Uniaxial pressure dependencies of the electric properties of perovskite-like La_(0.85)Sr_(0.15)MnO_(3)(0.2≤x≤0.6)system have been investigated.A large nonlinear piezoresistance effect and a remarkable pressure-induc...Uniaxial pressure dependencies of the electric properties of perovskite-like La_(0.85)Sr_(0.15)MnO_(3)(0.2≤x≤0.6)system have been investigated.A large nonlinear piezoresistance effect and a remarkable pressure-induced change of metal-semiconductor(M-S)transition have been observed.For La_(0.85)Sr_(0.15)MnO_(3),the piezoresistance value can reach about 86%at 290K under a pressure of 16.8MPa,and the pressure coefficient of Tp,the onset of the M-S transition,is as high as 6.4 K/MPa,which is significantly larger than that of known similar pressure effects.These pressure effects suggest that the resistivity of the perovskite compounds is relative not only to double exchange but also to the symmetry of lattice.This phenomenon may provide another route in understanding the colossal magnetoresistance behavior in the perovskites.展开更多
TheHall Effect of(Co_(0.34)Fe_(0.66))_(0.42)(SiO_(2))_(0.58)Granular Films(volume fraction)granular films were fabricated by using magnetron sputtering technique,and a saturated Hall resistivity ρ_(xys) of about 29μ...TheHall Effect of(Co_(0.34)Fe_(0.66))_(0.42)(SiO_(2))_(0.58)Granular Films(volume fraction)granular films were fabricated by using magnetron sputtering technique,and a saturated Hall resistivity ρ_(xys) of about 29μΩ.cm was observed at room temperature,which was almost 3 orders of magnitude greater than that in the pure ferromagnetic sample.The measured linear dependence of resistivity ρ_(xx) vs log_(10)T and magnetoresistance effect indicated that the Co_(0.34)Fe_(0.66) volume fraction in the films were near percolation threshold.The giant Hall effect inHall Effect of(Co_(0.34)Fe_(0.66))_(0.42)(SiO_(2))_(0.58)Granular Films granular film may originate from percolation phenomenon.展开更多
The magnetic properties and magnetoresistance of Pr_(0.7)Pb_(0.3)MnO_(3) single crystals have been studied.At low temperature,the temperature dependence of magnetization can be represented as M(T)=M(0)(1-BT^(3/2)).A l...The magnetic properties and magnetoresistance of Pr_(0.7)Pb_(0.3)MnO_(3) single crystals have been studied.At low temperature,the temperature dependence of magnetization can be represented as M(T)=M(0)(1-BT^(3/2)).A large B value was observed.The spontaneous magnetic moment is slightly larger than the spin-only value for Mn3+and Mn4+ions.Above the Curie temperature,the susceptibility obeys the Curie-Weiss Law and the resistivity R can fit well with R0 exp(T0/T)^(1/4).It is found that the effective paramagnetic moment obtained from the Curie constant is larger than the theoretical value.The large effective paramagnetic moment may originate from the magnetic clusters.A large low-field magnetoresistance of ΔR/R(0)=-50% is observed at 230 K in 1T.展开更多
A large magnetic entropy change about twice as high as that of pure gadolinium metal near room temperature has been discovered in manganese perovskites La_(0.837)Ca_(0.098)Na_(0.038)Mn_(0.987)O_(3.00)(8.3 J·kg^(-...A large magnetic entropy change about twice as high as that of pure gadolinium metal near room temperature has been discovered in manganese perovskites La_(0.837)Ca_(0.098)Na_(0.038)Mn_(0.987)O_(3.00)(8.3 J·kg^(-1)·K^(-1),at 256K)and La_(0.822)Ca_(0.096)K_(0.043)Mn_(0.974)O_(3.00)(6.8 J·kg^(-1)·K^(-1),at 265 K)under a magnetic field of 1.5 T.This phenomenon indicates that manganese perovskites have potential applications for magnetic refrigerants in an extended temperature range even near room temperature.展开更多
A series of Fe_(45.51)(Al_(2)0_(3))_(54.49)nano-granular films were prepared using ion-b€am sputtering technique.A saturated h^ll resistivity of about 12.5μΩ·cm at room temperature was observed.The trstnsmissio...A series of Fe_(45.51)(Al_(2)0_(3))_(54.49)nano-granular films were prepared using ion-b€am sputtering technique.A saturated h^ll resistivity of about 12.5μΩ·cm at room temperature was observed.The trstnsmission electron microscopy image showed that very small Fe particles of smaller than Inm are embedded in Al_(2)0_(3)matrix,and connected into network.The measured p-T curve indicated that this giant Hall effect may originate from the percolation phenomenon.With different annealing temperature(TA)up to 300℃,the saturated Hall resistivity decreased only a little.The good thermal stability of Fe_(45.51)(Al_(2)0_(3))_(54.49)nano-granular Films showed potential application for magnetic sensor.展开更多
(La_(0.67)Tb_(0.33))_(2/3)Sr_(1/3)MnO_(3) has been studied in order to probe mechanisms responsible for the giant magnetore-sistonce ratios and the lattice effect in this kind of compound.The experiment has shown a st...(La_(0.67)Tb_(0.33))_(2/3)Sr_(1/3)MnO_(3) has been studied in order to probe mechanisms responsible for the giant magnetore-sistonce ratios and the lattice effect in this kind of compound.The experiment has shown a strong connection between the magnetotransport and magnetovolume properties.An applied magnetic Geld not only gives rise to a large negative magnetoresistance(-900%)but also produces two different magnetovolume effects which reflect two different magnetostriction mechanisms in the compound.展开更多
New modified Fe3O4-Ba(or Sr)Fe_(12)O_(19)nanoparticles were prepared by using an epitaxial technique for high density magnetic recording.Coercive force reduced from 6.5kOe of M-type ferrite particles to minimal about ...New modified Fe3O4-Ba(or Sr)Fe_(12)O_(19)nanoparticles were prepared by using an epitaxial technique for high density magnetic recording.Coercive force reduced from 6.5kOe of M-type ferrite particles to minimal about 0.2kOe of modified particles,and saturation magnetization increased from 62.2 to 82.6emu/g at the same time.These parameters,Hcσs,and particle size d,can be easily controlled by changing the content of coating material.The magnetic measurements have shown that the modified particles have an interface coupling between epitaxial layer and core particle.As a result of x-ray diffraction measurements,the reflection intensity of spinel phase increases and that of hexagonal magnetoplumbite phase decreases with the increasing number of Fe^(2+)ions.The shape of modified particles gradually changes from hexagonal platelike of M-type ferrite particles to square platelike of modified particles.The analysis shows that the Fe^(2+)ions in suspension directly combined with Fe^(3+)ions from R-block of core particle to form Fe_(3)O_(4)layer.展开更多
Perovskitelike manganese oxides La_(l-x)Na_(x)MnO_(z)(x=0.075,0.100,0.165,0.200)have been fabricated using sol-gel technique.Structure analysis,temperature programmed reduction(TPR)technique and magnetic measurement h...Perovskitelike manganese oxides La_(l-x)Na_(x)MnO_(z)(x=0.075,0.100,0.165,0.200)have been fabricated using sol-gel technique.Structure analysis,temperature programmed reduction(TPR)technique and magnetic measurement have been used to study the effect of Na ion substituted amount on Mn-O distance,the oxygen content,and the magnetocaloric properties of these materials.Results show there is no clear correlation between the substituted amount and mean Mn valence,but a close relationship is observed between Tc and the bond distance of Mn-O.These materials have quite large magnetic entropy changes upon an application of a low magnetic field and can be utilized as more suitable candidates for magnetic refrigerants with wide temperature span.展开更多
A series of Co-Ag granular films were deposited onto a glass substrate with a thickness on the order of 400nm using the ion-beam cosputtering technique.Granular films ranging in composition from about 0-100%fraction b...A series of Co-Ag granular films were deposited onto a glass substrate with a thickness on the order of 400nm using the ion-beam cosputtering technique.Granular films ranging in composition from about 0-100%fraction by volume of cobalt have been prepared.Polar Kerr rotation spectra of the films were measured at room temperature in the wavelength region between 400 and 850nm.A maximum Kerr rotation angle(θk)of 0.28ºwas obtained when a magnetic field of 10kOe was applied perpendicular to the film plane.Our results indicate that the Co particle density and the microstructure between the Co particles and Ag matrix may play an important role in the Kerr rotation.展开更多
Magnetic entropy change larger than that of gadolinium has been observed in perovskite manganese oxides La_(0.67-x)Gd_(x)Ca_(0.33)MnO_(3)(x=0,0.1,0.15)with fixed carrier concentration.The large magnetic entropy change...Magnetic entropy change larger than that of gadolinium has been observed in perovskite manganese oxides La_(0.67-x)Gd_(x)Ca_(0.33)MnO_(3)(x=0,0.1,0.15)with fixed carrier concentration.The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the anomalous thermal expansion just at the Curie temperature.This phenomenon indicates potential applications for magnetic refrigerants in an extended high temperature range.展开更多
Raman scattering from Zn fine spheric particles coated with ZnO of variable thickness is measured, and a broad line can be found. The Raman line shifts to lower frequency side with the increase of oxide thickness. A t...Raman scattering from Zn fine spheric particles coated with ZnO of variable thickness is measured, and a broad line can be found. The Raman line shifts to lower frequency side with the increase of oxide thickness. A theoretical analysis based on the existence of surface phonon mode has been made. Agreement between experiment and theory is good.展开更多
An improved sputtering method,which is named "in situ oxidizing sputtering",was used to prepare periodic Ni/NiO multilayers.Samples studied in this letter contains 20 pairs of Ni/NiO with period about 100 A....An improved sputtering method,which is named "in situ oxidizing sputtering",was used to prepare periodic Ni/NiO multilayers.Samples studied in this letter contains 20 pairs of Ni/NiO with period about 100 A.In Raman scattering,the low frequency phonon modes are hiterpreted as LA phonon folding effect,which is usually measured in superlattices with a strict periodic structure.The ferromagnetic resonance spectra were also recorded at room temperature with microwave frequency 9.777 GHz.The analysis of spin wave resonance indicates that Ni sublayers are coupled with each other,which is the mechanism that surely relates to the amorphous-like NiO spacers.展开更多
The electric and magnetic properties in granular perovskite La_(0.8)Sr_(0.2)MnO_(3) have been investigated.A giant magnetoresistance(GMR)has been observed at temperatures well below TC,the Curie temperature,associated...The electric and magnetic properties in granular perovskite La_(0.8)Sr_(0.2)MnO_(3) have been investigated.A giant magnetoresistance(GMR)has been observed at temperatures well below TC,the Curie temperature,associated with crystal intrinsic magnetic properties.The granular GMR effect is also isotropic but shows some characteristics different from those in the films and crystals of similar perovskites.This suggests an effect of interfacial spin-dependent tunneling in the granular perovskite at temperatures much lower than T_(C).In addition,with the reduction of grain size,an evident superparamagnetic behavior has been observed.展开更多
基金Supported by the 85' Climbing Program,No.6 Nano-material Science,PRC.
文摘Uniaxial pressure dependencies of the electric properties of perovskite-like La_(0.85)Sr_(0.15)MnO_(3)(0.2≤x≤0.6)system have been investigated.A large nonlinear piezoresistance effect and a remarkable pressure-induced change of metal-semiconductor(M-S)transition have been observed.For La_(0.85)Sr_(0.15)MnO_(3),the piezoresistance value can reach about 86%at 290K under a pressure of 16.8MPa,and the pressure coefficient of Tp,the onset of the M-S transition,is as high as 6.4 K/MPa,which is significantly larger than that of known similar pressure effects.These pressure effects suggest that the resistivity of the perovskite compounds is relative not only to double exchange but also to the symmetry of lattice.This phenomenon may provide another route in understanding the colossal magnetoresistance behavior in the perovskites.
基金Supported in part by the National Key Project for Basic Research under Grant No.G1999064508the National Natural Science Foundation of China under Grant No.19890310(4).
文摘TheHall Effect of(Co_(0.34)Fe_(0.66))_(0.42)(SiO_(2))_(0.58)Granular Films(volume fraction)granular films were fabricated by using magnetron sputtering technique,and a saturated Hall resistivity ρ_(xys) of about 29μΩ.cm was observed at room temperature,which was almost 3 orders of magnitude greater than that in the pure ferromagnetic sample.The measured linear dependence of resistivity ρ_(xx) vs log_(10)T and magnetoresistance effect indicated that the Co_(0.34)Fe_(0.66) volume fraction in the films were near percolation threshold.The giant Hall effect inHall Effect of(Co_(0.34)Fe_(0.66))_(0.42)(SiO_(2))_(0.58)Granular Films granular film may originate from percolation phenomenon.
基金Supported by the National Natural Science Foundation of China under Grant No.19774032.
文摘The magnetic properties and magnetoresistance of Pr_(0.7)Pb_(0.3)MnO_(3) single crystals have been studied.At low temperature,the temperature dependence of magnetization can be represented as M(T)=M(0)(1-BT^(3/2)).A large B value was observed.The spontaneous magnetic moment is slightly larger than the spin-only value for Mn3+and Mn4+ions.Above the Curie temperature,the susceptibility obeys the Curie-Weiss Law and the resistivity R can fit well with R0 exp(T0/T)^(1/4).It is found that the effective paramagnetic moment obtained from the Curie constant is larger than the theoretical value.The large effective paramagnetic moment may originate from the magnetic clusters.A large low-field magnetoresistance of ΔR/R(0)=-50% is observed at 230 K in 1T.
基金Supported by the National Natural Science Foundation of China under Grant No.50072007the National Kay Project for Basic Research(No.G1999064508)the National Kay Project for Science and Technology(No.99-A30-01-03).
文摘A large magnetic entropy change about twice as high as that of pure gadolinium metal near room temperature has been discovered in manganese perovskites La_(0.837)Ca_(0.098)Na_(0.038)Mn_(0.987)O_(3.00)(8.3 J·kg^(-1)·K^(-1),at 256K)and La_(0.822)Ca_(0.096)K_(0.043)Mn_(0.974)O_(3.00)(6.8 J·kg^(-1)·K^(-1),at 265 K)under a magnetic field of 1.5 T.This phenomenon indicates that manganese perovskites have potential applications for magnetic refrigerants in an extended temperature range even near room temperature.
基金Supported in part by the National Natural Science Foundation of China under Grant No.19890310(4)the Climbing Program of China(NMS-07)Natural Science Foundation of Jiangsu(BK97039).
文摘A series of Fe_(45.51)(Al_(2)0_(3))_(54.49)nano-granular films were prepared using ion-b€am sputtering technique.A saturated h^ll resistivity of about 12.5μΩ·cm at room temperature was observed.The trstnsmission electron microscopy image showed that very small Fe particles of smaller than Inm are embedded in Al_(2)0_(3)matrix,and connected into network.The measured p-T curve indicated that this giant Hall effect may originate from the percolation phenomenon.With different annealing temperature(TA)up to 300℃,the saturated Hall resistivity decreased only a little.The good thermal stability of Fe_(45.51)(Al_(2)0_(3))_(54.49)nano-granular Films showed potential application for magnetic sensor.
基金Supported by the National Natural Science Foundation of China under Grant No.19890310(4).
文摘(La_(0.67)Tb_(0.33))_(2/3)Sr_(1/3)MnO_(3) has been studied in order to probe mechanisms responsible for the giant magnetore-sistonce ratios and the lattice effect in this kind of compound.The experiment has shown a strong connection between the magnetotransport and magnetovolume properties.An applied magnetic Geld not only gives rise to a large negative magnetoresistance(-900%)but also produces two different magnetovolume effects which reflect two different magnetostriction mechanisms in the compound.
基金Supported by the National Natural Science Foundation of China under Grand No.59671021the Climbing Program of the State Science and Technology Commission of China under Grant No.920232003.
文摘New modified Fe3O4-Ba(or Sr)Fe_(12)O_(19)nanoparticles were prepared by using an epitaxial technique for high density magnetic recording.Coercive force reduced from 6.5kOe of M-type ferrite particles to minimal about 0.2kOe of modified particles,and saturation magnetization increased from 62.2 to 82.6emu/g at the same time.These parameters,Hcσs,and particle size d,can be easily controlled by changing the content of coating material.The magnetic measurements have shown that the modified particles have an interface coupling between epitaxial layer and core particle.As a result of x-ray diffraction measurements,the reflection intensity of spinel phase increases and that of hexagonal magnetoplumbite phase decreases with the increasing number of Fe^(2+)ions.The shape of modified particles gradually changes from hexagonal platelike of M-type ferrite particles to square platelike of modified particles.The analysis shows that the Fe^(2+)ions in suspension directly combined with Fe^(3+)ions from R-block of core particle to form Fe_(3)O_(4)layer.
基金Supported by the National Natural Science Foundation of China under Grate No.59676021 and 85-06 Nano-materials Science。
文摘Perovskitelike manganese oxides La_(l-x)Na_(x)MnO_(z)(x=0.075,0.100,0.165,0.200)have been fabricated using sol-gel technique.Structure analysis,temperature programmed reduction(TPR)technique and magnetic measurement have been used to study the effect of Na ion substituted amount on Mn-O distance,the oxygen content,and the magnetocaloric properties of these materials.Results show there is no clear correlation between the substituted amount and mean Mn valence,but a close relationship is observed between Tc and the bond distance of Mn-O.These materials have quite large magnetic entropy changes upon an application of a low magnetic field and can be utilized as more suitable candidates for magnetic refrigerants with wide temperature span.
基金Supported by the Climbing Program(85-6 NMS)from National Commission of Science and Technology of China under Grant No.920232003the National Natural Science Foundation of China under Grant No.59671021。
文摘A series of Co-Ag granular films were deposited onto a glass substrate with a thickness on the order of 400nm using the ion-beam cosputtering technique.Granular films ranging in composition from about 0-100%fraction by volume of cobalt have been prepared.Polar Kerr rotation spectra of the films were measured at room temperature in the wavelength region between 400 and 850nm.A maximum Kerr rotation angle(θk)of 0.28ºwas obtained when a magnetic field of 10kOe was applied perpendicular to the film plane.Our results indicate that the Co particle density and the microstructure between the Co particles and Ag matrix may play an important role in the Kerr rotation.
基金Supported by the State Major Basic Research Project:Nano-materials Science,and the National Natural Science Foundation of China under Grant No.59671021.
文摘Magnetic entropy change larger than that of gadolinium has been observed in perovskite manganese oxides La_(0.67-x)Gd_(x)Ca_(0.33)MnO_(3)(x=0,0.1,0.15)with fixed carrier concentration.The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the anomalous thermal expansion just at the Curie temperature.This phenomenon indicates potential applications for magnetic refrigerants in an extended high temperature range.
基金the State Major Basic Research Project KNano-Materials Science*1(85-6 NMS)the National Natural Science Foundation of Chinathe National Advanced Materials Commit tee of China.
文摘Raman scattering from Zn fine spheric particles coated with ZnO of variable thickness is measured, and a broad line can be found. The Raman line shifts to lower frequency side with the increase of oxide thickness. A theoretical analysis based on the existence of surface phonon mode has been made. Agreement between experiment and theory is good.
基金Supported by the National Natural Science Foundation of Chinathe National Advanced Materials Committee of China。
文摘An improved sputtering method,which is named "in situ oxidizing sputtering",was used to prepare periodic Ni/NiO multilayers.Samples studied in this letter contains 20 pairs of Ni/NiO with period about 100 A.In Raman scattering,the low frequency phonon modes are hiterpreted as LA phonon folding effect,which is usually measured in superlattices with a strict periodic structure.The ferromagnetic resonance spectra were also recorded at room temperature with microwave frequency 9.777 GHz.The analysis of spin wave resonance indicates that Ni sublayers are coupled with each other,which is the mechanism that surely relates to the amorphous-like NiO spacers.
基金Supported by the 85-06 NMS-the '85 Climbing Program,Nano-Materials Science.
文摘The electric and magnetic properties in granular perovskite La_(0.8)Sr_(0.2)MnO_(3) have been investigated.A giant magnetoresistance(GMR)has been observed at temperatures well below TC,the Curie temperature,associated with crystal intrinsic magnetic properties.The granular GMR effect is also isotropic but shows some characteristics different from those in the films and crystals of similar perovskites.This suggests an effect of interfacial spin-dependent tunneling in the granular perovskite at temperatures much lower than T_(C).In addition,with the reduction of grain size,an evident superparamagnetic behavior has been observed.
