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Magnetocaloric and colossal magnetoresistance Effect in Layered Perovskite La_(1.4) Sr_(1.6)Mn_2O_7

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Journal of Materials Science & Technology 2010年第3期26卷 234-236页

作者： Li'an Han Changle Chen School of science Northwestern Polytechnical University Xi'an 710072 China Department of applied physics Xi'an University of Science and Technology Xi'an 710054 China

Magnetocaloric and colossal magnetoresistance effects of the layered perovskite La 1.4 Sr 1.6 Mn 2 O 7 compound have been studied.A broad peak of magnetic entropy change （-△S M） is found above the Curie temperature （T C =120 K）,which can be associated with the existence of two-dimensional short range ferromagnetic ***,the curvilinear shape of-△S M for layered perovskite is quite different from that of the Ln 1-x A x MnO 3 probably arising from magnetocrystalline *** the same time,a wide peak of colossal magnetoresitance effect near T C is found in the layered provskite La 1.4 Sr 1.6 Mn 2 O 7.

关键词： Magnetocaloric effect Layered perovskite colossal magnetoresistance

Irreversible colossal magnetoresistance in La_(0.58)Dy_(0.09)Ca_(0.33)MnO_3

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Journal of Materials Science & Technology 2003年第6期19卷 622-624页

作者： Baoxin HUANG, Yihua LIU, Ruzhen ZHANG, Youyong DAI, Chengjian WANG, Xiaobo YUAN and Liangmo MEIDepartment of Physics and State Key Laboratory of Crystal Materials, Shandong University, Ji’nan 250100, China Lab. of Crystal Mat. Dept. of Phys. Shandong Univ. Ji'nan 250100 China

The representative sample La0.58Dy0.09Ca0.33MnO3 of Dy doped La0.67Ca0.33MnO3 rare-earth manganites was investigated. The most important effect of Dy doping is to introduce the magnetoimpurity and form the spin clusters which induce dramatically large CMR in La0.58Dy0.09Ca0.33MnO3. The fitting results of field-induced resistivity decrease to the Brillouin function indicate that the CMR is caused by the spin dependent hopping between spin clusters. It is the magnetic field that reduces the size of spin clusters and induces a field-induced irreversible CMR behaviour.

关键词： Spin cluster Magnetoimpurity colossal magnetoresistance

Transport-magnetism Correlation and colossal magnetoresistance in Mixed-valent Manganites

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Journal of Wuhan University of Technology(Materials Science) 2005年第2期20卷 49-52页

作者：李建青袁松柳 Department of Physics Wuhan University of Technology Wuhan 430070 China Assoc.Prof Department of Physics Huazhong University of Science and Technology Wuhan 430074 China Prof

A phenomenological model based on phase separation between ferromagnetic metallic and paramagnetic insulating domains was applied to analyze the electrical transport and colossal magnetoresistance for mixed-valent manganites of RE_(2/3)AE_(1/3)MnO_3. The results show that the model can yield results in agreement with experimental observations in these manganites. The present approach provides a simple picture to visualize the reason that the temperature dependence of resistance (with and without applied magnetic fields) in these compounds has the peculiar shape, without invoking any complicated concept.

关键词： manganite perovskites colossal magnetoresistance magnetic transition

Possible Origins for Paramagnetic-ferromagnetic and Insulator-metal Transitions as well as colossal magnetoresistance in Manganites

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Journal of Wuhan University of Technology(Materials Science) 2009年第6期24卷 903-906页

作者：李建青袁松柳 School of Sciences Huazhong University of Science and Technology

Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach.

关键词： percolation colossal magnetoresistance insulator-metal transition

Magnetic and magnetoresistance Properties in (La_(0.67)Ca_(0.33)MnO_3)_x / (ZrO_2 )_(1-x) Composite System

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Journal of Rare Earths 2005年第2期23卷 194-198页

作者：黄宝歆刘宜华张汝贞原晓波王成建郝小鹏 DepartmentofPhysics WeifangCollegeWeifang261061China DepartmentofPhysics WeifangCollegeWeifang261061China／／DepartmentofPhysicsStateKeyLaboratoryofCrystalMaterialsShandongUniversityJinan250100China

La_(0.67)Ca_(0.33)MnO_3)_x /(ZrO_2)_(1-x) (x is the volume fraction ratio) percolated composites were fabricated by combining La_(0.67)Ca_(0.33)MnO_3 (LCMO) powders with ZrO_2 particles, where LCMO powders were prepared by sol-gel process. Low field magnetoresistance ( LFMR ) is greatly enhanced at low temperature when the system is close to the metallic percolation threshold of x=0.4. The magnetoresistance ratio of ( LCMO)_(0.4) /( ZrO_2 )_(0.6) in a 10 mT magnetic field at 77 K is 7.8 %, about 7.12 times larger than that of pure LCMO compound. The enhancement of spin-dependent tunneling of electrons at the interfaces between LCMO and ZrO_2 grains is responsible for the enhanced LFMR. With increasing ZrO_2 addition, Curie temperature T_C decreases firstly and then remains constant at about 220 K when (x<60%), showing limited substitution effect of Zr ions on B sites.

关键词： inorganic non-metallic materials composite system colossal magnetoresistance interfacial tunneling low-field magnetoresistance rare earths

Influence of the substitution of Sm, Gd, and Dy for La in La_(0.7)Sr_(0.3)MnO_3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

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Journal of Rare Earths 2008年第6期26卷 821-826页

作者：宋启祥王桂英严国清毛强王闻琦彭振生 Spin Electronics and Nano-Materials Research Laboratory Suzhou College Structure Research Laboratory University of Science and Technology of China

A series of La0.7-xSmxSr0.3MnO3, La0.7-xGdxSr0.3MnO3, and La0.7-xDyxSr0.3MnO3 （x=0.00, 0.10, 0.20, 0.30） samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance （MR） was studied through measurements of M-T curves and p-T curves. The results showed that： lattice distortion induced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric properties of pcrovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.

关键词： magnetic and electric properties colossal magnetoresistance Curie temperature substitution of magnetic rare earth element for La perovskite manganite rare earths

Spin Dependent Hopping in Ti Doped La_(0.67)Ca_(0.33)MnO_3

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Journal of Rare Earths 2004年第6期22卷 803-807页

作者：黄宝歆刘宜华张汝贞原晓波王成建梅良模 Department of Physics State Key Laboratory of Crystal Materials Shandong University Department of Physics Weifang University Weifang 261061China

A systematic investigation of the magnetic and transport properties of Ti doped La_(0.67)Ca_(0.33)MnO_3 was reported. The Ti substitution for Mn ions results in a reduction in ferromagnetism and conductivity. The metal-insulator transition temperature is close to Curie temperature which decreases from 274 to 82 K as x increases from 0 to 0.17. The most important effect of Ti doping is to introduce spin clusters in the samples due to the distortion of local lattice and the inhomogeneous magnetic structure induced primarily by the random distribution of Mn ions. A maximum magnetoresistance ratio as large as 90% in 1 T at 122 K was obtained for the sample with x=0.055, which is four times larger than that obtained for LCMO sample at 272 K. There is a remarkable field-history dependent MR in the cooling process for the doped samples while such phenomenon disappears in the warming run. The resistivity follows well the variable range hopping behavior in paramagnetic state. Both the size effect and spin dependent hopping of carriers between the spin clusters should be considered in this system.

关键词： ceramic materials colossal magnetoresistance spin cluster rare earths

High Temperature LFMR in Yttrium Doped Perovskite Manganites

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Journal of Rare Earths 2003年第5期21卷 548-551页

作者：盛晓波童林夙林萍华杨石强储成林翟亚 Department of Electronic Engineering Department of Mechanical Engineering Southeast University Laboratory of Solid State Microstructure Nanjing University

Porous ceramic samples of Y doped perovskite manganites were prepared. In these samples, the transition from high temperature paramagnetic insulator to low temperature ferromagnetic metal as well as the low field magnetoresistance (LFMR) effect at the low temperature is similar to that in dense samples. Opposite to that in dense samples, LFMR effect in porous sample is observed at the high temperature close to the peak of MR T curves. The results suggest that the high temperature LFMR effect and the applicable colossal magnetoresistance (CMR) materials could be obtained by controlling the microstructures of this class of perovskite manganites.

关键词： metal materials colossal magnetoresistance low field magnetoresistance perovskite manganites ceramics rare earths

Simulation of Temperature-Dependent Resistivity for Manganite La1/3Ca2/3MnO3

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Chinese Physics Letters 2006年第6期23卷 1551-1553页

作者：曹硕周庆莉关东仪吕惠宾杨国桢 Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 Department of Physics University of Liaoning Shenyang 110036

The resistivity of the heavy-doped La1/3Ca2/3MnO3 （LCMO） is simulated using a random resistor network model, based on a phase separation scenario. The simulated results agree well with the reported experimental data, showing a transition from a charge-disordered （CDO） state embedded with a few ferromagnetic （FM） metallic clusters to a charge-ordered （CO） state, corresponding to the transition from a high-temperature paramagnetic （PM） insulating state to a low-temperature antiferromagnetic （AF） insulating state. Furthermore, we find that the number of AF/CO clusters increases with decreasing temperature, and the clusters start to connect to each other around 250K, which causes percolating in the system. The results further verify that phase separation plays a crucial role in the electrical conductivity of LCMO.

关键词： PHASE-SEPARATION POSITIVE magnetoresistance colossal magnetoresistance MAGNETIC-FIELD THIN-FILMS OXIDE LA0.9SR0.1MNO3/SRNB0.01TI0.99O3 HETEROJUNCTIONS HETEROSTRUCTURE LA1-XTEXMNO3