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通过X射线衍射及磁测量手段研究了Er2AlFe16-xMnx(x=1,2,3,4,6,8)化合物的结构和磁性. 研究结果表明Er2AlFe16-xMnx化合物具有六角相的Th2Ni17型结构. 采用X射线热膨胀测定法在103—654K的温度范围内测量了Er2AlFe16-xMnx(x=1,2,3,4)化合物的热膨胀性质,发现这些化合物在低温下存在热膨胀反常现象,在居里点附近具有负膨胀性质. 对自发磁致伸缩的研究结果表明Er2AlFe16-xMnx化合物中存在着较强的各向异性的自发磁致伸缩,低温下自旋重取向的出现使得化合物的自发体磁致伸缩有所增强. 磁测量结果表明Mn的替代导致Er2AlFe16-xMnx化合物的居里温度及自发磁化强度急剧下降,并且使得化合物的磁晶各向异性发生显著改变.
关键词:
2AlFe16-xMnx化合物')" href="#">Er2AlFe16-xMnx化合物
反常热膨胀
自发磁致伸缩 相似文献
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用超导量子干涉器(SQUID)磁强计对稀释磁性半导体Zn1-xMnxSe(0.1≤x≤0.50)的低温低场直流磁化率作了测量,测量温度从4.2K到30K,测量磁场为15Oe。当x≥0.30时,从磁化率-温度曲线的浑圆峰值,观察到了自旋玻璃的转变。自旋玻璃的转变温度Tf,对x=0.30,0.40,0.50,分别为10.5K,16K,19.5K。给出了顺磁相和自旋玻璃相的相图。比较了Zn1-xMnxSe和Cd1-xMnxSe的自旋玻璃转变温度,发现对同样的Mn离子浓度,Zn1-xMnxSe的Tf高于Cd1-xMnxSe的Tf,用交换作用的理论作了讨论。
关键词: 相似文献
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通过X射线衍射及磁测量手段研究了Dy2AlFe16-xMnx化 合物的结构和磁性.研究结果表明Dy2AlFe16-xMnx化合 物具有六角相的Th2Ni17型结构.对x=1,2的样品采用X射线热膨胀 测定法在104—647K的温度范围内测量了其热膨胀性质,发现这些化合物在低温下存在热膨 胀反常现象,在居里点附近出现负膨胀性质.对自发磁致伸缩的研究结果表明Dy2AlFe16-xMnx化合物中存在着较强的各向异性的自发磁致伸缩,随 着Mn含量的增加,其低温下的自发体磁致伸缩减弱.磁测量结果表明Mn的替代导致Dy2< /sub>AlFe16-xMnx化合物的居里温度及自发磁化强度急剧下降.
关键词:
2AlFe16-xMnx化合物')" href="#">Dy2AlFe16-xMnx化合物
反常热膨胀
自发磁致伸缩
自发磁化强度 相似文献
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采用溶胶-凝胶法制备了单轴M型锶铁氧体SrFe12-x12-xCrxxO 1919(x=0—1)超细晶粒.实验结果表明, 随掺杂量x的增大,质量饱和磁化强 度σss在x≤04范围内增大,在x=02附近达到极大值.矫顽力Hcc在x<05的范围 内单调降低,这对于用作高密度磁记录材料非常有利.当x≤04时,样品是单相结构, 在 x=06以后出现非磁性相α-Fe22O3<
关键词:
锶铁氧体
3+')" href="#">Cr3+3+
结构
磁性 相似文献
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研究了钙钛矿型锰氧化物La2/3Ca1/3Mn1-xTixO3(0≤x≤0.3)的结构、磁性和输运性质.发现Ti替代Mn强烈地抑制了La2/3Ca1/3MnO3的铁磁性和金属电导,并很大地提高了磁电阻值.在低掺杂情况下(x≤0.04),1%的Mn被Ti替代,居里温度TC和金属-绝缘体转变温度Tp分别平均下降了31和26.5K.当x=0.06时,铁磁态过渡为团簇玻璃态,并在x=0.20时完全变为自旋玻璃态.指出由于Ti的掺入而引起的磁稀释作用以及局域晶格畸变是产生上述结果的主要原因.
关键词: 相似文献
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利用固相反应法在700℃—1000℃不同的温度下、空气中烧结Co3O4 和TiO2混合物,制备了(Co3O4)x/3(TiO2)1-x(03,说明Co3O4与TiO2反应形成了CoT iO3;同时,在700 ℃低温和900 ℃以上的高温烧结样品中分别观察到了单相的 锐钛矿和金红石相结构.经高低温烧结的样品在500 ℃氢退火后,CoTiO3相消失 ,锐钛矿相的CoxTi1-xO2-δ形成.X射线光电子能谱(X PS)分析显示,氢退火样品中的Co以+2氧化价态存在,同时没有观察到金属态的Co,这说明 氢退火样品中的室温铁磁性不是源于金属Co颗粒的形成,而是与钙钛矿结构的CoTiO3< /sub>相的消失和锐钛矿型的CoxTi1-xO2-δ相的形成 有关.(Co3O4)x/3(TiO2)1-x( 0x Ti1-xO2-δ相的本征铁磁性,伴随着结构相变而产生的Co离子之间的铁磁交换相互作用或 许是样品室温铁磁性产生的根本原因.
关键词:
室温铁磁性
结构相变
锐钛矿
氢退火 相似文献
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Ajay Kaushal 《Physica B: Condensed Matter》2009,404(20):3732-3738
Sn1−xMnxO2 (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn1−xMnxO2 thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn3+ ions have substituted Sn4+ ions without changing the tetragonal rutile structure of pure SnO2. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn1−xMnxO2 (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10−4 emu saturation magnetization and 92 Oe coercivity in case of Sn1−xMnxO2 (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration. 相似文献
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A.M. Abdel Hakeem 《Journal of magnetism and magnetic materials》2012,324(1):95-99
The microstructure and magnetic properties have been investigated systematically for Sn1−xMnxO2 polycrystalline powder samples with x=0.02-0.08 synthesized by a solid-state reaction method. X-ray diffraction revealed that all samples are pure rutile-type tetragonal phase and the cell parameters a and c decrease monotonously with the increase in Mn content, which indicated that Mn ions substitute into the lattice of SnO2. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism. Furthermore, magnetic investigations demonstrate that magnetic properties strongly depend on doping content, x. The average magnetic moment per Mn atom decreases with increase in the Mn content, because antiferromagnetic super-exchange interaction takes place within the neighbor Mn3+ ions through O2− ions for the samples with higher Mn doping. Our results indicate that the ferromagnetic property is intrinsic to the SnO2 system and is not a result of any secondary magnetic phase or cluster formation. 相似文献
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S.A. Ahmed 《Solid State Communications》2010,150(43-44):2190-2193
We report here observation of ferromagnetism in pure and Mn doped SnO2 powder with different Mn contents. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism (RTFM), which is identified as an intrinsic characteristic. The RTFM has been observed in the pure SnO2 powder, which is believed to be defect induced, with a saturation magnetization of ~0.017 emu/g. The RTFM was enhanced considerably in the Mn doped samples and the magnetic properties strongly depend on doping content. A sample with 1% of Mn is ferromagnetic at room temperature with a saturation magnetization of ~0.98 emu/g, a remanent magnetization of ~27%, and a coercivity of ~270 Oe. The average magnetic moment per Mn atom decreases with increasing Mn content. Our results reveal that the large RTFM observed in Mn doped SnO2 powder originates from a combination effect of oxygen vacancies and transition metal doping. 相似文献
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采用密度泛函理论结合投影缀加波(PAW)方法,研究了具有钙钛矿结构的BiFeO3材料及对BiFeO3进行B位Co元素替代掺杂得到的BiFe075Co025O3材料的磁结构、电子结构、能带结构.结果表明:Co的掺入不破坏原有的钙钛矿结构,对材料铁电性影响不大;掺杂导致原有的G型反铁磁序发生变化,形成了亚铁磁序的磁结构,材料的铁磁性有了很大提高;然而,Co杂质的掺入使材料的绝缘性有所减弱.
关键词:
第一性原理计算
3')" href="#">Co掺杂BiFeO3
铁磁性 相似文献
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采用柠檬酸溶胶凝胶和放电等离子烧结制备了Ca位双掺杂型的BaxAgyCa3-x-yCo4O9烧结体,利用X射线衍射仪、扫描电子显微镜、电阻率测试仪等研究了烧结体相组成、取向度、织构及电性能.结果表明:含Ag的掺杂试样中出现了偏离化学计量比分布的Ag单质,掺杂试样取向度随Ba与Ag掺杂量之比x/y的增大而提高,含Ag的掺杂试样取向度低于未掺杂试样,不含Ag的掺杂试样取向度高于未掺杂试样.x=y=01的试样导电机理发生变化.Ba,Ag掺杂量相等的试样保持较低取向度的同时具有较低的电阻率,在973 K时达到最低值(73 mΩcm),而取向度最低的Ag单掺杂试样电阻率在所有试样中最低,在973 K时为63 mΩcm.
关键词:
3Co4O9')" href="#">Ca3Co4O9
双掺杂
织构
电输运性能 相似文献
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Shalendra Kumar S. GautamG.W. Kim Faheem AhmedM.S. Anwar K.H. ChaeH.K. Choi H. ChungB.H. Koo 《Applied Surface Science》2011,257(24):10557-10561
We report structural, magnetic and electronic structure study of Mn doped TiO2 thin films grown using pulsed laser deposition method. The films were characterized using X-ray diffraction (XRD), dc magnetization, X-ray magnetic circular dichroism (XMCD) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase related to Mn metal cluster or any oxide phase of Mn. Magnetization studies reveal that both the films (3% and 5% Mn doped TiO2) exhibit room temperature ferromagnetism and saturation magnetization increases with increase in concentration of Mn doping. The spectral features of XMCD at Mn L3,2 edge show that Mn2+ ions contribute to the ferromagnetism. NEXAFS spectra measured at O K edge show a strong hybridization between Mn, Ti 3d and O 2p orbitals. NEXAFS spectra measured at Mn and Ti L3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO2 films. 相似文献
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Preparation, structure and ferromagnetic properties of the nanocrystalline Ti1-xMnxO2 thin films grown by radio frequency magnetron co-sputtering 下载免费PDF全文
This paper reported that the Mn-doped TiO2 films were prepared by radio frequency (RF) magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 (x = 0.21) films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4+ for Ti^4+ into the TiO2 crystal .lattice, and could be explained by O vacancy (Vo)-enhanced ferromagnetism model. 相似文献
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利用第一性原理计算得到C掺杂ZnO的电子结构,发现系统具有半金属的电子结构.从态密度的分析可以看到Zn-3d和C-2p电子具有强烈的杂化作用,这是体系具有相对稳定铁磁基态的原因.利用第一性原理得到的磁性耦合强度并结合蒙特卡罗模拟得到了C掺杂浓度为555%,833%,125%的ZnO1-xCx分别具有210 K,260 K,690 K的居里温度.同时,详细地分析了C掺杂引起的电子转移和C,Zn,O的s,p和d电子的自旋向上和自旋向下电子数的变化.通过比较研究,发现ZnO1-xCx的局域磁矩主要来源于Zn-3d 电子和C-2p 电子之间的相互作用,而局域磁矩耦合倾向于RKKY耦合.
关键词:
1-xCx')" href="#">ZnO1-xCx
磁性
第一性原理
蒙特卡罗模拟 相似文献
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A. Fakhim Lamrani M. Belaiche A. Benyoussef A. El Kenz E.H. Saidi 《Journal of magnetism and magnetic materials》2011,323(23):2982-2986
Using the augmented spherical wave method, the electronic structure and magnetic properties of the rutile SnO2 doped with single and double impurities: Sn1−xMnxO2, Sn1−xWxO2, and Sn1−2xMnxWxO2 with x=0.0625, have been studied. The scalar-relativistic implementation with a generalized gradient approximation functional has been used for treating the effects of exchange and correlation. The ground state of Mn-, and W-doped SnO2 systems have a total magnetic moments of 3 and 2 μB, respectively. The half-metallic nature appears in Sn1−2xMnxWxO2, which makes them suitable as spintronic systems with total magnetic moment of 5 μB. The advantages of doping SnO2 with double impurities are investigated in this work. The total moment of the system, the local magnetic moments of the impurities, and their oxidation states are also discussed. Since there are two possible couplings between the impurities, we studied both configurations (ferromagnetic and antiferromagnetic) for double-impurities-doped SnO2. Magnetic properties and interatomic exchange have been computed for various distances between Mn and W. The indirect exchange between double impurities has similarities with the Zener mechanism in transition metal oxides. Based on the interaction between localized moments, via hybridization between impurities orbitals with the host oxygen, a double exchange mechanism is proposed to explain the ferromagnetism of our system. 相似文献