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1.
We investigate the variations from as-deposited Zn1-x: Cox O magnetic semiconductors to the post-annealed Co- ZnCoO granular composite. The as-deposited Zn1-x Cox 0 magnetic semiconductor deposited under thermal nonequilibrium conditions is composed of Zn1-x. Cox O nanograins of high Co concentration. The room-temperature ferromagnetism with high magnetization and large negative magnetoresistance are found in the as-deposited samples. By annealing, the samples become of granular composite consisting of the Co metal grains and the remanent Zn1-x CoxO matrix. Although the magnetization is enhanced after annealing, the spin-dependent negative magnetoresistance disappears at room temperature. The magnetoresistance observed in the annealed samples in the high field region has no relation with the ferromagnetism, which in turn indicates that the roomtemperature ferromagnetism and large negative magnetoresistance observed in the as-deposited are the intrinsic properties of the Zn1-x Cox O magnetic semiconductor. 相似文献
2.
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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5.
Kongping WuShulin Gu Kun TangJiandong Ye Shunming ZhuMengran Zhou Yourui HuangMingxiang Xu Rong ZhangYoudou Zheng 《Journal of magnetism and magnetic materials》2012,324(8):1649-1654
The influences of Mn doping on the structural quality of the ZnxMn1−xO:N alloy films have been investigated by XRD. Chemical compositions of the samples (Zn and Mn content) and their valence states were determined by X-ray photoelectron spectrometry (XPS). Hall effect measurements versus temperature for ZnxMn1−xO:N samples have been designed and studied in detail. The ferromagnetic transitions happened at different TC should explain that the magnetic transition in field-cooled magnetization of Zn1−xMnxO:N films at low temperature is caused by the strong p-d exchange interactions besides magnetic transition at 46 K resulting from Mn oxide, and that the room temperature ferromagnetic signatures are attributed to the uncompensated spins at the surface of anti-ferromagnetic nano-crystal of Mn-related Zn(Mn)O. 相似文献
6.
T. Wojtowicz W. L. Lim X. Liu G. Cywi
ski M. Kutrowski L. V. Titova K. Yee M. Dobrowolska J. K. Furdyna K. M. Yu W. Walukiewicz G. B. Kim M. Cheon X. Chen S. M. Wang H. Luo I. Vurgaftman J. R. Meyer 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):325
We discuss a new narrow-gap ferromagnetic (FM) semiconductor alloy, In1−xMnxSb, and its growth by low-temperature molecular-beam epitaxy. The magnetic properties were investigated by direct magnetization measurements, electrical transport, magnetic circular dichroism, and the magneto-optical Kerr effect. These data clearly indicate that In1−xMnxSb possesses all the attributes of a system with carrier-mediated FM interactions, including well-defined hysteresis loops, a cusp in the temperature dependence of the resistivity, strong negative magnetoresistance, and a large anomalous Hall effect. The Curie temperatures in samples investigated thus far range up to 8.5 K, which are consistent with a mean-field-theory simulation of the carrier-induced ferromagnetism based on the 8-band effective band-orbital method. 相似文献
7.
C.C. LiB.S. Wang S. LinJ.C. Lin P. TongW.J. Lu Y.P. Sun 《Journal of magnetism and magnetic materials》2011,323(17):2233-2237
The structural, magnetic and electrical transport properties of Zn-doped antiperovskite compounds Ga1−xZnxCMn3 (0≤x≤0.30) have been investigated. After partial substitution of Zn for Ga, the Curie temperature increases monotonously and the ground antiferromagnetic (AFM)-ferromagnetic intermediate (FI) phase transition is gradually suppressed. With increasing the doping level x, the saturated magnetizations decreases gradually firstly for x≤0.20, then increases with increasing x. The electrical transport properties of Ga1−xZnxCMn3 are studied at different magnetic fields. Enhanced giant magnetoresistance (GMR) was observed around the AFM-FI transition. With increasing x, the maximal values and peak widths of GMR increase. Particularly, for x=0.20, GMR reaches a maximum value of 75%, spanning a temperature range of 80 K at 50 kOe and displays the behavior of strongly depending on the magnetization history. The possible origins are discussed. 相似文献
8.
研究磁性半导体中负磁电阻产生机理对正确理解载流子与磁性离子间的sp-d磁交换作用 是非常重要的.通过变温(10---300 K)磁输运和变温(5---300 K)磁化率实验研究了一系列不同Mn含量 非简并p型Hg1-xMnxTe单晶(x>0.17)的负磁电阻和顺磁增强效应. 实验结果表明其负磁电阻与温度的关系和磁化率与温度的关系基本一致, 两者都包含一个呈指数型变化的温度函数exp(-K/T).根据磁性半导体的杂质能级理论, 非简并p型Hg1-xMnxTe单晶在低磁场范围内出现负磁电阻效应的主要物理机理 为外磁场的磁化效应使得受主杂质或受主型束缚磁极化子的有效电离能减小. 相似文献
9.
MgxZn1-xO thin films have been prepared on silicon substrates by radio
frequency magnetron sputtering at 60℃. The thin films have hexagonal
wurtzite single-phase structure and a preferred orientation with the c-axis
perpendicular to the substrates. The refractive indices of MgxZn1-xO films
are studied at room temperature by spectroscopic ellipsometry over the wavelength
range of 400--760\,nm at the incident angle of 70℃. Both absorption
coefficients and optical band gaps of MgxZn1-xO films are determined by
the transmittance spectra. While Mg content is increasing, the absorption edges of
MgxZn1-xO films shift to higher energies and band gaps linearly increase
from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important
information for the design and modelling of ZnO/ MgxZn1-xO heterostructure
optoelectronic devices. 相似文献
10.
Si1−xMnx diluted magnetic semiconductor (DMS) bulks were formed by using an implantation and annealing method. Energy dispersive X-ray fluorescence, transmission electron microscopy (TEM), and double-crystal rocking X-ray diffraction (DCRXD) measurements showed that the grown materials were Si1−xMnx crystalline bulks. Hall effect measurements showed that annealed Si1−xMnx bulks were p-type semiconductors. The magnetization curve as a function of the magnetic field clearly showed that the ferromagnetism in the annealed Si1−xMnx bulks originated from the interaction between interstitial and substitutional Mn+ ions, which was confirmed by the DCRXD measurements. The magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature was approximately 75 K. The present results can help to improve understanding of the formation mechanism of ferromagnetism in Si1−xMnx DMS bulks. 相似文献
11.
研究了溶胶-凝胶法制备氧化物巨磁电阻材料的工艺,制备了La0.7Sr0.3< /sub>CrxMn1-xO3(x=0,0.10,0.15)和La0.7Sr0.3FexMn1-xO3(x=0.05,0.10,0.16)两 系列的单相钙钛矿锰氧化物多晶样品,并研究了Cr,Fe替代La0.7Sr0.3 sub>MnO3中部分Mn后对其结构、磁性和巨磁电阻性质的影响.观察到La0.7 Sr0.3Cr0.15Mn0.85O3和La0. 7Sr0.3Fe0.05Mn0.95O3两个样品的 电阻-温度曲线都出现了双峰.定性讨论了可能产生双峰的机制.随Cr(或Fe)替代量的增加, 材料的居里温度很快下降,铁磁性减弱,导电性降低,巨磁电阻效应增强.但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小.
关键词:
巨磁电阻效应
溶胶-凝胶工艺
电阻-温度曲线
金属绝缘体转变 相似文献
12.
铝掺杂ZnMnO纳米晶体的载流子调控铁磁性 总被引:1,自引:0,他引:1
通过溶胶-凝胶自燃烧技术合成了Zn0.95-xAlxMn0.05O(x=0、0.03、0.05和0.07)稀磁半导体材料. 并且研究了Al掺杂对Zn0.95-xAlxMn0.05O结构、电学和磁学性质的效果. X射线衍射显示合成的组合物为单相六方晶系纤锌矿型晶体结构,类似于氧化锌.显微图像显示颗粒呈团簇状,但一些单个颗粒呈现六角形纹理. 观察到的电阻率随温度升高(达450 oC)而降低,显示为半导体行为特征.所有组合物具有室温铁磁行为. 饱和磁化强度的值随着Al(载流子)浓度的增加而增加. 相似文献
13.
The samples with the Mn3+/Mn4+ ratio fixed at 2:1 La(2+x)/3Sr(1−x)/3Mn1−xCrxO3 (0≤x≤0.20) have been prepared. The magnetic, electrical transport, and magnetoresistance properties have been investigated. Remarkable transport and colossal magnetoresistance (CMR) effect, as well as cluster glass (CG) behaviors have been clearly observed in the samples studied. It was found that the Curie temperature Tc and insulator−metal transition temperature Tp1 are strongly affected by Cr substitution. The experiment observations are discussed by taking into account the variety of tolerance factors t; the effects of A-site radius 〈rA〉 and the A-site mismatch effect (σ2). 相似文献
14.
在白宝石(sapphire)衬底上低温外延生长出了MgxZn1-xO晶体薄膜.x射线衍射(XRD)及能量色散x射线(EDX)分析表明,MgxZn1-xO薄膜的晶体结构依赖于薄膜中Mg的组分x,随着Mg组分的增大,MgxZn1-xO薄膜的结构从与ZnO晶体一致的六方结构转变为与MgO晶体一致的立方结构.对MgxZn1-xO薄膜的紫外透
关键词:
电子束蒸发反应
xZn1-xO晶体薄膜')" href="#">MgxZn1-xO晶体薄膜
结构和光学性能 相似文献
15.
The effect of cobalt-doping on the magnetic, transport and magnetoresistance characteristics of La1-xSrxMnO3 was investigated. The results show that the magnetoelectric property of
rare-earth doped manganites is greatly affected by substitution of Co for Mn sites. The Curie temperature as well as the magnetic moment decreases with the increase of doping concentration, and the samples exhibit obvious characteristics of the spin glass state. Moreover, the magnetoresistance is evidently modulated by doping concentration,
and the relevant temperature dependence is also suppressed. In addition, low-temperature magnetoresistance is significantly
promoted as doping concentration increases, which renders a value of approximately 50% in the temperature range of 5--200~K and varies within 12.5%. It can be attributed to the effect of spin scattering, induced by cobalt doping, on the itinerant electrons of Mn ions, thus introducing a spin-disorder region into the ferromagnetic region of double-exchange interaction between neighbouring Mn3+ and Mn 3+ ions. 相似文献
16.
利用脉冲激光沉积方法在Si(100)上制备了Cox-C1-x颗粒膜,并研 究了其正磁电阻 效应.实验结果表明,样品在室温下的正磁电阻效应要远远高于低温下的正磁电阻效应;Co 0.02-C0.98样品具有最大的室温正磁电阻效应,在外加磁场B=1T时 ,其磁电阻 率MR=22%;随着Co含量的增加,Cox-C1-x颗粒膜的正磁电阻效应呈 减小趋势.样品 的MR-B的曲线与传统的多
关键词:
正磁电阻效应
x-C1-x颗粒膜')" href="#">Cox-C1-x颗粒膜
脉冲激光沉积 相似文献
17.
First-principles study of structrural and corrected band properties of wurtzite Zn1-xCdxO and Zn1-xMgxO systems
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A first-principles method based on density functional theory(DFT),a generalized gradient approximation(GGA),and a projector-augmented wave(PAW) are used to study the structual and band properties of wurtzite Zn1-xCdxO and Zn1-xMgxO(0 ≤x≤1) ternary alloys.By taking into account all of the possible structures,the band gaps of Zn1-xCdxO and Zn1-xMgxO alloys are corrected and compared with experimental data. 相似文献
18.
W. Zhong W. Chen H.Y. Jiang X.S. Liu C.T. Au Y.W. Du 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):331-337
Polycrystalline two-layered perovskite La2.5-xK0.5+xMn2O
7 + δ
(0 <
x
< 0.5) samples have been prepared by a modified sol-gel method and their magnetoresistance and magnetocaloric effects have been
studied. A large deviation between the metal-insulator (MI) transition temperature (T
ρ
) and the magnetic transition temperature (TC) is observed. Large magnetoresistance (MR) effects with Δρ/ρ
of ∼40% at 12 kOe are obtained in wide temperature ranges. The maximum of the magnetic entropy change peaks at its Curie temperature
(TC), far above its MI transition temperature (T
ρ
). The large magnetic entropy change (∼1.4 J/kg.K) is obtained in the sample La2.5-xK0.5+xMn2O
7 + δ
(x
= 0.35) upon 10 kOe applied magnetic field.
Received 2 May 2002 / Received in final form 1st October 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: wzhong@ufp.nju.edu.cn 相似文献
19.
用射频磁控溅射法在80℃的衬底温度下制备出MgxZn1-xO(0≤x ≤030)薄膜.x射线 衍射(XRD)结果表明,MgxZn1-xO薄膜为单相六角纤锌矿结构, 没有形成任何显著 的MgO分离相,MgxZn1-xO薄膜的择优取向平行于与衬底垂直的 c轴;c轴晶格常数随着Mg含量的增加逐渐减小.在MgxZn1-xO薄膜的光透射谱中出现 锐利的吸收边,由透 射谱估算出MgxZn1-xO薄膜的带隙宽度由332eV(x=0)线性地 增加到396eV(x=030).
关键词:
xZn1-xO薄膜')" href="#">MgxZn1-xO薄膜
射频磁控溅射
Mg含量 相似文献
20.
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