非晶Fe89.7 P10.3合金纳米线阵列的磁性研究

利用电化学沉积方法在阳极氧化铝模板中制备了Fe89.7P10.3非晶合金纳米线阵列.利用x射线衍射仪、透射电子显微镜、振动样品磁强计和穆斯堡尔谱仪研究了样品的结构和磁性,发现纳米线阵列是非晶结构,且拥有垂直磁各向异性和高的矫顽力,Hc=3.04×104A/m.纳米线内部的平均超精细场和平均同质异能移分别为2.15×106 A/m和0.07 mm/s;而纳米线末端的平均超精细场(2.33×106A/m)大于内部的值,平均同质异能移(0.04mm/s)小于内部的值.另外,纳米线内部Fe原子磁矩与线轴的夹角约为16°,而在纳米线末端Fe原子磁矩与线轴的夹角约为28°.这些结果表明,由于形状各向异性,在纳米线中实现了无序非晶合金磁矩的有序排列.     

铁镍合金纳米线阵列的制备与穆斯堡尔谱研究

用交流电化学沉积方法在阳极氧化铝模板中成功地制备了直径约16nm,长度4μm的Fe_1-xNi_x(0关键词： 纳米线阵列 穆斯堡尔谱 铁镍合金     

121Sb穆斯堡尔同质异能移研究

本文从理论上研究¹²¹Sb的穆斯堡尔同质异能移,从能带理论的观点研究固体电子结构,提出压缩原子模型,考虑固体中原子体积的有限性,并在此基础上计算核内电子电荷密度和¹²¹Sb的穆斯堡尔定标常数。 关键词：     

穆斯堡尔谱学研究非晶TM80M20合金的微观结构

在室温下和4.2K下测定了非晶Fe₈₀B_20-xM_x合金(M=P,C)的穆斯堡尔吸收谱。利用分布参数拟合程序得到了超精细内场H_i和同质异能移IS同类金属成份的变化关系。利用这些结果考察了非晶合金的微观结构,比较了两类结构模型:Bernal-Polk模型和微晶模型。对比非晶合金和它们的相应晶相的行为得知,这类非晶合金中不存在微晶近程序,Bernal-Polk模型对描述TM-M类非晶合金的微观结构优于微晶模型。 关键词：     

高矫顽力型FeCrCo合金相变化的穆斯堡尔谱研究

通过穆斯堡尔谱、透射电镜、x射线和磁测量等手段研究了将普通FeCrCo合金中Cr,Co元素含 量提高、并加入Mo,Zr元素后合金矫顽力的变化，发现其值76kA/m比普通值40—52kA/m高50% 以上.对该合金不同热处理阶段的穆斯堡尔谱的测试表明，合金的微观结构与普通FeCrCo合 金有显著的不同.固溶处理后合金单相性好，不产生对磁性起破坏作用的γ相；磁场热处理 过程中，发生原子的重新排布，α₂相开始出现，两相结构基本确定；分级回火 后，调幅 分解进行得更彻底，合金内部完全形成调幅结构，与低矫顽力合金相比，铁磁性的α₁ 相更容易形成. 关键词： 穆斯堡尔谱 调幅分解 磁超精细场 同质异能移     

α-Fe纳米线阵列膜磁各向异性的穆斯堡尔谱研究

在具有纳米级孔洞的多孔氧化铝模板上,用电沉积方法成功地制备出α-Fe纳米线有序阵列组装膜.分别用透射电子显微镜(TEM)、穆斯堡尔谱仪(MS)和振动样品磁强计(VMS)对样品进行了测试分析.TEM和电子衍射的结果显示,阵列中的纳米线均匀有序,彼此独立,由一串α-Fe单晶磁性颗粒构成.VSM测试结果表明,这种纳米阵列结构具有高度垂直磁各向异性.当外磁场垂直磁化时,磁滞回线具有很高矩形比(0.98)和矫顽力(1.76×10⁵A/m).尤其MS的测试结果显示,阵列中的每根纳米线的总磁矩都沿 关键词：     

CoFe2O4纳米颗粒的结构、磁性以及离子迁移

聚乙烯醇(PVA)溶胶凝胶法制备出CoFe₂O₄纳米微粉，用X射线衍射研究了铁氧体纳米颗粒的结构.测量了CoFe₂O₄纳米颗粒80—873 K的变温穆斯堡尔谱，发现纳米颗粒的磁转变温度范围为793—813 K，比块体材料的磁性转变温度要低.CoFe₂O₄纳米颗粒的德拜温度θ_A=674 K，θ_B=243 K，比块体材料要小.CoFe₂O₄纳米颗粒超精细场H_f随温度的变化符合T^3/2+T^5/2定理.当温度较高时，平均同质异能移IS随温度的升高而减小，并呈线性关系. 关键词： 纳米颗粒 磁性 穆斯堡尔谱     

Tb0.3Dy0.7(Fe0.9T0.1)1.95合金的结构、自旋重取向和穆斯堡尔谱

系统研究了室温下Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95(过渡金属元素T=Mn，Fe，Co，B，Al，Ga)合金中ⅢA族金属和过渡金属元素T替代Fe对结构、自旋重取向和穆斯堡尔谱的影响.结果发现，不同金属T替代Fe，Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95，合金具有相同的MgCu₂型立方Laves相结构；Al，Ga替代使Tb_0.3Dy_0.7(Fe_0.9T_0.1)_1.95合金的易磁化方向在{110}面逐渐偏离了立方晶体的主对称轴，即自旋重取向，B，Mn，Co替代未使易磁化轴发生明显转动；Al，Ga元素替代使超精细场H_hf略有下降，B，Mn替代对超精细场H_hf的影响不大，而Co元素替代使超精细场H_hf有较大增加；所有元素替代使同质异能移IS有所增加；B，Al，Ga和Mn替代使四极劈裂Q_s增加，而Co替代使四极劈裂Q_s下降. 关键词： 立方Laves相 自旋重取向 穆斯堡尔谱     

穆斯堡尔谱学研究非晶TM_(80)M_(20)~1)合金的微观结构

在室温下和4.2K下测定了非晶Fe_(80)B_(20-x)M_x合金(M=P,C)的穆斯堡尔吸收谱。利用分布参数拟合程序得到了超精细内场H_i和同质异能移IS同类金属成份的变化关系。利用这些结果考察了非晶合金的微观结构,比较了两类结构模型:Bernal-Polk模型和微晶模型。对比非晶合金和它们的相应晶相的行为得知,这类非晶合金中不存在微晶近程序,Bernal-Polk模型对描述TM-M类非晶合金的微观结构优于微晶模型。     

阎隙碳原子对Er2Fe17Cx化合物结构与磁性的影响

利用快淬手段获得高碳含量的Er₂Fe₁₇C_x单相化合物,系统研究了Er₂Fe₁₇C_x(x=0.0,0.5,1.0,1.5,2.0,2.5,2.8和3.0)的结构、相稳定性及内禀磁性,讨论了间隙碳原子对化合物中原子磁矩、交换作用和各向异性的影响,同时用⁵⁷Fe穆斯堡尔效应分析了化合物中各个铁晶位的超精细场随碳含量的变化。 关键词：     

Synthesis and magnetic properties of Fe100-xMox alloy nanowire arrays

The Fe100-xMox(13≤x≤25) alloy nanowire arrays are synthesized by electrodeposition of Fe 2+ and Mo 2+ with different ionic ratios into the anodic aluminum oxide templates.The crystals of Fe100-xMox alloy nanowires gradually change from polycrystalline phase to amorphous phase with the increase of the Mo content and the nanowires are of amorphous structure when the Mo content reaches 25 at%,which are revealed by the X-ray diffraction and the selected area electron diffraction patterns.As the Mo content increases,the magnetic hysteresis loops of Fe100-xMox alloy nanowires in parallel to the nanowire axis are not rectangular and the slopes of magnetic hysteresis loops increase.Those results indicate that the magnetostatic interactions between nanowires and the magnetocrystalline anisotropy both have significant influences on the magnetization reversal process of the nanowire arrays.     

Fabrication and magnetic properties of ordered Fe60Pb40 nanowire arrays electrodeposited in AAO templates

Ordered ferromagnetic-nonmagnetic heterogeneous Fe₆₀Pb₄₀ nanowire arrays were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) image and selected-area diffraction (SAED) pattern analysis showed that the Fe₆₀Pb₄₀ nanowires are polycrystalline with an average diameter of 22 nm and lengths up to several micrometers. X-ray diffraction (XRD) observations indicated that α-Fe and fcc Pb phase coexist and do not form metastable alloy phase. The as-deposited samples were annealed at 200, 300, 400 and 500 ^°C, respectively. Magnetic measurements showed that nanowires have high magnetic anisotropy with their easy axis parallel to the nanowire arrays, and the coercivity of the samples increased with the annealing temperature up to 400 ^°C and reached a maximum (2650 Oe). The change of magnetic properties associated with the microstructure was discussed.     

Fabrication and magnetic properties of amorphous Co0.71Pt0.29 nanowire arrays

Highly ordered Co_0.71Pt_0.29 alloy nanowire arrays have been fabricated successfully by direct current electro-deposition into the pores of a porous anodic aluminum oxide (AAO) template. SEM and TEM images reveal that the nanowires of array are uniform, well isolated, and parallel to one another. The aspect ratio of nanowires is over 200. XRD and EDS pattern indicates that amorphous Co_0.71Pt_0.29 structure was formed during electro-deposition. In amorphous sample, magnetocrystal anisotropy is very small, therefore, shape anisotropy plays a dominant role which leads to strong perpendicular anisotropy. High coercivity (Hc=1.7 kOe) and squareness (Mr/Ms) around 0.7 were obtained in the samples when the field was applied parallel to the axis of the nanowires. However, when it changed to polycrystalline structure after annealing, due to the competition of magnetocrystal anisotropy and shape anisotropy, the sample did not display perpendicular anisotropy.     

高矫顽力的Co70Cu30合金纳米线阵列的制备及磁性研究

利用直流电化学沉积法, 在多孔阳极氧化铝模板中首次制备出了具有[220]取向的单晶 面心立方结构的CoCu固溶体合金纳米线阵列, 其Co含量高达70%.透射电子显微镜显示纳米线均匀连续, 具有较高的长径比, 约为300. 磁性测量表明所制备的Co₇₀Cu₃₀ 合金纳米线具有超高的矫顽力H_c//=2438 Oe(1 Oe=79.5775 A/m)和较高的矩形比S//=0.76, 远高于以往报道的CoCu合金纳米线的磁性, 分析表明磁性好的主要原因是由于较高Co含量和高形状各向异性. 通过磁性测量和模型计算, 得到Co₇₀Cu₃₀ 合金纳米线阵列在反磁化过程中遵从对称扇型转动的球链模型, 并从结构的角度分析了Co₇₀Cu₃₀合金纳米线阵列的反磁化行为.     

Synthesis and characteristics of Co100−xSnx nanowire arrays

Co_100?xSn_x alloy nanowires were fabricated by electrodeposition of Co²⁺ and Sn²⁺ into anodic aluminum oxide (AAO) templates. X-ray diffraction results indicate that the crystal structures of the nanowires changed from polycrystal to amorphism, and then to polycrystal again with the increase of Sn content in the nanowires. Transmission electron microscopy result shows that the nanowires are about 50 nm in diameter and the aspect ratio is approximately 75. The magnetic response of the arrays was measured using vibrating sample magnetometry at room temperature. The results show that the coercivity and squareness with the magnetic field along the nanowire arrays decrease with the increase of the Sn content. Nanowires exhibit obviously uniaxial magnetic anisotropy, and the easy magnetizing axis is parallel to the nanowires owing to the large shape anisotropy.     

Synthesis and magnetic properties of spinel CoFe2O4 nanowire arrays

Spinel CoFe₂O₄ nanowire arrays were synthesized in nanopores of anodic aluminum oxide (AAO) template using aqueous solution of cobalt and iron nitrates as precursor. The precursor was filled into the nanopores by vacuum impregnation. After heat treatment, it transformed to spinel CoFe₂O₄ nanowires. The structure, morphology and magnetic properties of the sample were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicate that the nanowire arrays are compact. And the individual nanowires have a high aspect ratio, which are about 80 nm in diameter and 10 μm in length. The nanowires are polycrystalline spinel phase. Magnetic measurements indicate that the nanowire arrays are nearly magnetic isotropic. The reason is briefly discussed. Moreover, the temperature dependence of the coercive force of the nanowire arrays was studied.     

Autocatalytic redox fabrication and magnetic studies of Co-Ni-P alloy nanowire arrays

Uniform and large-scale Co-Ni-P alloy nanowire arrays have been fabricated by autocatalytic redox reaction in an anodic alumina membrane (AAM). The images of Co-Ni-P alloy nanowire arrays and single nanowires are obtained by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that the Co-Ni-P nanowire arrays are amorphous in structure. The magnetic property of Co-Ni-P nanowire arrays is characterized using a vibrating sample magnetometer (VSM). The hysteresis loops show that the easily magnetized direction of Co-Ni-P nanowire arrays is parallel to the nanowire arrays and that it has obvious magnetic anisotropy as a result of the shape anisotropy.     

Synthesis and magnetic properties of ordered barium ferrite nanowire arrays in AAO template

BaFe₁₂O₁₉ nanowire arrays having single magnetic domain size (≤460 nm) in anodic aluminum oxide (AAO) templates were prepared by sol-gel and self-propagating high-temperature synthesis techniques. The diameter of the nanowire arrays is approximately 70 nm and the length is about 2-4 μm. The specimens were characterized using X-ray diffraction, vibrating sample magnetometer, field emission scan electron microscope, atomic force microscopy and microwave vector network analyzer. The magnetic properties of BaFe₁₂O₁₉ nanowire arrays embedded in AAO templates were measured by VSM with a field up to 1274 KA/m at room temperature. The results indicate that the nanowire arrays exhibit large saturation magnetization and high coercivity in the range of 6000 Oe and an obvious magnetic anisotropy with the easy magnetizing axis along the length of the nanowire arrays, probably due to the shape anisotropy and magneto-crystalline anisotropy. Finally the microwave absorption properties of the nanowires were discussed.     

Magnetic domain structure in small diameter magnetic nanowire arrays

Fe_0.3Co_0.7 alloy nanowire arrays were prepared by ac electrodepositing Fe²⁺ and Co²⁺ into a porous anodic aluminum oxide (PAO) template with diameter about 50 nm. The surface of the samples were polished by 100 nm diamond particle then chemical polishing to give a very smooth surface (below ±10 nm/μm²). The morphology properties were characterized by SEM and AFM. The bulk magnetic properties and domain structure of nanowire arrays were investigated by VSM and MFM respectively. We found that such alloy arrays showed strong perpendicular magnetic anisotropy with easy axis parallel to nanowire arrays. Each nanowire was in single domain structure with several opposite single domains surrounding it. Additionally, we investigated the domain structure with a variable external magnetic field applied parallel to the nanowire arrays. The MFM results showed a good agreement with our magnetic hysteresis loop.     

Fabrication and magnetic properties of Fe3O4 nanowire arrays in different diameters

Fe₃O₄ nanowire arrays with different diameters of D=50, 100, 150 and 200 nm were prepared in anodic aluminum oxide (AAO) templates by an electrodeposition method followed by heat-treating processes. A vibrating sample magnetometer (VSM) and a Quantum Design SQUID MPMS magnetometer were used to investigate the magnetic properties. At room temperature the nanowire arrays change from superparamagnetism to ferromagnetism as the diameter increases from 50 to 200 nm. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements show that the blocking temperature T_B increases with the diameter of nanowire. The ZFC curves of D=50 nm nanowire arrays under different applied fields (H) were measured and a power relationship between T_B and H were found. The temperature dependence of coercivity below T_B was also investigated. Mössbauer spectra and micromagnetic simulation were used to study the micro-magnetic structure of nanowire arrays and the static distribution of magnetic moments of D=200 nm nanowire arrays was investigated. The unique magnetic behaviors were interpreted by the competition of the demagnetization energy of quasi-one-dimensional nanostructures and the magnetocrystalline anisotropy energy of particles in nanowires.