In order to prepare the bulk samples with high residual magnetization of magnetic compounds, such as (Sm, La)2(Co,Cu,Fe,Zr)17, (Sm,La)1(Co,Cu, Fe)5, Nd2Fe14B, and Pr2Fe14B, directly prepared by solidification, or hot-...In order to prepare the bulk samples with high residual magnetization of magnetic compounds, such as (Sm, La)2(Co,Cu,Fe,Zr)17, (Sm,La)1(Co,Cu, Fe)5, Nd2Fe14B, and Pr2Fe14B, directly prepared by solidification, or hot-deformation , it is the first thing to explore the possibilities of the easy magnetization axis of the whole bulk samples to be arranged in one designed direction. a is defined as the angle between the axis and the direction. In Sm-La-Co-Fe-Cu-Zr system, whetherαis equal to 0°or 90°depends upon not only alloy compositions but also the ratio of the temperature gradient at the solid/liquid interface and the crystal growth rate. To some alloys, a can be changed from 90°to 0°if the ratio is increased to be higher than a critical value, so the c-axis texture orientation can be obtained. In Nd-Fe-B system, the easy magnetization axis of Nd2Fe14B is always perpendicular to the preferential growth direction [ 100], and the easy magnetization axes of Nd2Fe14B grains are randomly distributed in the plane normal to the growth direction even if the growth rate is decreased from 250 to 12μm·-1. But if the magnetization axis of the anisotropic magnet substrate is perpendicular to the heat flux direction of the laser melting solidification layer, c-axis texture of the columnar Nd2Fe14B grains in the layer can be obtained, which is the same as that of the substrate, if the laser scanning rate is not less than 25μm·s-2. Also the c-axis texture [006] can be achieved through hot-deformation of PrxFe93.5-xB5Cu1.5(x = 15 - 19) under the conditions of hot-pressing temperature 973 ~ 1273 K, strain rate 10-3 S-1, and strain 50% ~ 80% .展开更多
During the process of directional solidification,laser remelting/solidification in the layer on sintered magnets, die-upsetting of cast magnets,or die-upsetting of nano-composites,the arrangements of the easy-magnetiz...During the process of directional solidification,laser remelting/solidification in the layer on sintered magnets, die-upsetting of cast magnets,or die-upsetting of nano-composites,the arrangements of the easy-magnetization-axes of the hard magnetic phases(Nd2Fe14B,SmCo5 or Sm2Co17 type)in their designed directions have been studied.In Fe-Pt nano-composite magnets,attempts have been taken to promote phase transformation from disordered,soft magnetic A1 to ordered,hard magnetic L10 FePt phase at reduced temperatures.The dependence of the magnetization and reversal magnetization processes on the microstructures,involving the morphology and three critical sizes of particles of the FePt nano-composite magnets,are summarized. With the decrease of the nominal thickness of the anisotropic FePt film epitaxially grown on the single crystal MgO(001)substrate, the reversal magnetization process firstly changes from full domain wall displacement to partial magnetic wall pinning related to the morphology change,where the coercive force increases abruptly.The reversal magnetization process secondly changes from magnetic wall pinning to incoherent magnetization rotation associated with the particles being below the first critical size at which multi-domain particles turn into single domain ones,where the coercive force is still increased.And the reversal magnetization mode thirdly changes from incoherent to coherent rotation referred to the second critical size,where the increase of the coercive force keeps on.However,when the particle size decreases to approach the third critical size where the particles turn into the supperparamagnetic state,the coercive force begins to decrease due to the interplay of the size effect and the incomplete ordering induced by the size effect.Meanwhile,due to the size effect,Curie temperature of the ultra-small FePt particles reduces.展开更多
基金Project supported by Ministry of Science and Technology (2004CCA04000)Zhejiang Provincial Natural Science Fund of China (M503096)
文摘In order to prepare the bulk samples with high residual magnetization of magnetic compounds, such as (Sm, La)2(Co,Cu,Fe,Zr)17, (Sm,La)1(Co,Cu, Fe)5, Nd2Fe14B, and Pr2Fe14B, directly prepared by solidification, or hot-deformation , it is the first thing to explore the possibilities of the easy magnetization axis of the whole bulk samples to be arranged in one designed direction. a is defined as the angle between the axis and the direction. In Sm-La-Co-Fe-Cu-Zr system, whetherαis equal to 0°or 90°depends upon not only alloy compositions but also the ratio of the temperature gradient at the solid/liquid interface and the crystal growth rate. To some alloys, a can be changed from 90°to 0°if the ratio is increased to be higher than a critical value, so the c-axis texture orientation can be obtained. In Nd-Fe-B system, the easy magnetization axis of Nd2Fe14B is always perpendicular to the preferential growth direction [ 100], and the easy magnetization axes of Nd2Fe14B grains are randomly distributed in the plane normal to the growth direction even if the growth rate is decreased from 250 to 12μm·-1. But if the magnetization axis of the anisotropic magnet substrate is perpendicular to the heat flux direction of the laser melting solidification layer, c-axis texture of the columnar Nd2Fe14B grains in the layer can be obtained, which is the same as that of the substrate, if the laser scanning rate is not less than 25μm·s-2. Also the c-axis texture [006] can be achieved through hot-deformation of PrxFe93.5-xB5Cu1.5(x = 15 - 19) under the conditions of hot-pressing temperature 973 ~ 1273 K, strain rate 10-3 S-1, and strain 50% ~ 80% .
基金Project(2004CCA04000)supported by the National Basic Research Program of ChinaProject(50744014)supported by the National Natural Science Foundation of China+3 种基金Project(2008C21046)supported by Science and Technology Department of Zhejiang Province,ChinaProject(Y406389)supported by Zhejiang Provincial Natural Science Foundation of ChinaProject(2006B100054)supported by Ningbo Bureau of Science and Technology,ChinaProject supported by K.C.Wong Magna Found in Ningbo University,China
文摘During the process of directional solidification,laser remelting/solidification in the layer on sintered magnets, die-upsetting of cast magnets,or die-upsetting of nano-composites,the arrangements of the easy-magnetization-axes of the hard magnetic phases(Nd2Fe14B,SmCo5 or Sm2Co17 type)in their designed directions have been studied.In Fe-Pt nano-composite magnets,attempts have been taken to promote phase transformation from disordered,soft magnetic A1 to ordered,hard magnetic L10 FePt phase at reduced temperatures.The dependence of the magnetization and reversal magnetization processes on the microstructures,involving the morphology and three critical sizes of particles of the FePt nano-composite magnets,are summarized. With the decrease of the nominal thickness of the anisotropic FePt film epitaxially grown on the single crystal MgO(001)substrate, the reversal magnetization process firstly changes from full domain wall displacement to partial magnetic wall pinning related to the morphology change,where the coercive force increases abruptly.The reversal magnetization process secondly changes from magnetic wall pinning to incoherent magnetization rotation associated with the particles being below the first critical size at which multi-domain particles turn into single domain ones,where the coercive force is still increased.And the reversal magnetization mode thirdly changes from incoherent to coherent rotation referred to the second critical size,where the increase of the coercive force keeps on.However,when the particle size decreases to approach the third critical size where the particles turn into the supperparamagnetic state,the coercive force begins to decrease due to the interplay of the size effect and the incomplete ordering induced by the size effect.Meanwhile,due to the size effect,Curie temperature of the ultra-small FePt particles reduces.
