Mn70Fe30-xCox (x=0, 2, 4)合金的组织和磁诱发应变

采用真空非自耗电弧炉熔炼, 然后进行固溶处理制备了Mn₇₀Fe_30-xCo_x (x=0,2,4) 试样. 运用X射线衍射分析、显微组织分析、差示扫描量热法 (DSC)、标准电阻应变计法等实验方法, 研究了添加Co 对Mn-Fe合金的磁诱发应变 (magnetic-field-induced strain, MFIS) 性能的影响. 研究表明, Mn₇₀Fe_30-xCo_x (x=0,2,4)试样在室温下为单一的γ相组织. 随着Co含量的增加, Mn₇₀Fe_30-xCo_x (x=0,2,4)试样的磁性转变温度T_N (Neel点) 呈降低的趋势, 但都高于室温, 在室温下呈现反铁磁性; Mn₇₀Fe_30-xCo_x (x=0,2,4) 试样的最大磁诱发应变也呈增加的趋势. Mn₇₀Fe₂₆Co₄试样的MFIS 在1.1 T时达到60 ppm. 关键词： MnFe合金 Co 磁诱发应变     

Fe和Co元素在铁磁性形状记忆合金Mn50Ni25－xFe(Co)xGa25中的作用

为了进一步改善材料的性能和探索新的材料，将Mn₂NiGa合金中的Ni元素分别用Fe和Co替代，制备了Mn₅₀Ni_25-xFe(Co)_xGa₂₅系列合金. 研究了Fe和Co元素对Mn₂NiGa合金的结构、马氏体相变行为、磁性和机械性能等方面的影响. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni_25-xFe(Co)_xGa₂₅')" href="#">Mn₅₀Ni_25-xFe(Co)_xGa₂₅     

Mn42Al50-xFe8+x合金的磁性和磁热效应

研究了Mn₄₂Al_50-xFe_8+x合金的结构、磁性和磁热效应. 通过成分调节, 居里温度T_C在室温附近一宽温区连续可调, 分别为270 K (Mn₄₂Al₄₂Fe₁₆), 341 K (Mn₄₂Al₄₀Fe₁₈)和370 K(Mn₄₂Al₃₈Fe₂₀). 磁化强度在相变温度处发生一陡降, 热磁曲线和等温磁化曲线均未观察到热和磁的滞后, 表明发生一可逆的二级相变. 在各自居里温度附近, 0-5 T的外磁场变化下磁熵变峰值分别为2.48, 2.52和2.40 J·kg^-1·K^-1. Mn_50-xAl_50-yFe_x+y合金的磁熵变峰值虽然与许多优良的磁制冷材料相比并不大, 但是制备该化合物的原材料价格非常低廉, 制备工艺简单, 加工成型也较容易, 化合物本身耐腐蚀性、延展性较好, 且在居里温度附近发生的是可逆的二级相变, 无晶格或结构的变化, 有利于制冷剂的多次循环使用. 关键词： 磁性 磁热效应 二级相变     

Ga含量对Mn2-xNiGa1+x结构和磁性的影响

系统研究了铁磁性形状记忆合金Mn_{2 -x}NiGa_1+x的结构、磁性和有序化转变. 研究表明: 随着Ga含量的增加, Mn_{2 -x}NiGa_1+x的母相结构由Hg₂CuTi 型逐渐转变到Cu₂MnAl型Heusler结构. 母相的晶格常数先增加后降低, 当x=0.3时达到最大值. 0.3 ≤x ≤0.8时, 材料除呈现Heusler结构的主相之外, 还出现了Ni₂In型六角相. 过渡金属中3d电子之间交换相互作用的减弱, 导致Mn_2-xNiGa_1+x主相的居里温度由Mn₂NiGa的590 K逐渐降低至Ga₂MnNi的220 K左右; 当x=0.6–0.8时, Ni₂In型六角相的居里温度与主相的居里温度出现分离. Ga对Mn的替代引起合金中原子间耦合作用的变化, 导致低温下Mn_{2 -x}NiGa_1+x的饱和磁化强度先增加后降低, 即x≤0.4时呈上升趋势, x>0.4时急剧下降. 差热分析结果显示, 随着x从0增加到1, 样品熔化温度逐渐降低, B2相到Heusler相的转变温度先降低后增加.     

非晶态(Fe1-xVx)84B16合金的磁性和电性

用单辊急冷法制备了非晶态(Fe_1-xV_x)₈₄B₁₆(x=0,0.02,0.04,0.06,0.10)合金的薄带,分别用磁天平和四端引线法测量了饱和磁化强度和高温电阻率的温度关系。得到平均每个磁性原子的磁矩随V含量的增加近似线性下降,计算出每个Fe原子和每个V原子的平均磁矩分别为2.08μ_B和-5.08μ_B。居里温度T_c从x=0时的622K下降到x=0.10时的478K。利用自旋波激发公式:σ(T)=σ(0)(1-BT^* 关键词：     

Co掺杂对Mn$lt;sub$gt;3$lt;/sub$gt;Sn$lt;sub$gt;1-$lt;em$gt;x$lt;/em$gt;$lt;/sub$gt;Co$lt;sub$gt;$lt;em$gt;x$lt;/em$gt;$lt;/sub$gt;C$lt;sub$gt;1.1$lt;/sub$gt;化合物的磁性质、熵变以及磁卡效应的影响

利用固态反应法制备了Mn₃Sn_1-xCo_xC_1.1 （x=0.05,0.1,0.2） 系列化合物,研究了Co掺杂对其磁性质、相变、熵变的影响. 随着Co掺杂量的增加,样品的居里温度由283 K先降到212 K （Mn₃Sn_0.9Co_0.1C_1.1） 后又升到332 K （Mn₃Sn_0.2Co_0.8C_1.1）,相变类型由一级相变逐渐转变为二级相变. 增大Co的掺杂量,Mn₃Sn_1-xCo_xC_1.1化合物的熵变峰值逐渐减小,磁熵变温区由9 K展宽到300 K. 当Co掺杂量为0.2时,相对制冷量达到最高,为103 J/kg （磁场强度为1.6 MA/m）. 由于室温附近良好的磁致冷效应,该类材料在磁制冷领域可能具有重要的应用前景. 关键词： 磁性质 相变 磁卡效应 相对制冷量     

Co50Fe50-xSix合金的结构相变和磁性

利用实验测量和理论计算相结合的方法,研究了介于B2结构CoFe低有序合金和L2₁结构Co₂FeSi高有序合金之间的Co₅₀Fe_50-xSi_x合金的结构相变、磁相变、分子磁矩和居里温度.采用考虑Coulomb相互作用的广义梯度近似(GGA+U)方法计算了合金的能带结构.研究发现,合金出现较强的原子有序倾向,表现出较强的共价成相作用.合金的晶格常数、磁矩、居里温度随Si含量的增加而线性地降低,极限成分Co₂FeSi合金的分子磁矩和居里温度分别达到5.92μ_B和777 ℃.原子尺寸效应导致合金晶格发生变化,但并未成为居里温度和分子磁矩变化的主导因素.分子磁矩的变化符合Slater-Pauling原理,但发现原子磁矩的变化并非线性,据此提出了共价成相对磁性影响的观点.采用Stearns理论解释了居里温度的变化趋势,排除了原子间距对居里温度的主导影响作用.能带计算的结果还表明,Co₂FeSi作为半金属材料并非十分完美,可能在实际应用中会出现自旋极化率降低的问题.发现该系列合金的结构相变和磁相变随着成分的变化聚集在窄小的成分和温度范围内. 关键词： 磁性 Heusler合金 结构相变     

3∶29型Gd3(Fe1-xCox)29-yCry化合物的成相与结构

通过X射线衍射分析和磁测量研究了Gd-Fe-Co-Cr四元系中对应于化学式Gd₃(Fe,Co,Cr)₂₉且Gd含量为一定值的截面内富Fe,Co区的相关系,重点探索了高Co含量3∶29型化合物合成的可能性,研究了3∶29型Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的结构与磁性.研究结果表明,获得3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的范围为:y=5,0≤x≤0.7;y=5.5,0.7≤x≤0.8和y=6,0.8≤x≤0.9.基于对Gd₃(Fe_1-xCo_x)_29-yCr_y化合物成相条件的研究,成功地合成了纯Co基Gd₃Co_29-yCr_y化合物,其固溶范围为6.5≤y≤7.3.3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的晶体结构都属于单斜晶系,Nd₃(Fe,Ti)₂₉型结构,空间群为A2m.得到3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的固溶极限即Co含量的极大值与稳定元素Cr含量有关.Co原子的含量越高,所需稳定元素Cr的含量越大.值得注意的是,用Co原子替代Fe原子会导致Gd₃(Fe_1-xCo_x)_29-yCr_y化合物磁晶各向异性的显著改变.当x≥0.4时,化合物的磁晶各向异性从易面型转变为易轴型 关键词： 3(Fe_1-xCo_x)_29-yCr_y化合物')" href="#">Gd₃(Fe_1-xCo_x)_29-yCr_y化合物 相关系和相结构 X射线衍射 磁晶各向异性     

Gd3Al2-xGax合金的磁熵研究

用磁控电弧炉在氩气气氛中熔炼了Gd₃Al_2-xGax(x=0,0.1,0.3,0.5)系列合金.通过X射线粉末衍射和振动样品磁强计研究了样品的结构和磁熵.发现样品都是由Zr₃Al₂相组成的,且GdAlGa系列合金的ΔS_m要比Gd₃Al₂的大,峰值在室温附近,温区较宽,是一种较好的磁致冷材料. 关键词：     

3:29型Gd-Fe-Co-Cr化合物的结构和磁性

制备了Gd₃(Fe_1-xCo_x)₂₅Cr₄(0≤x≤0.6)和Gd₃Fe_29-yCr_y(3.5≤x≤5.0)化合物,通过X射线衍射和磁性测量手段研究了它们的结构和磁性.实验表明这些化合物都属于A_2/m空间群.Cr含量增加导致居里温度下降,饱和磁化强度降低,磁晶各向异性场下降.Co替代Fe导致单胞体积收缩,居里温度升高,5K的饱和磁化强度在x=0.3左右达到极大值,磁晶各向异性在x=0.4附近由易面转变为易轴. 关键词：     

Y(Mn1-xCox)12磁结构的中子衍射分析

在研究Y(Mn_1-xCo_x)₁₂晶体结构的基础上,为了分析这种化合物的磁结构,我们挑选了不同成分的试样,在液氮温度下作了中子衍射测量。实验上测到的磁有序超结构峰可以用YMn₁₂单胞指标化为h十k+l=2n+1。使用各种可能的磁结构模型对数据进行了分析,根据计算强度与观测强度的最佳拟合,得出了Y(Mn_1-xCo_x)₁₂的磁结构随x变化的某些结论。 关键词：     

The effect of transition element doping on the electronic and magnetic properties of La1.4Sr1.6Mn2O7

The effect of transition element (TE=Cr, Fe, Co, Ni, Cu, Zn) doping on the electronic transport and magnetic properties in the bilayer manganite La_1.4Sr_1.6Mn₂O₇ is studied for the same dopant concentration fixed at 2%. Doping does not cause change in structure but different behavior in magnetic and transport properties. Except for Cr, all the other dopings significantly shift the magnetic transition temperature (T_C) to a lower temperature. Associated with such a decrease, the insulator-metal transition temperature (T_IM) decreases and the peak resistivity (ρ_p) at T_IM increases. Cr doping enhances T_C and T_IM as well as decreases ρ_p. Fe doping apparently has a stronger effect than Co and Ni doping. It is also indicated that Cu doping causes an anomalously large increase in ρ_p. These behaviors are compared with those observed in other bilayer manganites such as La_1.2Sr_1.8Mn₂O₇ as well as in La_0.7Ca_0.3Mn_1−xTE_xO₃.     

Magnetic properties and Griffiths singularity in La0.45Sr0.55 Mn1−xCoxO3

The magnetic properties and the Griffiths singularity were investigated in Mn-site doped manganites of La_0.45Sr_0.55Mn_1−xCo_xO₃ (x=0, 0.05, 0.10 and 0.15) in this work. The parent sample La_0.45Sr_0.55MnO₃ undergoes a paramagnetic-ferromagnetic transition at T_C=290 K and a ferromagnetic-antiferromagnetic transition at T_N=191 K. The doping of Co ions enhances the ferromagnetism and suppresses the antiferromagnetism. The enhanced ferromagnetism results from the fact that the Co doping enhances the Mn³⁺-Mn⁴⁺ double-exchange interaction and induces the Co²⁺-Mn⁴⁺ ferromagnetic superexchange interaction. Detailed investigation on the magnetic behavior above T_C exhibits that the Griffiths singularity takes place in this series of Mn-site doped compounds. The correlated disorder induced by the Co ionic doping, together with the phase competition from the ferromagnetic and the antiferromagnetic interactions among Mn ions, is responsible for the Griffiths singularity.     

First-principle calculations of structural,electronic and magnetic investigations of Mn2RuGe1-xSnx quaternary Heusler alloys

First-principles calculations were used to calculate the structural, electronic and half-metallic ferromagnetism of Mn₂RuGe_1-xSn_x (x?=?0, 0.25, 0.50, 0.75, 1) Heusler alloys. The Hg₂CuTi-type structure is found to be energetic more than Cu₂MnAl-type structure for both Mn₂RuGe and Mn₂RuSn compounds. The calculated lattice constants for Mn₂RuGe and Mn₂RuSn are 5.91?Å and 6.17?Å, respectively. The electronic band structures and density of states of Mn₂RuGe show a half metallic character with total magnetic moments, 2 μ_B per formula unit that are in good agreement with Slater-Pauling rule with indirect band gap, 0.31?eV along the direction Γ –X. It is observed that the total magnetic moment per cell increases as Sn concentration increases in the Heusler alloys.     

Magnetism of Cu2(Mn1−xNix)Sn Heusler alloys

New mixed Heusler alloys of the system Cu₂(Mn_1?xNi_x)Sn were prepared with x = 0–1. Magnetic measurements in the ferromagnetic region were undertaken. For manganese, the only atom displaying a magnetic moment in this row of Heusler alloys, 4μ_B was found, deviations were due to the degree of order. Measurements in the paramagnetic region were not possible because of phase transitions on heating leading to polyphase samples. The critical concentration of magnetic ions was estimated to 13 at.% and compared with models given by Duff and Cannella [6]. With the same plot the Curie point for Cu₂MnSn could be determined (630 K).     

四元Heusler合金NiMnFeGa中Fe原子的磁性贡献

用熔炼和甩带的方法制备了组分为Ni₅₀Fe_xMn_25-xGa ₂₅(x=0—25) 的系列样品.x射线衍射实验结果表明，当Fe取代Mn的含量x＜17时，用熔炼和甩带的方法均 能合成高度有序的L2₁结构的Heusler相.而当x＞17时，普通熔炼方法只能得到 低有序度的 γ相，只有采用甩带急冷的方法才能获得高度有序的纯L2₁结构的化合物.根据 交流磁化率 和分子磁矩的测试结果，初步分析了Fe原子对化合物磁性的贡献，认为Fe原子占据了Mn原子 的位置后，具有高于一般含铁合金的原子磁矩，可达2.55—3.55μ_B. 关键词： Heusler合金 50Fe_xMn_25-xGa_{25')" href="#">Ni50FexMn25-xGa25}     

成分和过渡金属对FeZr基非晶态合金晶化温度的影响

本文系统研究了Fe_100-xZr_x,(Fe_1-xZr_x)₈₄B₁₆和Fe_90-xM_xZr₁₀(M=V,Cr,Mn,Co,Ni,Si,B)非晶态合金的晶化温度与成分的关系。主要结果有:用Zr替代Fe使晶化温度明显提高;在FeMZr非晶态合金系列中,晶化温度依M=Mn,Cr,V元素的顺序和M含量x的增大而提高,而依 关键词：     

Co doping effects on structural, electronic and magnetic properties in Mn2VGa

The electronic structure and magnetic properties of Co-doped Heusler alloys (Mn_1−xCo_x)₂ VGa (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied by first-principles calculations. The results show that the lattice constants decrease with increasing Co content except x=1.0. The spin polarization for x=0.5 is only 34%, much lower than the other concentrations. The compounds of x=0.0, 0.25 show nearly half-metallicity because the Fermi level slightly touches the valence bands. And the compounds of x=0.75, 1.0 exhibit the half-metallic character with 100% spin polarization. It is found the local moments of Mn(Co) basically show a linear increasing trend while the moments of V show a linear decreasing trend with increasing doping concentration. However, the local moments for x=0.5 quite depart from the linear trend. The majority-spin component at the Fermi level increases while the minority-spin component at the Fermi level decreases with the substitution of Co atoms for Mn atoms when x≤0.75. For x≥0.75, the majority-spin component remains more or less the same and the gap in the minority DOS increases with Co doping. The majority spin states are shifted to valence bands and the majority spin states around E_F increase due to a leakage of charge from the unoccupied spin-up states to the occupied majority states with increasing Co content.     

Determination of the sites of Fe atoms in Fe-substituted Mn12

In this paper neutron diffraction experiments were performed for Fe-substituted Mn12 in order to determine the sites of Fe atoms. The results of structure refinements for the sample with our accessed highest Fe content showed that all Fe atoms occupied Mn（3） sites in the Mn12 skeleton. The x-ray absorption fine structure experiments as well as multiple scattering simulations gave the same result. Thus we concluded that Fe atoms only occupied Mn（3） sites. This conclusion also means that Fe-substituted Mn12 series only includes the four single-molecule magnets of [Mn12-xFexO12（CH3COO）16（H2O）4]·2CH3COOH·4H2O （x = 1, 2, 3, and 4）, denoted by Mn11Fe1, Mn10Fe2, MngFe3, and Mn8Fe4, respectively.