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Thermal Growth and Nanomagnetism of the Quasi-one Dimensional Iron Oxide

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Journal of Materials Science & Technology 2011年第11期27卷 985-990页

作者： Minglong zhong zhongwu Liu xichun zhong Hongya Yu Dechang Zeng School of Materials Science and Engineering South China University of Technology Guangzhou 510640 China

Quasi-one dimensional iron oxide nanowires with flat needle shape were synthesized on the iron powders by a rather simple catalyst-free thermal oxidation process in ambient atmosphere. The characterization by field emission scanning electron microscopy （FE-SEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, Raman and high-resolution transmission electron microscopy （HRTEM） revealed that these nanos- tructures are single crystalline α-Fe2O3. The various dimensions with 40-170 nm in width and 1-8 μm in length were obtained by tuning the growth temperature from 280 to 480℃. A surface diffusion mechanism was proposed to account for the growth of quasi-one dimensional nanostructure. The typical α-Fe203 nanowires synthesized at 430℃ had a reduced Morin temperature TM of 131 K in comparison with their bulk counterpart. The coercivitis Hc of these nanowires are 321 and 65 Oe at 5 and 300 K, respectively. The temperature of synthesis also has important effects on the magnetic properties of these nanowires.

关键词： Thermal growth One-dimensional nanostructures Iron oxide Magnetic materials

Development of cost-effective nanocrystalline multi-component(Ce,La,Y)-Fe-B permanent magnetic alloys containing no critical rare earth elements of Dy,Tb,Pr and Nd

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Journal of Materials Science & Technology 2021年第17期76卷 215-221页

作者： Xuefeng Liao Jiasheng Zhang Jiayi He Wenbing Fan Hongya Yu xichun zhong zhongwu Liu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China

Here we first report the fully abundant rare earth(RE)-based nanocrystalline multi-component(Ce,La,Y)-Fe-B alloys containing no critical RE elements of Nd,Pr,Dy,and Tb by melt-spinning *** roles of La and Y substitutions for Ce have been fully *** plays a positive role on both thermal stability and room-temperature(RT)magnetic *** enhanced coercivity H_(cj)by partial substitution of La is attributed to the increases of anisotropy field H_A and the formation of continuously distributed grain boundaries resulting from the suppre s sion of CeFe_(2)*** Y substitution is not benefit for H_(cj),both remanent polarization J_r and thermal stability have been effectively improved since Y_(2)Fe_(14)B shows relatively high saturation magnetization M_s and a positive temperature coefficient of HA over a certain temperature *** addition,RE element segregation has been confirmed,La prefers to enter into the grain boundaries than Ce and Y prefers to remain in the 2:14:1 *** on these understanding,a series of melt-spun(Ce,La,Y)-Fe-B alloys have been designed.A relatively good combination of magnetic properties with maximum energy product(BH)_(max)=7.4 MGOe,H_(Cj)=400 kA/m,and J_r=0.63 T has been obtained in[(Ce_(0.8)La_(0.2))_(0.7)Y_(0.3)]_(17)Fe_(78)B_6 alloy,together with high Curie temperature(T_c=488 K)and low temperature coefficients of remanence(α=-0.255%/K)and coercivity(β=-0.246%/K).

关键词： Nanocrystalline(La Ce Y)-Fe-B alloys Permanent magnets RE element segregation Magnetic properties Thermal stability

Superior comprehensive properties of LaFe_(11.8)Si_(1.2)/Ce_(60)Co_(40) magnetocaloric composites

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Journal of Rare Earths 2024年第6期42卷 1073-1086,I0003页

作者： xichun zhong Yuanxin Li Yucai Wu Jiaohong Huang Cuilan Liu Jian Liu zhongwu Liu Minglong zhong Zhenchen zhong R.V.Ramanujan School of Materials Science and Engineering South China University of TechnologyGuangzhou510640China Baotou Research Institute of Rare Earths Baotou014030China Center for Advanced Solidification Technology School of Materials Science and EngineeringShanghai UniversityShanghai200444China Jiangxi KeyLaboratory for Rare Earth Magnetic Materials and Devices&Institute for Rare Earth Magnetic Materials and Devices(IREMMD) Jiangxi University of Science and TechnologyGanzhou341000China School of Materials Science and Engineering Nanyang Technological University639798Singapore Singapore-HUJ Alliance for Research and Enterprise(SHARE) The Smart Grippers for Soft Robotics(SGSR)ProgrammeCampus for Research Excellence and Technological Enterprise(CREATE)138602Singapor

LaFe_(11.8)Si_(1.2)/10 wt%Ce_(60)Co_(40) composites were prepared by spark plasma sintering and subsequent diffusion annealing.A novel core-shell structure is observed with the LaFe11.8Si1.2 particles as the core and the(La,Ce)_(2)(Fe,Co,Si)_(17)(2:17)phase as the *** diffusion annealing time(t_(a))increases,this core-shell structure is replaced by the formation of the(La,Ce)_(1)(Fe,Co,Si)_(13) *** at 1323 K for 12 h results in samples with(-ΔSM)^(max) of 9.30 J/(kg·K)(Δμ0H=2 T),good mechanical properties((σbc)^(max)=402 MPa,ε=4.21%)and thermal conductivity of 8.7 W/(m·K).Thus,bulk composites with excellent comprehensive properties for magnetic refrigeration are obtained in this work.

关键词： LaFe_(11.8)Si_(1.2)/Ce_(60)Co_(40)composites Spark plasma sintering Diffusion annealing Microstructure evolution Magnetocaloric effect Rareearths

Influence of gadolinium and dysprosium substitution on magnetic properties and magnetocaloric effect of Fe78-xRExSi4Nb5B12Cu1 amorphous alloys

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Journal of Rare Earths 2020年第12期38卷 1317-1321页

作者： Lizhong Zhao Huacun Tian xichun zhong zhongwu Liu Jean-Marc Greneche R.V.Ramanujan Institute of Advanced Magnetic Materials Hangzhou Dianzi UniversityHangzhou 310012China School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Guangdong Institute of Special Equipment Inspection and Research Guangzhou 528251China Institut des Molecules et Materiaux du Mans UMR CNRS 6283 Le Mans UniversiteAvenue MessiaenLe MansF-72085France School of Materials Science and Engineering Nanyang Technological University639798Singapore Singapore-HUJ Alliance for Research and Enterprise(SHARE) Nanomaterials for Energy and Energy-Water Nexus(NEW)Campus for Research Excellence and Technological Enterprise(CREATE)Singapore138602Singapore

Amorphous Fe78-xRExSi4 Nb5 B12Cu1(RE=Gd,Dy) ribbons with different RE contents were prepared by melt spinning to investigate the effect of heavy rare earth(Gd,Dy) substitution on the hyperfine structure,magnetic properties and magnetocaloric *** Curie temperature of RE substituted alloys,hyperfine field and magnetic moments of Fe atoms initially increase up to 1 at% RE content and then decrease monotonously for increasing RE content up to 10 at%.The dependence of magnetic entropy change(-△SM) and refrigeration capacity(RC) of the alloys on RE contents displays the same *** RCAREA values of the alloys substituted with 1 at% Gd and Dy are similar to those of recently reported Fe-based metallic glasses with enhanced RC values compared with those of Gd5 Ge1.9Si2 ***-△SM and RC values,negligible coercive force and hysteresis commonly make these Fe78-xREx-Si4 Nb5 B12Cu1 amorphous alloys as low-cost candidates for high-temperature magnetic refrigeration.

关键词： Magnetic properties Magnetocaloric effect Refrigeration capacity Rare earths

Magnetic properties and large magnetocaloric effects in amorphous Gd-Al-Fe alloys for magnetic refrigeration

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Science China(Physics,Mechanics & Astronomy) 2011年第7期54卷 1267-1270页

作者： ZHENG ZhiGang zhong xichun SU KunPeng YU HongYa LIU zhongWu ZENG DeCheng School of Materials Science & Engineering South China University of Technology Guangzhou 510640 China

A series of the amorphous Gd75-55A125-5Fe0-40 alloy ribbons were prepared by melt spinning. The structure, magnetic properties and magnetocaloric effect （MCE） of these alloys were investigated. The prepared samples have shown the characteristics of a second-order phase transition with zero hysteresis loss and the Tc can be tuned by changing the Fe contents. For the different compositions, the magnetic entropy change （-△Sm） for a field change of 0-5 T reached a maximum value of 7.14 J kg 1 K1 in the Gd70A120Fel0 alloy near its Curie temperature （To） of 149 K. The non-linear composition dependence of （- △ Sin） could be caused by the competitions between Fe-Fe, Fe-Gd and Gd-Gd interactions. The refrigeration capacity （RC） values of these al- loys are about 532-780 J/kg under a magnetic field change of 0-5 T. The results indicate that amorphous GdFeA1 alloys can be considered as ideal candidates for a magnetic refrigerant in the temperature range of 104-222 K.

关键词： Gd-Fe-AI amorphous ribbon magnetocaloric effect

Magnetic properties and magnetic entropy changes of MRE_2Co_7 compounds

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Science China(Physics,Mechanics & Astronomy) 2015年第9期58卷 86-89页

作者： zhong xichun LIU zhongWu MIN JiXiong TIAN HuaCun GSCHNEIDNER Jr Karl A PECHARSKY Vitalij K School of Materials Science and Engineering South China University of Technology Ames Laboratory U.S. Department of Energy and Department of Materials Science and Engineering Iowa State University State Key Laboratory of Optoelectronic Materials and Technologies School of Physics and Engineering Sun Yat-sen University

(La0.5Ce0.5)2Co7 and(Ce0.65Pr0.35)2Co7 compounds for magnetic refrigeration were studied by X-ray diffraction, ac susceptibility and isothermal magnetization measurements. X-ray powder diffraction shows that all the compounds have hexagonal Ce2Ni7-type structure. The Curie temperatures(TC) are 258 K and 222 K for(La0.5Ce0.5)2Co7 and(Ce0.65Pr0.35)2Co7 compounds, respectively. High coercivities(HC) of about 1.74 and 6.61 k Oe at 5 K with a smooth demagnetization curves were obtained for the(La0.5Ce0.5)2Co7 and(Ce0.65Pr0.35)2Co7 compounds, respectively. For an applied field change from 0 to 50 k Oe, the maximum(??SM) for(La0.5Ce0.5)2Co7 and(Ce0.65Pr0.35)2Co7 compounds are 0.52 and 0.67 J/(kg K), respectively.

关键词： (La0.5Ce0.5)2Co7 compound (Ce0.65Pr0.35)2Co7 compound magnetic property magnetic entropy change

Structure,magnetic properties and magnetocaloric effects of Fe_(50)Mn_(15-x)Co_xNi_(35) alloys

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Science China(Physics,Mechanics & Astronomy) 2014年第3期57卷 437-441页

作者： zhong xichun TIAN HuaCun TANG PengFei LIU zhongWu ZHENG ZhiGang ZENG DeChang School of Materials Science and Engineering South China University of Technology

FesoMn15-xCoxNi35 （x=0, 1, 3, 5, 7） alloys were prepared by arc melting under purified argon atmosphere. The ingots were homogenized at 930℃ for 90 h followed by water quenching. The crystal structure, magnetic properties and magnetocaloric effects of the alloys were studied by X-ray diffraction （XRD） and MPMS-7-type SQUID. The results show that all samples still maintained a single γ-（Fe, Ni）-type phase structure. With the increase of the content of Co, the Curie temperatures of these alloys increased and exhibited a second-order magnetic transition from ferromagnetic （FM） to paramagnetic （PM） state near Curie temperature. The maximum magnetic entropy change and the relative cooling power of Fe50Mn10CosNi35 alloy was 2.55 J/kg.K and 181 J/kg, respectively, for an external field change of 5 T. Compared with rare earth metal Gd, FesoMnls-xCoxNi35 series of alloys have obvious advantage in resource price; their Curie temperatures can be tuned to near room temperature, maintain a relatively large magnetic entropy change at the same time and they are a type of potential magnetic refrigeration materials near room temperature.

关键词： Fes0Mnl5-xCoxNi35 alloys magnetic refrigeration Curie temperature magnetocaloric effect

Microstructure improvement related coercivity enhancement for sintered NdFeB magnets after optimized additional heat treatment

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Journal of Rare Earths 2018年第4期36卷 379-384页

作者： Qing Zhou Wei Li Yuan Hong Lizhong Zhao xichun zhong Hongya Yu Lili Huang zhongwu Liu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China Guangdong Research Institute of Rare Metals Guangzhou 510651China

The micro structure, especially the Nd-rich phase and the grain boundary, in sintered NdFeB magnets plays an important role in magnetic reversal and coercivity mechanism. To better understand the effects of the microstructure on the coercivity, we investigated the microstructure and properties improvements of a commercial sintered NdFeB magnet after optimized additional heat treatment. The coercivity is enhanced from 1399 to 1560 kA/m. This enhancement has been explained in terms of the evolution of the grain boundary structure, and the formation of continuous thin layers of Nd-rich phase is important for high coercivity. The micromagnetic simulation together with the numerical analysis based on the nucleation model suggest that the reversed magnetic domains nucleate mainly at the interface of multijunctions of Nd_2 Fe_（14）B grains with high stray fields during the demagnetization process. Both improved anisotropy fields at grain boundaries and reduced stray fields at multi-junction Nd-rich phases contribute to the coercivity enhancement. This work has importance in understanding the crucial micro structure parameters and enhancing the obtainable properties for sintered NdFeB magnets.

关键词： Sintered NdFeB magnets Microstructure Coercivity Micromagnetic simulation Heat treatment Rare earths

Magnetic properties and magnetocaloric effects in amorphous and crystalline Gd_(55)Co_(35)Ni_(10) ribbons

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Science China(Physics,Mechanics & Astronomy) 2013年第6期56卷 1096-1099页

作者： zhong xichun TANG PengFei GAO BeiBei MIN JiXiong LIU zhongWu ZHENG ZhiGang ZENG DeChang YU HongYa QIU WanQi School of Materials Science and Engineering South China University of Technology

The magnetic properties and magnetocaloric effects of amorphous and crystalline Gd55Co35Ni10 ribbons are investigated.A main phase with a Ho 12 Co 7-type monoclinic structure(space group P21/c) and a minor phase with a Ho4Co3-type hexagonal structure(space group P63/m) are obtained for crystalline ribbon after *** amorphous ribbons order ferromagnetically and undergo a second-order transition at 192 *** crystalline Gd55Co35Ni10 ribbons,two magnetic phase transitions occur at 158 and 214 K,*** peak value of-△SM under a field change of 0-5 T is 6.5 J/kg K at 192 K for amorphous Gd55Co35Ni10 ribbons.A relatively large magnetic entropy change(～5.0 J/kg K) under a field change of 0-5 T for the crystalline Gd55Co35Ni10 ribbons is obtained in the temperature interval range of 154-214 *** large platform of magnetic entropy change and the negligible thermal/magnetic hysteresis loss mean the crystalline Gd55Co35Ni10 compound can satisfy the requirement of the Ericsson-type refrigerator working in the temperature range from 154K to 214K.

关键词： Gd55Co35Ni10 ribbon magnetocaloric effect magnetic refrigeration