On the formation of the nanostructure in Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo) alloys

The dependence of the formation of the nanocrystalline bcc-Fe phase on the alloy composition is studied for Fe₈₀M₇B₁₂Cu₁ (M: Ti, Ta, Nb, Mo) alloys. The rf-Mössbauer technique is used to determine the optimal soft magnetic properties. This technique allowed us to compare anisotropy fields in each phase present in the composite alloys. The smallest anisotropy field was found in the bcc-Fe nanograins formed in Nb- and Mo-containing alloys.     

Influence of structure on coercivity in nanocrystalline (Fe1−xCox)86Hf7B6Cu1 alloys

The relationship between coercivity and structure in nanocrystalline (Fe_1−xCo_x)₈₆Hf₇B₆Cu₁ (x=0–1) alloys was surveyed. It was found that the increase of Co content in the alloys studied was accompanied by the increase of coercivity. However, we suggest that the factors influencing the coercivity change with the concentration of cobalt in these nanocrystalline alloys. In the iron-rich alloys, the average grain size and magnetostriction play predominant roles in the coercivity. On the other hand, in the case of cobalt-rich alloys, the coercivity mostly originates from the FCC-Co phase with large magnetocrystalline anisotropy and the weak exchange coupling between BCC-Fe(Co) and FCC-Co(Fe).     

Magnetism and hyperfine interactions in EuM2Ge2 and GdM2Ge2(M = Mn,Fe, Co,Ni, Cu)

X-ray, magnetic susceptibility and ¹⁵¹Eu, ¹⁵⁵Gd Mössbauer effect studies of EuM₂Ge₂ and GdM₂Ge₂ were performed. All compounds crystallize in the ThCr₂Si₂ body centered tetragonal structure. In all compounds, except those with M = Mn and in EuM₂Ge₂, the M component carries no magnetic moment. All compounds except those with Mn are antiferromagnetic at low temperatures. In EuMn₂Ge₂ the Mn moments order ferromagnetically at 330 K and change to antiferromagnetic order when the Eu moments order ferromagnetically (9 K). This behaviour is different from that in GdMn₂Ge₂, where the Mn sublattice orders antiferromagnetically at 365 K and becomes ferromagnetic and antiparallel to the ferromagnetic Gd sublattice at 96 K. The Mössbauer studies of ¹⁵¹Eu and ¹⁵¹Gd provide values for the magnetic hyperfine fields, the quadrupole interactions and the orientation of the magnetic moments relative to the local fourfold axis (c-axis). It turns out that in the Eu compounds the easy axis of magnetization is close to the c-axis, while in the Gd compounds it is in the basal plane. In all systems, excluding those with Mn, the interatomic rare earth-rare earth distances have the dominant effect on the conduction electron charge density and polarization at the rare earth site and on the Curie point.     

Soft magnetic properties of amorphous Fe52Co34Hf7B6Cu1 alloy treated by pulsed magnetic field and annealing

<正>The crystallization,microstructure,and soft magnetic properties of Fe₅₂Co₃₄Hf₇B₆Cu₁ alloy are studied.Amorphous Fe₅₂Co₃₄Hf₇B₆Cu₁ alloys are first treated by a pulsed magnetic field with a medium frequency,and then annealed at 100℃-400℃for 30 min in a vacuum.The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer.The soft magnetic properties of specimens are measured by a vibrating sample magnetometer（VSM）.The microstructure changes of specimens are observed by a Mossbauer spectroscopy and transmission electron microscope（TEM）.The results show the medium-frequency pulsating magnetic field will promote nanocrystallization of the amorphous alloy with a lower temperature rise.The nanocrystalline phase isα-Fe（Co） with bcc crystal structure,and the grain size is about 10 nm.After vacuum annealing at 100℃for 30 min,scattering nanocrystalline phases become more uniform,the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.     

Ni-X-In(X=Mn,Fe和Co)合金的缺陷稳定性和磁性能的第一性原理研究

Ni-Mn-In是一种新型的磁控形状记忆合金, 它通过磁场诱导逆马氏体相变实现形状记忆效应. 实验中常围绕化学计量比Ni₂MnIn合金进行成分调整, 以获得适宜的马氏体相变温度与居里温度, 在这个过程中必然会产生多种点缺陷. 本文使用量子力学计算软件包VASP, 在密度泛函理论的框架下通过第一原理计算, 系统地研究了非化学计量比Ni-X-In(X=Mn, Fe 和Co)合金的缺陷形成能和磁性能. 反位缺陷中, In和Ni在X亚晶格的反位缺陷(In_X和Ni_X)的形成能最低, Ni和X反位于Y的亚晶格(Ni_Y和X_Y)得到较高的形成能. 因此, In原子可以稳定立方母相的结构, 而X原子对母相结构稳定性的影响则相反; 空位缺陷中最高的形成能出现在In空位缺陷, 再次肯定了In原子对稳定母相结构的作用. 此外, 详细研究了点缺陷周围原子的磁性能以及电荷分布. 本文的计算结果在指导实验中的成分设计和开发新型磁控形状记忆合金方面具有重要意义.     

Fe39.4－xCo40Si9B9Nb2.6Cux纳米晶合金的有效磁各向异性研究

采用多晶材料趋近饱和定律研究了非晶Fe_39.4-xCo₄₀Si₉B₉Nb_2.6Cu_x(x=0.5,1,1.5) 合金在不同温度纳米晶化后的有效磁各向异性常数〈K〉.结果表明， Cu含量较低(x=0.5)时，纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相，〈K〉随退火温度T_a升高显著增加；随着Cu含量的增加，有效地细化了晶粒，并且抑制了硼化物的析出，〈K〉明显减小.讨论了〈K〉与晶粒尺寸D及初始磁导率的关系. 关键词： 纳米晶 有效磁各向异性 磁导率 FeCo基合金     

Mössbauer spectra and magnetic properties of Sm2 (Co,Fe)17 alloys

Hyperfine Interactions - Sm2(Co1?x Fe x )17 alloys form the basis of a new class of permanent magnets. We have investigated these materials with57Fe Mössbauer spectroscopy. Alloys...     

磁场对模板法制备的Co纳米线结构和磁性的影响

在用二次氧化法制备的高度有序的氧化铝模板上通过交流电化学方法制备了Co纳米线阵列．研究了外加磁场及电解液pH值对纳米线生长的影响．在pH值为6.0和6.5的电解液中分别在不加磁场和沿纳米线轴向施加0.3 T磁场情况下制备了hcp结构的Co纳米线阵列．实验数据表明,沉积时外加磁场和调节pH值能有效影响纳米线中hcp结构的Co晶粒的易磁化轴沿纳米线长轴方向生长．由于晶粒的磁晶各向异性和纳米线沿长度方向的宏观形状各向异性叠加,制备的Co纳米线阵列具有高垂直各向异性,高矫顽力和较高矩形比． 关键词： Co纳米线阵列 织构 磁性     

Spin wave relaxation and magnetic properties in [M/Cu] super-lattices; M=Fe, Co and Ni

In this work, we study the elementary excitations and magnetic properties of the [M/Cu] super-lattices with: M=Fe, Co and Ni, represented by a Heisenberg ferromagnetic system with N atomic planes. The nearest neighbour (NN), next nearest neighbour (NNN) exchange, dipolar interactions and surface anisotropy effects are taken into account and the Hamiltonian is studied in the framework of the linear spin wave theory. In the presence of the exchange alone, the excitation spectrum E(k) and the magnetization 〈S^z〉/S analytical expressions are obtained using the Green's function formalism. The obtained relaxation time of the magnon populations is nearly the same in the Fe and Co-based super-lattices, while these magnetic excitations would last much longer in the Ni-based super lattice. A numerical study of the surface anisotropy and long-ranged dipolar interaction combined effects are also reported. The exchange integral values deduced from a comparison with experience for the three super-lattices are coherent.     

Ga2基Heusler合金Ga2XCr(X = Mn,Fe, Co,Ni, Cu)的四方畸变、电子结构、磁性及声子谱的第一性原理计算

运用基于密度泛函理论的第一性原理的方法, 对Ga₂基Heusler合金Ga₂XCr (X = Mn, Fe, Co, Ni, Cu)的四方畸变、电子结构、磁性及声子谱特性进行了系统的研究. 结果表明, 在保持体积不变的四方畸变中, 五种合金的磁矩主要由Cr元素提供; Ga₂FeCr, Ga₂CoCr和Ga₂CuCr保持稳定的立方相, 而在Ga₂MnCr和Ga₂NiCr 中观察到能量更低的四方相, 且其能量最低点对应的c/a分别位于1.28和1.11处, 而对应的能量差ΔE 分别为-8.26 meV和-6.14 meV. 电子结构显示, Ga₂MnCr和Ga₂ NiCr的费米能级附近存在尖锐的电子态密度峰, 导致3d电子能级杂化向宽能量范围扩展, 以消除体系的高能量不稳态, 这个过程导致结构转变的发生. 基于适度的畸变度和能量差, 本文认为Ga₂MnCr有存在铁磁马氏体相变的可能, 其声学支虚频的出现, 也进一步表明体系有声子模软化的行为.     

稀土含量对速凝工艺制备(Nd,Dy)-(Fe,Al)-B合金结构和磁性能的影响

采用双合金法制备了不同稀土含量的(Nd,Dy)-(Fe,Al)-B合金系列,研究了稀土含量的多寡对薄带和最终烧结磁体的微观结构和磁性能的影响.研究结果表明,适量的稀土含量(～3145%)不仅能改善速凝带主相(Nd,Dy)₂Fe₁₄B的单相性,还有利于富稀土(Nd,Dy)相在晶界的均匀分布.当主相薄带的稀土含量在接近2∶14∶1相稀土含量时,磁体的内禀矫顽力和磁能积显著提高.当稀土含量较少时,对速凝薄带的合适时效热处理将能有效地提高最终烧结NdFeB磁体的磁特性. 关键词： 双相烧结 速凝技术 微观结构 磁性能     

Mössbauer and magnetic studies of nanosize (Fe,Co) x C1 − x alloys

We report on preliminary results from a systematic study of the hyperfine (HF) structure of antiprotonic helium. This precise measurement which was commenced in 2006, has now been completed. Our initial analysis shows no apparent density or power dependence and therefore the results can be averaged. The statistical error of the individual lines is a factor of 60 smaller than that of three body quantum electrodynamic (QED) calculations, while the difference has been resolved to a precision comparable to theory (a factor of 10 better than our first measurement). Agreement between theory and experiment would lead to an increased precision of the measurement for the antiproton magnetic moment and provide a test of CPT invariance.