共查询到19条相似文献,搜索用时 140 毫秒
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用自旋极化的MS-Xα方法研究了稀土-过渡族化合物SmCo55的电子态密度、自 旋能级劈裂及原子磁矩.研究结果显示,由于化合物中Sm-Co间的轨道杂化效应,使Sm原子原来的5d00空轨道上占据了少量5d电子.由于Co(3d)-Sm(5d)电子间的直接交换作用,导致了Sm-Co间的磁性交换耦合,这是化合物中形成Sm-Co铁磁性长程序的一个重要原因.在SmCo55 sub>化合物中存在6个能级呈现负交换耦合,导致了SmCo55化
关键词:
电子结构
自旋极化
原子磁矩
交换耦合 相似文献
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采用基于第一性原理的全势能线性缀加平面波方法计算闪锌矿结构CaC和SrC的电子结构.计算结果表明,锌矿结构CaC和SrC是自旋向上电子为非金属性的半金属,其半金属隙分别为0.83 eV和0.81 eV.磁性的计算分析表明,CaC和SrC的晶胞总磁矩都为2.00μB,C的原子磁矩较强,Ca和Sr的原子磁矩较弱.使晶格均匀体形变△a/a0限于±15%,在此范围内计算CaC和SrC的电子结构.计算研究表明,当闪锌矿结构CaC和SrC的晶格常数分别为0.490 nm—0.661 nm和0.539 nm—0.707 nm时,它们的半金属性不变,晶胞总磁矩仍然为2.00μB. 相似文献
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采用第一性原理计算方法, 研究了四方MoSi2薄膜的电子性质. 计算结果表明, 各种厚度的薄膜都是金属性的, 并且随着厚度的增加, 其态密度与能带结构都逐渐趋近于MoSi2块体的特性. 通过对MoSi2薄膜磁性的分析, 发现三个原子层厚的薄膜具有磁性, 其原胞净磁矩为0.33 μB; 而当薄膜的厚度大于三个原子层时, 薄膜不具有磁性. 此外, 进一步对单侧加氢饱和以及双侧加氢饱和结构下三原子层MoSi2薄膜的电子性质进行了研究, 发现单侧加氢饱和的三原子层MoSi2薄膜具有磁性, 其原胞净磁矩为0.26 μB, 而双侧加氢饱和三原子层MoSi2薄膜是非磁性的. 双侧未饱和与单侧加氢饱和的三原子层MoSi2薄膜的自旋极化率分别为30%和33%. 这些研究结果表明, 三原子层厚的MoSi2 超薄薄膜在悬空或者生长于基底之上时具有金属磁性, 预示着它在纳米电子学和自旋电子学器件等方面都有潜在的应用前景. 相似文献
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构建只含有一种过渡金属元素的half-Heusler合金VLiBi和CrLiBi.采用第一性原理的全势能线性缀加平面波方法计算half-Heusler合金VLiBi和CrLiBi的电子结构.计算结果表明,VLiBi和CrLiBi是半金属性铁磁体,它们的半金属隙分别是0.25 eV和0.46 eV,晶胞总磁矩分别为3.00 μB和4.00 μB.磁性计算结果显示,晶胞总磁矩主要来源于V和Cr的原子磁矩,Li和Bi的原子磁矩较弱,而且Bi的原子磁矩为负值.利用平均场近似方法计算合金的居里温度TC,VLiBi和CrLiBi的居里温度(TC)的估算值分别为1401 K和1551 K.使晶格常数在±10%的范围内变化,分别计算VLiBi和CrLiBi的电子结构.计算研究表明,晶格常数在-5.6%–10%和-6.9%–10%的范围内变化时VLiBi和CrLiBi仍具有半金属性,并且晶胞总磁矩稳定于3.00 μB和4.00 μB.采用局域密度近似(LDA)+U(电子库仑相互作用项)的方法计算VLiBi和CrLiBi的电子结构,当U的取值增大到5 eV时VLiBi和CrLiBi仍保持半金属性.此外,采用考虑自旋-轨道耦合(spin-orbit coupling,SOC)效应的广义梯度近似(GGA)+SOC方法计算VLiBi和CrLiBi的电子结构,计算结果显示有微弱的自旋向下能带穿过费米能级,此时VLiBi和CrLiBi在费米面处的自旋极化率分别为98.8%和94.3%,它们的晶胞总磁矩分别为3.03 μB和4.04 μB.VLiBi的半金属性几乎不受SOC效应的影响,而CrLiBi在费米面处仍有较高的自旋极化率. 相似文献
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基于密度泛函理论的第一性原理研究赝势平面波方法,计算了碱土金属X(X=Be, Mg, Ca和Sr)掺杂二维单层SnS2的电子结构、磁学性质和光学性质.结果表明:S-rich条件下的体系相较于Sn-rich更稳定,能带结构表明:在Be掺杂后,SnS2体系从自旋向上通道和自旋向下通道完全对称的非磁性半导体转变为具有1.999μB磁矩的磁性半导体.在Mg掺杂后,体系转变为非磁性P型半导体;Ca和Sr两种掺杂体系由于极化程度的不同,导致在下自旋通道的能带穿过费米能级,而在上自旋通道的能带并未穿过费米能级,呈现出磁矩分别为1.973、2.000μB的半金属特性.同时发现X(X=Be, Mg, Ca和Sr)掺杂后,掺杂体系实部静态介电常数大幅度增加,掺杂后的SnS2体系的极化能力增强,虚部数值在低能区明显变大,更适用于长波长光电器. Be, Mg, Ca和Sr掺杂不仅导致吸收边红移,而且提高了红外光区域的有效利用率. 相似文献
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利用密度泛函理论的第一性原理赝势平面波方法,研究过渡金属X(X=Cr、Mn、Fe、Tc、Re)原子掺杂Janus Ga2SSe的磁性、电子性质及光学性质.研究表明:过渡金属掺杂Janus Ga2SSe体系在Chalcogen-rich条件下有着比Ga-rich条件下更好的稳定性.其中Mn掺杂体系形成能在两种条件下皆为最低.本征Ga2SSe是具有2.02 eV带隙的间接带隙半导体,在紫外区域有着很好的光伏吸收能力.与本征Ga2SSe相比,Cr掺杂体系自旋向上通道出现杂质能级,自旋向上与向下通道不对称,呈磁矩为2.797μB铁磁性半金属. Mn掺杂体系在其自旋向上通道产生的杂质能级,呈磁矩为3.645μB的磁性P型半导体. Fe掺杂体系自旋向下通道产生的杂质能级,呈磁矩为3.748μB磁性P型半导体.在Tc与Re掺杂后,带隙皆由间接变直接带隙,呈无磁性的P型半导体.从光学性质来看,各掺杂体系与未掺杂Ga2SSe在介电... 相似文献
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用单辊急冷法制备了非晶态(Fe1-xVx)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2.08μB和-5.08μB。居里温度Tc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: 相似文献
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A. Lappas L. Cristofolini K. Prassides K. Vavekis A. Amato F.N. Gygax M. Pinkpank A. Schenck 《Hyperfine Interactions》1997,105(1-4):101-106
μ+SR and neutron diffraction measurements show that at low temperatures in La1.875 Ba0.125 CuO4, there is phase separation into a long range ordered magnetic component of SDW‐like nature, identified with the LTT phase
and a superconducting component, identified with the LTO phase. Partial substitution of Ba by Sr at a fixed doping level of
1/8 leads to gradual decrease of the magnetic freezing temperature, accompanied by a decrease in the fraction of the magnetic
component. The La1.875 Ba0.025 Sr0.100 CuO_4 composition exhibits freezing of the Cu electronic moments into a disordered arrangement. Excess interstitial oxygen
leads to a rapid recovery of superconductivity and a marked depression of the magnetic volume fraction. Study of the LTT phase
– after stabilisation with partial substitution of La by Nd – away from the 1/8 doping level, reveals no evidence of long
range magnetic ordering with magnetic fluctuations surviving down to 3 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Martin Breza 《Czechoslovak Journal of Physics》1996,46(5):503-507
Electronic structure of La2–x
Ba
x
CuO4 superconductors has been studied. Model systems La10CuO
22
–12
, La10cuO
14
+4
and LagBaCuO
14
+3
with various Ba positions have been investigated using the quasirelativistic INDO molecular orbital method. The oxidation state of copper atoms corresponds to Cu(II). The influence of Ba/La substitution on copper atoms is much lower than on their oxygen ligands sphere. 相似文献
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为阐明磁性离子在不同替代位置对YBCO体系超导电性的影响机制,利用正电子湮没及相关实验手段结合数值模拟,系统研究了Fe和Ni掺杂的YBa2Cu3O7-δ体系. 结果表明,Fe和Ni离子在替代过程中均以离子团簇的形式进入晶格. 当离子进入CuO2面时,由于团簇改变了周围的电子结构,造成电子的局域化,并直接影响了电子对的配对和输运,因而强烈抑制了体系的超导电性.而当掺杂离子进入Cu-O链区时,它们同样通过团簇的形式改变周围
关键词:
YBCO超导体
磁性离子替代
正电子湮没
数值模拟 相似文献
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Junchao Lu Li Pi Shun Tan Yuheng Zhang 《Physica C: Superconductivity and its Applications》2010,470(21):1920-1927
In this paper, the substitution effect of Sr for La in three non-superconducting system La2−xSrxCu0.94M0.06O4 (M = Fe, Co and Ni) have been systematically studied. As the concentration of Sr increases to around 0.20, the superconductivity is recovered. The peak at 695 cm−1 in the infrared spectra which is assigned to the stretching mode of oxygen atoms in plane induced by M3+ doping is suppressed by Sr increasing, demonstrating that the holes introduced by the Sr substitution have been injected into the CuO2 plane and compensate the localized electrons. These results suggest that the superconductivity recurrence is caused by the carrier compensation. The main origin of superconductivity suppression by the magnetic ions Fe/Co/Ni is the carrier localization effect. 相似文献
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K. Kumagai Y. Nakamichi Y. Nakamura I. Watanabe H. Nakajima T. Fujita 《Hyperfine Interactions》1989,50(1-4):583-591
Nuclear quadrupole resonances (NQR) of139La in La2−xMxCuO4 (M=Ba, Sr) and63Cu in YBa2CU3O7 have been investigated with substitution of Cu by magnetic impurities. For La-system, the strong enhancement of the nuclear
relaxation rate, 1/T
1 atT
c
*≈10 K (suggesting the occurrence of magnetic instability with hole-doping), is suppressed by 3D-antiferromagnetism induced
by magnetic impurities. In the superconducting region, fluctuations of Cu moments at low temperatures remain extremely fast
as at high temperatures. For Y-system, Fe-ions are substituted for both Cu(1) and Cu(2) sites, But Co-ions are preferentially
substituted to Cu1 sites. The peaks in the relaxation rate of Cu indicate the appearance of magnetic ordering without destroying
superconductivity for the 0.5%-Fe doped sample. 相似文献
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W. H. Fietz C. A. Wassilew H. A. Ludwig B. Obst C. Politis M. R. Dietrich 《高压研究》2013,33(1-6):423-425
Abstract The results of X-ray investigations of Tl2Ba2Ca2Cu3O10 show a preferential c-axis decrease under high pressure, leading to a bulk modulus of B = 1370 kbar at 300 K. The results are compared to previous investigations of La2CuO4, La1.8Sr0.2CuO4 and Pr2CuO4, that show a similar linear compressibility in a- and b- axis direction. The linear compressibility in c-axis direction is dominated by the degeneration of the Cu-O octohedra and by the compressibility of intercalated layers. 相似文献
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通过测量YBa2Cu3-xMxO7-y(M=Zn,Ni,x=0,0.025,0.05,0.075,0.1,0.15,0.2,0.3)系列样品的晶体结构、正常态电子输运性质、超导电性以及O含量,给出了Zn择优取代Cu(2)的更直接证据;同时,观察到掺Zn系统中的由正交相Ⅰ到正交相Ⅱ的结构相变以及Ni取代Cu带来的电子局域化效应。研究结果表明,具有正二价态的Zn对Cu(2)具有择优取代性,而具有正二价和正三价的Ni并不具有明显的择优取代。对Cu(2)的取代引起超导临界温度的显著变化,但对正常态电子输运性质的影响不明显;对Cu(1)的取代更显著地影响了晶体结构和正常态电子输运性质,同时对Tc产生抑制,我们认为,YBa2Cu307中的高温超导电性以及正常态输运性质是由CU-O平面和Cu-0链共同承担,而Cu-O平面和Cu-0链之间的耦合强度决定着该系统的超导电性的强弱。
关键词: 相似文献
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Vibhav Pandey R.P. Aloysius V.P.S. Awana R.K. Kotnala 《Journal of magnetism and magnetic materials》2009,321(14):2239-2244
The structural magnetic and magneto-transport properties of double perovskite system Ba2−xSrxFeMoO6 (0?x?1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe-Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba2FeMoO6 exhibits saturation magnetic moment value of 3.54 μB/f.u. at 85 K in a magnetic field of 6000 Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73 μB/f.u. and MR value of 7.08% (1 T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail. 相似文献