纳米Dy0.15Fe1.85O3磁颗粒的低温磁特性研究

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张茂润, 孙静静, 陈静. 纳米Dy_0.15Fe_1.85O₃磁颗粒的低温磁特性研究 . 无机材料学报, 2012, 27(11): 1174-1178
ZHANG Mao-Run, SUN Jing-Jing, CHEN Jing. Study on Magnetic Properties of Dy_0.15Fe_1.85O₃Magnetic Nanoparticles at Low Temperature . Journal of Inorganic Materials, 2012, 27(11): 1174-1178 复制到剪切板

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纳米Dy_0.15Fe_1.85O₃磁颗粒的低温磁特性研究

张茂润, 孙静静, 陈静

安徽理工大学化工学院, 淮南 232001

张茂润(1963-), 男, 副教授. E-mail:Zhangmaor@126.com

基金:安徽省教育厅自然科学基金(2006Kj143B);

摘要

采用共沉淀-相转化法制备了纳米Dy_0.15Fe_1.85O₃磁颗粒, 研究了低温条件下温度变化对其磁学特性的影响. 采用XRF、TEM、XRD和超导量子磁强计(SQUID)对样品的化学成份、形貌、晶型结构和磁学性能进行了表征. 结果表明: 样品中的金属离子主要是Dy³⁺、Fe³⁺, 含量分别为12.17wt%、51.88wt%. 形貌为类球形, 平均粒径约15 nm, 且结晶性完全, 晶型为面心立方尖晶石结构. 在56.5～200.2 K范围内, 样品的饱和磁化强度(M_S)、矫顽力(H_C)均随温度的降低呈现出增大的变化规律, 当温度T≥142.8 K时, 呈超顺磁性状态; 当T<142.8 K时, 由超顺磁性状态转化为铁磁性状态.

关键词: 纳米磁颗粒; 共沉淀-相转化法; 磁学特性; 低温

中图分类号:O654 文献标志码:A 文章编号:1000-324X(2012)11-1174-05

Study on Magnetic Properties of Dy_0.15Fe_1.85O₃Magnetic Nanoparticles at Low Temperature

ZHANG Mao-Run, SUN Jing-Jing, CHEN Jing

School of Chemical Engineering, Anhui University of Science and Technology, Huainan 232001, China

Fund:Natural Science Foundation of Anhui Provincial Education Department (2006Kj143B);

Abstract

Dy_0.15Fe_1.85O₃ magnetic nanoparticles were prepared by coprecipitation-phase transfer method, and the effect of temperature variation on the magnetic properties of the nanoparticles at low temperature were investigated. The chemical composition, morphology, crystalline structure and magnetic properties of the samples at low temperature were characterized by X-ray fluorescence spectrometer(XRF), transmission electron microscope (TEM), X-ray diffraction (XRD) and super-conducting quantum magnetometer (SQUID). The results show that metal ions in the sample are mainly Dy³⁺ and Fe³⁺ whose mass fractions are 12.17% and 51.88%, respectively. The average diameter of the samples isca. 15 nm. The magnetic particles are spherical with face-centered cubic spinel structure and complete crystalline. The saturation magnetization (M_S) and coercivity (H_C) of the samples increase with the decrease of temperature in the range of 56.5 K and 200.2 K. When the temperature exceeds or is equal to 142.8 K, the magnetic properties of the samples is at the superparamagnetic state. While the temperature is below 142.8 K, the superparamagnetic state is converted to ferromagnetic state.

Keyword: magnetic nanoparticles; coprecipitation-phase transfer method; magnetic properties; low temperature

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纳米Fe₃O₄磁颗粒是目前广泛应用的一类纳米磁性材料^{[ 1, 2, 3]}, 具有常规磁性材料所不具备的小尺寸效应、表面效应、超顺磁性等特性, 有关制备方法、性能研究及应用已有很多报道^{[ 4, 5, 6, 7, 8]}. 随着对纳米Fe₃O₄磁颗粒物理、化学性能及磁性能等要求的提高, 它已难以满足不同领域的应用要求. 用d簇过渡元素、稀土元素等金属离子替换Fe₃O₄中的Fe³⁺或Fe²⁺, 提高和改善其电、磁学等性能是主要研究课题之一. 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[ 9, 10, 11, 12, 13, 14]}, 满足了不同领域的应用要求. 由于不同领域对纳米磁性材料的性能要求不同, 因此, 选择的掺杂元素也不同. 稀土Dy³⁺具有独特的4f电子构型和较高的离子磁矩, 对纳米Fe₃O₄磁颗粒进行掺杂, 可以较大幅度地提高其电磁性能和抗氧化性能, 且保持原有的超顺磁特性^{[ 13]}. 纳米掺镝铁氧体在室温下具有超顺磁特性, 当环境温度发生较大改变时, 是否仍具备这一特性及磁性能将如何变化, 对工程应用具有重要的影响. 本研究以硫酸铁、硫酸亚铁、硝酸镝、氢氧化钠为反应原料, 通过共沉淀-相转化法制得纳米Dy_0.15Fe_1.86O₃磁颗粒样品. 并在低温条件下研究了温度因素对磁学特性影响的规律.

1 实验方法

1.1 样品的制备

将原料FeSO₄·7H₂O(AR)、Fe₂(SO₄)₃· xH₂O(AR)、Dy(NO₃)₃· xH₂O(CP)按一定的摩尔比配制成300 mL混合水溶液, 真空过滤后用恒温水浴加热到规定温度, 在电动搅拌条件下将100 mL的 NaOH(AR)溶液(浓度为3.0 mol/L)在1.0 h内加入混合液中, 用数显酸度计观测溶液pH的变化, NaOH溶液滴加完后继续反应0.5 h. 反应结束后, 产物经水洗、离心分离、醇洗, 得无水的湿态磁颗粒样品Ⅰ, 用于XRF、TEM分析.

湿态磁颗粒样品Ⅰ干燥时, 由于乙醇挥发后易产生硬团聚, 为了解决团聚问题, 在反应液中加入0.12 g月桂酸CH₃(CH₂)₁₀COOH(CP), 对生成的磁颗粒表面进行修饰, 产物经水洗、离心分离、真空干燥, 得黑色固态磁颗粒样品Ⅱ, 用于XRD分析和磁性能测试.

1.2 样品的表征

采用ADVANT'XP型X射线荧光光谱仪(美国热电集团瑞士ARL公司)分析样品Ⅰ的化学成分; 采用JEM-100SX型透射电镜(日本JEOL公司)观测样品Ⅰ的形貌和粒径; 采用XD-3射线衍射仪(北京普析通用仪器有限责任公司)分析样品Ⅱ的晶型结构; 采用PPMS-XL5型超导量子磁强计(美国Quantum Design公司)测试样品Ⅱ在低温下的磁性能.

2 结果与讨论

2.1 无水的湿态磁颗粒的XRF分析

样品Ⅰ的XRF分析结果见表1(测试条件: 4GN铑靶、超尖端、超薄窗(75 μm)、端窗X射线管), 由表1可知, 样品中的金属元素主要是Fe和Dy, 其余为少量的Na、Ti、Mg等杂质元素. Dy含量与Fe含量相比较低, 说明Dy³⁺的掺杂量受到了一定限制, 这是由于Dy³⁺的半径与铁氧体晶格中的Fe³⁺、Fe²⁺半径不匹配, 难以实现高浓度的Dy³⁺掺杂. 金属氧化物主要是Fe₂O₃和Dy₂O₃, 样品是Dy(Ⅲ)-Fe(Ⅲ)混合氧化态的化合物.

表1 样品Ⅰ中金属元素及氧化物含量(wt%) Table 1 The content of metal elements and oxide for sampleⅠ(wt%)

2.2 无水湿态磁颗粒的TEM分析

图1(a)为样品Ⅰ的TEM照片, 由图1(a)可以看出, 样品I形貌主要为类球形纳米颗粒, 粒度分布较均匀, 平均粒径约15 nm左右. 图1(b)为样品Ⅰ的SAED图案. 由图1(b)可以看出, 样品I的电子衍射图呈圆环形, 圆环上清晰的亮斑表明产物已经晶化, 且具有较好的晶型.

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	图1 样品Ⅰ的TEM照片(a)和SAED图案 (b)Fig. 1 TEM image (a) and SAED pattern (b) of sampleⅠ

2.3 样品的XRD分析

图2为样品Ⅱ的XRD图谱(测试所用X射线为CuKα射线, 波长 λ=0.154060 nm, 电流40 mA, 电压36 kV, 扫描速度4°/min, 扫描范围为2 θ由5°到70°). 经分析, 其主要衍射峰分布在2 θ=30.32°、35.52°、43.22°、53.34°、56.72°、62.68°, 分别对应反尖晶石型面心立方相Fe₃O₄的 (220)、(311)、(400)、(422)、(511)、(440)的晶面位置, 与标准Fe₃O₄的特征衍射峰符合得较好, 说明样品Ⅱ的晶型为面心立方尖晶石结构; 衍射峰尖锐, 表明颗粒的结晶性完全. 与纯Fe₃O₄衍射峰相比, 在2 θ为21.06°出现的杂峰为少量结晶较好的α-FeOOH.

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	图2 样品Ⅱ的XRD图谱Fig. 2 XRD pattern of sampleⅡ

2.4 温度变化对磁性能的影响

图3(a,b)分别为样品Ⅱ在不同温度下的饱和磁化强度( M_S)和矫顽力( H_C)(测试条件: 磁场强度 H=±1.0 T; 测试温度分别为200.2、171.5、142.8、113.9、85.2、56.5 K). 由图3(a)可以看出, 样品的饱和磁化强度随温度的降低而增大. 温度为56.5 K时, 饱和磁化强度最大, 其值约239.0 mT; 温度为200.2 K时, 饱和磁化强度最小, 其值约212.5 mT. 可见, 温度对饱和磁化强度有重要影响. 这是由于磁颗粒在外界磁场作用下达到磁饱和后, 其内磁矩均沿着接近于外磁场的方向定向排列, 由于热能 k_B T (k_B为玻尔兹曼常数、 T为热力学温度)的作用, 内磁矩时刻产生偏离外磁场方向的振动, 振动幅度的大小取决于 k_B T. 当温度降低时 k_B T减小, 内磁矩偏离外磁场方向的幅度变小, 因此饱和磁化强度增大. 由图3(b)可以看出, 样品的矫顽力也随着温度的降低而增大. 温度为56.5 K时, 矫顽力最大, 其值约8.013 mT; 温度为200.2 K时, 矫顽力最小, 其值约3.824 mT. 因此, 温度同样对矫顽力产生较大的影响. 在低温环境中, 磁颗粒的热能 k_B T较小, 与其磁各向异性能 KV( K为各向异性常数、 V为磁颗粒的体积)的可比性降低, 当外界磁场撤销后, 磁颗粒的热扰动在改变内磁矩的磁化方向时, 由于磁各向异性的反抗而变得很困难, 因此矫顽力较大.

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	图3 样品II 温度变化对饱和磁化强度(a)和矫顽力(b)的影响Fig. 3 Effect of temperature on saturation magnetization (a) and coercivity (b) of sample Ⅱ

2.4 温度变化对磁特性的影响

样品Ⅱ在不同磁场(50~200 mT)和温度(200.2~ 56.5 K)下的磁化强度见图4. 由图4可知, 在相同的温度下, 磁化强度随施加磁场强度的升高而增大;在施加的磁场强度相同时, 磁化强度随温度的降低而增大. 因此, 温度的改变对样品的磁性能有重要影响.

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	图4 样品Ⅱ在不同磁场强度和温度下的磁化强度Fig. 4 Magnetization of sample Ⅱ at different magnetic fields and temperatures

若温度降低至一定值时, 将会出现磁各向异能( kV)大于热能( k_B T), 此时磁颗粒的磁化作用将被固定在各向异性的轻轴上, 当施加磁场撤消后, 剩余磁化强度( M_r)和矫顽力( H_C)不为零, 失去超顺磁性的特性, 此时的温度即为临界温度.

根据超顺磁性理论^{[ 15]}, 超顺磁性体系的磁化强度 M可用Langevin函数表示, 即:

磁颗粒粒径一定时, 其体积 V和饱和磁化强度 M_S为定值. 由Langevin函数可知, M是 H/ T的单值函数, 若将不同磁场强度( H)、温度( T)下测定的磁化强度 M与对应的 H/ T作图, 则磁化强度 M的数据应在同一曲线上, 满足此条件的磁颗粒具有超顺磁性. 反之, 则不具有超顺磁性. 由图4中数据绘制的( H/ T)~ M图见图5, 由图5可以看出, 200.2、171.5、142.8 K时, 在不同磁场强度下测定的 M值近似在同一曲线上(图5中(1)), 说明样品具有超顺磁性; 低于142.8 K时, 测定的 M值在不同的曲线上(图5中(2)、(3)、(4)), 说明样品不具有超顺磁性, 因此, 样品的临界温度约142.8 K. 图5中(1)曲线与Langevin函数曲线有一定的偏离, 是由于应用Langevin函数时, 忽略了磁颗粒间的相互作用, 事实上磁颗粒在单磁畴状态时, 相邻磁颗粒之间会构成异性磁极, 形成表面静磁场, 磁颗粒在静磁场作用下易团聚而形成链结构^{[ 15]}, 使磁化曲线存在微弱的磁滞现象. 此外, 磁颗粒的粒径不均匀, 当一些磁颗粒的粒径大于其临界尺寸时也会产生磁滞现象.

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	图5 样品Ⅱ的( H/ T)- M曲线Fig. 5 ( H/ T)- M curves of sample Ⅱ

3 结论

1)采用共沉淀-相转化法制备掺Dy³⁺铁氧体纳米磁颗粒时, 由于离子半径的不匹配, 难以实现高浓度的Dy³⁺掺杂, 样品主要是Dy(Ⅲ)-Fe(Ⅲ)混合氧化态的化合物.

2)用适量的Dy³⁺对铁氧体进行掺杂, 不会改变铁氧体晶型结构, 样品的晶型为面心立方尖晶石结构.

3)在200.2~56.5 K范围内, 样品的饱和磁化强度( M_S)、矫顽力( H_C)均随温度的降低而增大, 当温度 T≥142.8 K时, 呈超顺磁性状态; 当 T<142.8 K时, 由超顺磁性状态转化为铁磁性状态.

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2008

0.0

0.2735

... 纳米Fe₃O₄磁颗粒是目前广泛应用的一类纳米磁性材料^[1,2,3], 具有常规磁性材料所不具备的小尺寸效应、表面效应、超顺磁性等特性, 有关制备方法、性能研究及应用已有很多报道^[4,5,6,7,8] ...

2010

0.0

Metallie Functional Materials. 2010, 17(1):62-65

Preparation methods of nanosized magnetic fluids

纳米磁性液体具有很多特殊的物化性质,在工业上具有广泛的应用.本文介绍了纳米磁性液体的组成,着重描述了几种常见的纳米磁性液体制备方法,介绍了纳米磁性液体的发展现状,并对今后的发展方向进行了展望.

2010

0.0

0.2735

Journal of Magnetic Materials and Devices. 2010, 41(5):7-11

Magnetic nanoparticles and their applications in biomedicine

磁性纳米颗粒因其独特的超顺磁性质和纳米特性,在生物医学领域得到了日益广泛的应用.本文系统评述了磁性纳米颗粒的制备方法、表面改性及其在生物分离、靶向热疗、靶向给药以及核磁共振成像等生物医学领域中的应用,并对其应用前景进行了展望.

2008

0.0

2009

0.531

1.106

Journal of Inorganic Materials. 2009, 24(4):727-731 DOI:10.3724/SP.J.1077.2009.00727

Study on the synthesis and properties of superparamagnetic monodisperse Fe₃O₄ nanoparticles

National Engineering Research Center for Biomaterials, Sichuan University, Chengdu 610064, China

There are extensive applications for superparamagnetic Fe₃O₄ nanoparticles in the field of biomaterials. Superparamagnetic magnetite nanoparticles coated with oleic acid were prepared in the refluxing mixed system of water, ethanol alcohol and toluene at 74℃. The effect of the OH^- concentration on the surface properties, size, dispersion and magnetic properties of magnetite nanoparticles was studied systematically. The properties of magnetite nanoparticles were tested by X-ray diffraction (XRD), fourier transform infrared (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results show that when the molar ratio of NaOH to Fe(Ⅱ) is less than 8, magnetite nanoparticles coated with oleic acid can be dispersed easily in nonpolar solvents. The addition of NaOH has no obvious influence on the size and the saturation magnetization of magnetite nanoparticles. While the molar ratio of NaOH to Fe(Ⅱ) is more than 8, magnetite nanoparticles can only be dispersed in polar solvents, such as water. Although the saturation magnetization increases to 40A·m²/kg, magnetite nanoparticles are polydisperse and easy to agglomerate in water.

具有超顺磁单分散性的Fe₃O₄磁纳米粒在生物医学材料领域有着广泛的用途. 本研究在水、乙醇和甲苯混合体系74℃回流的条件下制备了具有超顺磁性的表面含油酸的Fe₃O₄磁纳米粒,研究了制备过程中OH^-浓度的变化对磁纳米粒的表面性能、粒径、分散性及磁性能的影响, 并对其机理进行了初步探讨. 采用XRD、FTIR、DLS、TEM和VSM等手段对制备的磁纳米粒进行表征. 结果表明, 当NaOH/Fe(Ⅱ)摩尔比＜8时, Fe₃O₄磁纳米粒表面含油酸可良好地分散于非极性溶剂中, NaOH的加入对磁纳米粒的粒径和饱和磁化强度等性能无明显影响；而当NaOH/Fe(Ⅱ)摩尔比≥8时, Fe₃O₄磁纳米粒仅能分散于水等极性溶剂中, 饱和磁化强度虽可增至40A·m²/kg, 但为多分散且易团聚.

2010

0.72

0.914

Chinese Journal of Inorganic Chemistry. 2010, 26(7):1207-1212

Synthesis of variable-sized Fe₃O₄ nanoerystals and their magnetic properties

This paper described the preparation of variable-sized Fe₃O₄ nanocrystals by air oxidation method under visible light irradiation at room temperature in the presence of trace EDTA, citric acid, tartaric acid, glutamic acid and discussed their magnetic properties. The results showed that adding the complexing agents (EDTA, citric acid, tartaric acid, glutamic acid) could reduce the particle size of Fe₃O₄ and increase the dispersibility of Fe₃O₄ particles under irradiation by visible light. The oxidation rate could be significantly accelerated by visible light in the presence of complexing agents. The rapid oxidation rate was favorable for the decrease of the size of Fe₃O₄ nanocrystals. The size of the Fe₃O₄ nanocrystals about 11.8~29.6 nm was obtained by controlling the intensity of light and concentration of complexing agents at room temperature. The variable-sized Fe₃O₄ nanocrystals exhibited different magnetic properties.

本文用空气氧化法，在可见光作用下，添加配合剂(EDTA、柠檬酸、酒石酸、谷氨酸)在室温进行了不同粒径纳米Fe₃O₄的制备及其磁性能研究。结果表明：在可见光作用下，随EDTA、柠檬酸、酒石酸、谷氨酸等配合剂的添加，得到纳米Fe₃O₄的粒径有所减小、分散性有所提高；配合剂及可见光共存时，体系反应速率得到提高，高的反应速率使纳米Fe₃O₄晶粒减小；控制适当的光照度和添加剂的量，室温可得到11.8~29.6 nm的Fe₃O₄颗粒。不同粒径纳米Fe₃O₄分别呈现出超顺磁性、铁磁性特征。

2009

3.172

0.0

2009

0.0

Trenda in Biotechnolgy. 2009, 27(8):468-476 DOI:10.1016/j.tibtech.2009.04.003

Biomedical applications of distally controlled magnetic nanoparticles

Nano-sized magnetic particles are increasingly being used across a wide spectrum of biomedical fields. Upon functionalization to enable specific binding, magnetic particles and their targets can be conveniently positioned in vitro and in vivo by the distal application of magnetic fields. Furthermore, such particles can be magnetically heated after reaching their in vivo targets, thus inducing localized cell death that has a considerable therapeutic value in, for instance, cancer therapy. In this context, innovative biomedical research has produced novel applications that have exciting clinical potential. Such applications include magnetically enhanced transfection, magnetically assisted gene therapy, magnetically induced hyperthermia and magnetic-force-based tissue engineering, and the principles and utilities of these applications will be discussed here.

2008

0.71

0.0

... 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[9,10,11,12,13,14]}, 满足了不同领域的应用要求 ...

2010

1.363

0.7325

J. Rare Earths. 2010, 28(3):451-455 DOI:10.1016/S1002-0721(09)60132-0

Microwave electromagnetic and absorbing properties of Dy³+ doped MnZn ferrites

Abstract

Dy³⁺ doped Mn-Zn ferrites Mn_0.3Zn_0.7Fe_2–xDy_xO₄x=0, 0.01, 0.02, 0.03, 0.04were prepared by the conventional solid-state reaction. The crystal structure, surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD), scanning electron microscopy(SEM) and network analyzer (Agilent 8722ET). All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03. The average crystallite size was about 44–56 nm. The microwave electromagnetic properties of the samples were studied at the frequency range from 2 GHz to 18 GHz. It was shown that small amounts of Dy³⁺ substitution could adjust microwave electromagnetic parameters magically. The tan δ exhibited a maximal peak when x=0.03, and the peak value was 0.56. It indicated that the microwave electromagnetic loss properties were excellent when x=0.03. Furthermore, the reasons were also discussed using electromagnetic theory. The reflection loss (RL) increased with the Dy³⁺ content when x<0.04. The Mn_0.3Zn_0.7Fe_1.97Dy_0.03O₄ ferrite displayed excellent microwave absorption properties. The frequency (with respect to −10 dB) started from 11.9 GHz, and the bandwidth reached about 3.5 GHz. The peak value of RL was about −20.5 dB at a matching thickness of 2.7 mm.

... 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[9,10,11,12,13,14]}, 满足了不同领域的应用要求 ...

2009

0.0

0.588

... 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[9,10,11,12,13,14]}, 满足了不同领域的应用要求 ...

2008

0.0

Journal of China University of Mining & Technology(Nature Science). 2008, 37(4):499-502

Preparation and photocatalytic activity of magnetic-nanomete CoFe₂O₄/TiO₂ composite materials

JIANG Rong-Li , LIU Yong-Chao , CHEN Wen-Long

... 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[9,10,11,12,13,14]}, 满足了不同领域的应用要求 ...

2010

0.0

1.263

... 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[9,10,11,12,13,14]}, 满足了不同领域的应用要求 ...

... 稀土Dy³⁺具有独特的4f电子构型和较高的离子磁矩, 对纳米Fe₃O₄磁颗粒进行掺杂, 可以较大幅度地提高其电磁性能和抗氧化性能, 且保持原有的超顺磁特性^[13] ...

2007

0.612

0.835

Acta Metallurgica Sinica. 2007, 43(5):529-533

Synthesis of cobalt ferrite nanoparticles in high static magnetic field by coprecipitation- phase transfor mation way

上海大学

Cobalt ferrite nanoparticles were synthesized in high static magnetic field by coprecipitation-phase transform way, and the influences of magnetic flux density(MFD) on the shape and properties of cobalt ferrite nanoparticles was studied through SEM, X-ray diffraction and Vibrating Sample Magnetometer. It was shown that, when without magnetic field or MFD lower than 2Tesla, spheric cobalt ferrite nanoparticles was obtained, and when MFD was equal or above 4Tesla, claviform cobalt ferrite nanoparticles appeared. With the increase of MFD, much claviform cobalt ferrite nanoparticles was obtained, and the crystallization of cobalt ferrite nanoparticles became better, also the magnetic properties such as remanence magnetism, saturation magnetism and squareness ratio were increased remarkably. The remanence magnetism of cobalt ferrite nanoparticles prepared in 10Tesla magnetic field was 15 times to that without magnetic field, and saturation magnetism was elevated by 1.44 times. Based on the theory of magnetic aggregation and critical magnetic domain, the mechanism how the high static magnetic field affect the shape, crystallization degree and magnetic properties of cobalt ferrite nanoparticles by coprecipitation-phase transform way was discussed.

在强磁场下采用共沉淀-相转化法制备出了纳米级的钴铁氧体颗粒，通过SEM，XRD和VSM等分析手段，考察了磁感应强度对纳米钴铁氧体形貌及性能的影响规律。试验结果表明：无磁场及磁感应强度小于2T时，纳米钴铁氧体颗粒为球形形貌；当磁感应强度大于等于4T时，有棒状纳米钴铁氧体形成；随着磁感应强度的增大，棒状纳米颗粒数量增加，纳米钴铁氧体的晶化程度提高，磁性能(Mr、Ms、Mr/Ms)也有大幅度的提高，10T时制备的纳米钴铁氧体颗粒的剩余磁化强度(Mr)比无磁场下制备的钴铁氧体颗粒的剩余磁化强度增加了近15倍，饱和磁化强度(Ms)提高1.44倍。从磁聚合定向生长和临界磁畴角度，分析了强磁场影响共沉淀-相转化法制备的纳米钴铁氧体的形貌、晶化程度及磁性能的机理。

... 近年来, 该领域的学者通过掺杂等方式对纳米Fe₃O₄进行改性, 制备出性能优良的纳米磁性材料^{[9,10,11,12,13,14]}, 满足了不同领域的应用要求 ...

2005

0.0

... 根据超顺磁性理论^[15], 超顺磁性体系的磁化强度M可用Langevin函数表示, 即: ...

... 图5中(1)曲线与Langevin函数曲线有一定的偏离, 是由于应用Langevin函数时, 忽略了磁颗粒间的相互作用, 事实上磁颗粒在单磁畴状态时, 相邻磁颗粒之间会构成异性磁极, 形成表面静磁场, 磁颗粒在静磁场作用下易团聚而形成链结构^[15], 使磁化曲线存在微弱的磁滞现象 ...