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New Modified M-type Ferrite Nanoparticles with Spinel Phase Epitaxial Overlayer

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Chinese Physics Letters 1999年第4期16卷 285-287页

作者： FANG Qing-qing ZHONG wei du you-wei Department of Physics Anhui UniversityHefei 230039 Department of Physics National Laboratory of Solid State MicrostructuresNanjing UniversityNanjing 210093

New modified Fe3O4-Ba(or Sr)Fe_(12)O_(19)nanoparticles were prepared by using an epitaxial technique for high density magnetic *** 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 *** parameters,Hcσs,and particle size d,can be easily controlled by changing the content of coating *** magnetic measurements have shown that the modified particles have an interface coupling between epitaxial layer and core *** 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+)*** shape of modified particles gradually changes from hexagonal platelike of M-type ferrite particles to square platelike of modified *** 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.

关键词： ferrite coating hexagonal

Giant Magnetic Entropy Change in Manganese Perovskites near Room Temperature

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Chinese Physics Letters 2001年第8期18卷 1114-1116页

作者： ZHONG wei CHEN wei WANG Jin-Hui du you-wei National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093 Department of Physics Hebei Normal UniversityShijiazhuang 050091

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 *** phenomenon indicates that manganese perovskites have potential applications for magnetic refrigerants in an extended temperature range even near room temperature.

关键词： temperature. manganese magnetic

Giant Magnetoresistance in Granular Perovskite La_(0.8)Sr_(0.2)MnO_(3)

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Chinese Physics Letters 1997年第3期14卷 229-232页

作者： ZHANG Ning DING wei-ping GUO Zai-bin ZHONG wei du Kai-he du you-wei National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093 Key Laboratory of Jiangsu Province for Optic and Electric Techniques Nanjing Normal UniversityNanjing 210024

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 *** granular GMR effect is also isotropic but shows some characteristics different from those in the films and crystals of similar *** 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.

关键词： properties. perovskite

Phonon and Spin Wave Spectra Study on“in situ Oxidizing Sputtered”Ni/NiO Multilayers

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Chinese Physics Letters 1996年第1期13卷 73-76页

作者： WANG Wen-nai JIANG Zheng-sheng CHENG Guang-xu du you-wei National Laboratory of Solid State Microstructures Center for Advanced Studies in Science and Technology of MicrostructuresNanjing UniversityNanjing 210093 Center of Material Analysis Nanjing UniversityNanjing 210093

An improved sputtering method,which is named "in situ oxidizing sputtering",was used to prepare periodic Ni/NiO *** studied in this letter contains 20 pairs of Ni/NiO with period about 100 *** Raman scattering,the low frequency phonon modes are hiterpreted as LA phonon folding effect,which is usually measured in superlattices with a strict periodic *** ferromagnetic resonance spectra were also recorded at room temperature with microwave frequency 9.777 *** 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.

关键词： structure. phonon amorphous

Structure and Magnetocaloric Properties in Perovskitelike La_(1-x)Na_(x)MnO_(z) Powders

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Chinese Physics Letters 1998年第2期15卷 134-136页

作者： CHEN wei ZHONG wei HOU Deng-lu DING wei-ping du you-wei YAN Qi-jie National Laboratory of Solid State Microstructure Nanjing UniversityNanjing 210093 Department of Chemistry Nanjing UniversityNanjing 210093 Department of Physics Hebei Normal UniversityShijiazhuang 050091

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 *** 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 *** 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 *** 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.

关键词： materials technique substituted

Giant Hall Effect of Fe_(45.51)(Al_(2)0_(3))_(54.49)Nano-granular Film

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Chinese Physics Letters 2000年第3期17卷 227-229页

作者： XU Qing-Yu NI Gang SANG Hai du you-wei National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093

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 *** 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 *** measured p-T curve indicated that this giant Hall effect may originate from the percolation *** different annealing temperature(TA)up to 300℃,the saturated Hall resistivity decreased only a *** good thermal stability of Fe_(45.51)(Al_(2)0_(3))_(54.49)nano-granular Films showed potential application for magnetic sensor.

关键词： technique. resistivity saturated

Large Piezoresistance and Pressure-Induced Change in Electric Properties in Perovskite-like La_(0.85)Sr_(0.15)MnO_(3)

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Chinese Physics Letters 1996年第11期13卷 870-873页

作者： ZHANG Ning DING wei-ping GUO Zai-bing XING Ding-yu du you-wei LI Gang ZHENG Yi-xin National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093 Department of Physics Nanjing Normal UniversityNanjing 210024

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 *** 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 *** pressure effects suggest that the resistivity of the perovskite compounds is relative not only to double exchange but also to the symmetry of *** phenomenon may provide another route in understanding the colossal magnetoresistance behavior in the perovskites.

关键词： resistance perovskite

Large Magnetic Entropy Change in Perovskite La_(0.67-x)Gd_(x)Ca_(0.33)MnO_(3)

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Chinese Physics Letters 1997年第10期14卷 786-788页

作者： HUANG He GUO Zai-bing ZHANG Jian-rong du you-wei National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093

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 *** large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the anomalous thermal expansion just at the Curie *** phenomenon indicates potential applications for magnetic refrigerants in an extended high temperature range.

关键词： temperature entropy attributed

Magnetic Properties and Low-Field Magnetoresistance of Pr_(0.7)Pb_(0.3)MnO_(3) Single Crystals

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Chinese Physics Letters 2001年第4期18卷 598-600页

作者： GU Ben-Xi ZHANG Shi-Yuan du you-wei Department of Physics Nanjing UniversityNanjing 210093

The magnetic properties and magnetoresistance of Pr_(0.7)Pb_(0.3)MnO_(3) single crystals have been *** low temperature,the temperature dependence of magnetization can be represented as M(T)=M(0)(1-BT^(3/2)).A large B value was *** spontaneous magnetic moment is slightly larger than the spin-only value for Mn3+and Mn4+*** 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 *** 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.

关键词： resistance magnetic Crystal