃ . Based on the XRD spectra it was found that the samples with x <0.4 can transform from tetragonal phase into orthorhombic phase after the oxygenation, whereas in the sample with x >0.4 no phase transition occurs even after a long time oxygenation.
