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1.
This paper reports that (Ga, Mn)N is prepared using implantation of 3at.% Mn Ions into undoped GaN. Structural characterization of the crystals was performed using x-ray diffraetion(XRD). Detailed XRD measurements have revealed the characteristic of Mn-ion implanted GaN with a small contribution of other compounds. With Raman spectroscopy measurements, the spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 747, 733 and 566 cm-1 identified as EI(LO), A1 (LO) and E~, respectively. The Mn-doped GaN layers exhibit additional excitations at 182, 288, 650 725, 363, 506cm^-1 and the vicinity of E~ mode. The modes observed at 182, 288, 650 725em 1 are assigned to macroscopic disorder or vacancy-related defects caused by Mn-ion implantation. Other new phonon modes are assigned to Mnx-Ny, Gax-Mny modes and the local vibrational mode of Mn atoms in the (Ga, Mn)N, which are in fair agreement with the standard theoretical results. 相似文献
2.
Kongping Wu Shulin Gu Kun Tang Shunming Zhu Mengran Zhou Yourui Huang Mingxiang Xu Rong Zhang Youdou Zheng 《Physica B: Condensed Matter》2012,407(13):2429-2433
Mn doped Zinc oxide (ZnO) thin films were prepared by metal organic chemical vapor deposition (MOCVD) technique. Structural characterizations by X-ray diffraction technique (XRD) and photoluminescence (PL) indicate the crystal quality of ZnO films. PL and Raman show a large fraction of oxygen vacancies (VO2+) are generated by vacuum annealed the film. The enhancement of ferromagnetism in post-annealed (Mn, In) codoped ZnO could result from VO2+ incorporation. The effect of VO2+ on the magnetic properties of (Mn, In) codoped ZnO has been studied by first-principles calculations. It is found that only In donor cannot induce ferromagnetism (FM) in Mn-doped ZnO. Besides, the presence of VO2+ makes the Mn empty 3d-t2g minority state broadened, and a t2g-VO2+ hybrid level at the conduction band minimum forms. The presence of VO2+ can lead to strong ferromagnetic coupling with the nearest neighboring Mn cation by BMP model based on defects reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Mn 3d electrons trapped in oxygen vacancies. 相似文献
3.
B. HuB.Y. Man C. YangM. Liu C.S. ChenX.G. Gao S.C. XuC.C. Wang Z.C. Sun 《Applied Surface Science》2011,258(1):525-529
Mn-doped GaN films (Ga1−xMnxN) were grown on sapphire (0 0 0 1) using Laser assisted Molecular Beam Epitaxy (LMBE). High-quality nanocrystalline Ga1−xMnxN films with different Mn concentration were then obtained by thermal annealing treatment for 30 min in the ammonia atmosphere. Mn ions were incorporated into the wurtzite structure of the host lattice by substituting the Ga sites with Mn3+ due to the thermal treatment. Mn3+, which is confirmed by XPS analysis, is believed to be the decisive factor in the origin of room-temperature ferromagnetism. The better room-temperature ferromagnetism is given with the higher Mn3+ concentration. The bound magnetic polarons (BMP) theory can be used to prove our room-temperature ferromagnetic properties. The film with the maximum concentration of Mn3+ presents strongest ferromagnetic signal at annealing temperature 950 °C. Higher annealing temperature (such as 1150 °C) is not proper because of the second phase MnxGay formation. 相似文献
4.
S. Munawar Basha S. Ramasubramanian R. Thangavel M. Rajagopalan J. Kumar 《Journal of magnetism and magnetic materials》2010,322(2):238-241
Investigations have been carried out to study the ferromagnetic properties of transition metal (TM) doped wurtzite GaN from first principle calculations using tight binding linear muffin-tin orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in nickel doped GaN with a magnetic moment of 1.13 μB for 6.25% of Ni doping and 1.32 μB for 12.5% of nickel doping, there is a decrease of magnetic moment when two Ni atoms are bonded via nitrogen atom. The Ga vacancy (VGa) induced defect shows ferromagnetic state. Here the magnetic moment arises due to the tetrahedral bonding of three N atoms with the vacancy which is at a distance of 3.689 Å and the other N atom which is at a distance of 3.678 Å .On the other hand the defect induced by N vacancy (VN) has no effect on magnetic moment and the system shows metallic character. When Ni is introduced into a Ga vacancy (VGa) site, charge transfer occur from the Ni ‘d’ like band to acceptor level of VGa and formed a strong Ni–N bond. In this Ni–VGa complex with an Ni ion and a Ga defect, the magnetic moment due to N atom is 0.299 μB .In case of Ni substitution in Ga site with N vacancy, the system is ferromagnetic with a magnetic moment of 1 μB. 相似文献
5.
Luyan Li Yahui Cheng Weihua Wang Shiwei Ren Yitong Yang Xiaoguang Luo Hui Liu 《Solid State Communications》2011,151(21):1583-1587
The ferromagnetic properties of Mn- and Co-doped Cu2O with copper and oxygen vacancies (VCu and VO) are studied by first-principles calculations. The results indicate that Mn-doped Cu2O has an antiferromagnetic state in the near configuration, while it has a ferromagnetic state for the far configuration. On the contrary, Co-doped Cu2O possess a ferromagnetic state regardless of the distance between the two Co atoms. The observed ferromagnetism can be attributed to the 90° ferromagnetic super-exchange mechanism. The presence of VO can enhance the ferromagnetism, whereas VCudepresses it. 相似文献
6.
Daqing Xu Yimen Zhang Yuming Zhang Peixian Li Chao Wang 《Journal of magnetism and magnetic materials》2009,321(16):2442-2445
Manganese ions were implanted into unintentionally doped GaN epilayers grown by metal organic chemical vapor deposition (MOCVD). The (Ga,Mn)N and GaxMny phases were formed after Mn-implanted undoped GaN epilayers annealed at 700 and 800 °C. The samples showed ferromagnetic behavior at room temperature with the highest magnetization obtained in the sample annealed at 800 °C. Ferromagnetic signal reduces as annealing temperature increased above 900 °C. It is believed that the room-temperature ferromagnetic property of Mn-implanted undoped GaN epilayers are mainly from (Ga,Mn)N. The GaxMny phases play a critical role in providing holes and also contribute to increasing the ferromagnetic property. 相似文献
7.
O. Mounkachi A. Benyoussef A. El Kenz E.H. Saidi E.K. Hlil 《Journal of magnetism and magnetic materials》2008
Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), we investigated the magnetic and half-metallic properties of Mn-doped p-type ZnO and the mechanism which control these properties. Mn-doped ZnO is anti-ferromagnetic spin-glass state, but it becomes half-metallic ferromagnetic upon holes doping. The electronic structure, total magnetic moment of Zn0.8Mn0.2O1−yNy and magnetic moments of Mn and N in Zn0.8Mn0.2O1−yNy are calculated for different holes (y) concentrations. In this paper we address the origin of half-metallic and ferromagnetic properties as controlled and oriented by the nature of hybridization of the Mn (3d) state and host p(N) states. The band structure has been used to explain the strong ferromagnetism observed in Zn0.8Mn0.2O0.1N0.9. 相似文献
8.
An X-ray diffraction study indicates that nonstoichiometric vanadium monoxide VO
y
≡ V
x
O
z
(y = z/x) has a cubic structure of the DO3 type (space group Fm
$
\bar 3
$
\bar 3
m), where vanadium atoms are not only at the 4(a) sites of the metal fcc sublattice, but also at the tetrahedral 8(c) sites. This circumstance fundamentally distinguishes monoxide VO
y
from strongly nonstoichiometric MX
y
compounds with the B1 structure and the same space group, where atoms M and X and structural vacancies ▪ and ▭ of the metal and nonmetal sublattices,
respectively, are distributed over the 4(a) and 4(b) sites. The dependence of the filling factor q of the tetrahedral interstices by vanadium atoms on the relative content y of oxygen in VO
y
has been obtained. It has been shown that the composition of cubic vanadium monoxide should be represented as VO
y
≡ V
x
O
z
≡ V
x − 2q
V2q
(t)▪1 − x + 2q
O
z
▭1 − z
, taking into account the structure. 相似文献
9.
Khang Hoang 《固体物理学:研究快报》2015,9(12):722-725
Understanding the luminescence of GaN doped with erbium (Er) requires a detailed knowledge of the interaction between the rare‐earth dopant and the nitride host, including intrinsic defects and other impurities that may be present in the host material. We address this problem through a first‐principles hybrid density functional study of the structure, energetics, and transition levels of the Er impurity and its complexes with N and Ga vacancies, substitutional C and O impurities, and H interstitials in wurtzite GaN. We find that, in the interior of the material, ErGa is the dominant Er3+ center with a formation energy of 1.55 eV, ErGa–VN possesses a deep donor level at 0.61 eV which can assist in the transfer of energy to the 4f ‐electron core. Multiple optically active Er3+ centers are possible in Er‐doped GaN. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
10.
A. V. Pashchenko V. P. Pashchenko A. G. Sil’cheva V. K. Prokopenko A. A. Shemyakov Yu. F. Revenko V. P. Komarov S. V. Gorban’ 《Physics of the Solid State》2011,53(2):309-315
The structure and properties of lanthanum strontium manganite perovskites La0.6Sr0.2Mn1.2 − y
Cr
y
O3 ± δ (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic (χac and 55Mn NMR) methods. The parameter of the rhombohedrally distorted (R
$
\bar 3
$
\bar 3
c) perovskite structure decreases with increasing y. The real perovskite structure contains point (anion and cation vacancies) and cluster-type nanostructure defects. The analysis
of asymmetrically broadened 55Mn NMR spectra has confirmed the high-frequency electron-hole exchange Mn3+ ↔ Mn4+ and local inhomogeneity of their surrounding by other ions and point and cluster-type defects. An increase in the Cr content
leads to an increase in the resistivity and the magnetoresistive effect and a decrease in the metal-semiconductor and ferromagnetic-paramagnetic
phase transition temperatures (T
ms
and T
c
) due to the distortion of the exchange interactions Mn3+ ↔ Mn4+ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation
energy. The magnetoresistive effect near T
ms
and T
c
is caused by scattering of charge carriers from intercrystallite nanostructure inhomogeneities of the lattice, and the low-temperature
effect is associated with the tunneling on mesostructural intercrystallite boundaries. 相似文献
11.
Well-aligned ZnO nanorods and Mn-doped ZnO nanorods are fabricated on Si (1 0 0) substrate according to the contribution of Zn metal catalysts. Scanning electron microscopy and high-resolution transmission electron microscopy images indicate that the influence of Zn catalyst on the properties of ZnO can be excluded and the growth of ZnO nanorods follows a vapor-liquid-solid and self-catalyzed model. Mn-doped ZnO nanorods show a typical room temperature ferromagnetic characteristic with a saturation magnetization (MS) of 0.273μB/Mn. Cathodoluminescence suggests that the ferromagnetism of Mn-doped ZnO nanorods originates from the Mn2+-Mn2+ ferromagnetic coupling mediated by oxygen vacancies. This technique provides exciting prospect for the integration of next generation Si-technology-based ZnO spintronic devices. 相似文献
12.
用固相反应法制备了La0.45Ca0.55Mn1-xVxO3(x=0.00,0.10)多晶样品.通过X射线衍射谱、质量磁化强度-温度曲线、电子自旋共振谱,研究了V5+替代Mn3+/Mn4+对La0.45Ca0.55MnO3电荷有序相和自旋玻璃态的影响.实验结果表明,当x=0.10时,不仅母体的电荷有序相基本破坏,而且母体在40K左右出现的自旋玻璃态也被融化.电荷有序相被破坏的主要原因是用V5+替代Mn3+/Mn4+后,增加了Mn3+与Mn4+的比例,使铁磁双交换作用优于反铁磁超交换作用;自旋玻璃态的融化是由于V替代Mn后破坏了反铁磁背景下有少量铁磁成分的自旋玻璃态的形成条件. 相似文献
13.
We report a study of the Mn local structure, magnetism, and Ga moments in molecular beam epitaxy grown Mn-doped GaN films. Using x-ray absorption spectroscopy and magnetic circular dichroism, we find two distinct Mn sites and a Ga moment antiparallel to Mn. First-principles calculations reproduce this phenomenology and indicate that Mn preferentially populates Ga sites neighboring N split interstitial defects. These results show that defects may strongly affect the Mn ordering and magnetism, and that the GaN valence band is polarized, providing a long-range ferromagnetic ordering mechanism for Ga1-xMnxN. 相似文献
14.
Chuanfu Huang 《Phase Transitions》2019,92(2):164-171
Here, La-doped Bi1–xLaxFeO3 and Mn-doped BiFe1–yMnyO3 (x, y?=?0.1, 0.2, 0.3) nanoparticles were synthesized by a sol–gel process. For Bi1–xLaxFeO3, structural analysis suggested that its structure changed from rhombohedral to tetragonal phase without secondary phase when x increased from 0 to 0.3. In addition, with the increasing doping concentration of La, transmission electron microscopy exhibited the doped nanoparticle size reduced, while the magnetic properties were correspondingly enhanced. However, for synthesis of BiFe1–yMnyO3, phase analysis showed that there easily existed secondary phase for nanoparticles with 10% and 30% Mn-doped, while 20% Mn-doped nanoparticles indicated high crystallinity without any impure phases. Similarly, we observed the enhanced magnetic properties with the increase of Mn concentration. 相似文献
15.
The magnetic and electrical properties of nonmagnetic Ga +3 ion substitution for Mn site are investigated in the bilayer manganite La 1.2 Sr 1.8 Mn 2 O 7.When the Mn is substituted by Ga,the ferromagnetic property obviously weakens,the magnetic transition temperature decreases and a spin-glass behaviour occurs at low temperature.Meanwhile,doping causes the resistivity to dramatically increase,the metal-insulator transition temperature to disappear,and a greater magneto-resistance effect to occur at low temperature.These effects result from the fact that Ga substitution dilutes the magnetic active Mn-O-Mn network and weakens the double exchange interaction,and further suppresses ferromagnetic ordering and metallic conduction. 相似文献
16.
L. Jeuvrey O. PeñaA. Moure C. Moure 《Journal of magnetism and magnetic materials》2012,324(5):717-722
Single-phase hexagonal-type solid solutions based on the multiferroic YMnO3 material were synthesized by a modified Pechini process. Copper doping at the B-site (YMn1−xCuxO3; x<0.15) and self-doping at the A-site (Y1+yMnO3; y<0.10) successfully maintained the hexagonal structure. Self-doping was limited to y(Y)=2 at% and confirmed that excess yttrium avoids formation of ferromagnetic manganese oxide impurities but creates vacancies at the Mn site. Chemical substitution at the B-site inhibits the geometrical frustration of the Mn3+ two-dimensional lattice. The magnetic transition at TN decreases from 70 K down to 49 K, when x(Cu) goes from 0 to 15 at%. Weak ferromagnetic Mn3+-Mn4+ interactions created by the substitution of Mn3+ by Cu2+, are visible through the coercive field and spontaneous magnetization but do not modify the overall magnetic frustration. Presence of Mn3+-Mn4+ pairs leads to an increase of the electrical conductivity due to thermally-activated small-polaron hopping mechanisms. Results show that local ferromagnetic interactions can coexist within the frustrated state in the hexagonal polar structure. 相似文献
17.
B.J. Ruck F. Natali N.O.V. Plank Binh Do Le M. Azeem Maha Alfheid C. Meyer H.J. Trodahl 《Physica B: Condensed Matter》2012,407(15):2954-2956
The rare-earth nitrides are ferromagnetic semiconductors with promise for spintronic devices. Their most common dopants are nitrogen vacancies (VN), with a small enough energy of formation that they exist at of order 1% in epitaxial films. Here we report preliminary investigations of their effect on the magnetic states of two of them in the series, GdN and EuN. In the former we find an enhanced Curie temperature at very high VN concentration, and the Eu2+ ions associated with VN in the latter show strong exchange with their Eu3+ neighbours that might form the basis of a diluted magnetic semiconductor. 相似文献
18.
We study long-time limit behavior of the solution of atom's master equation, for the first time we derive that the probability of the atom being in the α-th (α =j+1-jz, j is the angular momentum quantum number, jz is the z-component of angular momentum) state is {(1-K/G)/[1-(K/G)2j+1]}(K/G)α-1 as t→+∞, which coincides with the fact that when K/G > 1, the larger the α is, the larger probability of the atom being in the α-th state (the lower excited state). We also consider the case for some possible generalizations of the atomic master equation. 相似文献
19.
Jean-Francis Marucco Bertrand Poumellec Jacques Gautron Philippe Lemasson 《Journal of Physics and Chemistry of Solids》1985,46(6):709-717
By means of thermogravimetric measurements, it has been possible to obtain information on the nature of the intrinsic and extrinsic defects of TiO2, NbO2 and solid solutions NbyTi1?yO2±x Pure TiO2 is an oxygen-deficient oxide The main defects are oxygen vacancies, doubly ionized V..o or singly ionized V.o, and interstitial titanium Ti3i NbO2 is a metal-deficient oxide The main defects are neutral niobium vacancies. The solid solutions NbyTi1?yO2±x may be divided into two groups If y > 0 04, the behavior is analogous to that of NbO2; with the same defects, but the width of the homogeneity range decreases with the titanium content and Nb0 04Ti0 96O2 is a stoichiometnc oxide If y < 004, the oxides are both metal deficient and oxygen deficient according to the oxygen partial pressure. We have particularly studied the solution Ti0 995Nb0 005O2 In the oxygen-deficient domain, the main defects are assumed to be neutral or singly ionized oxygen vacancies In the metal-deficient domain, the main defects are metal vacancies V4Ti From these results we have deduced the nature of intrinsic defects in TiO2 to be Schottky defects: 2V..O + V4T1. 相似文献
20.
Magnetization and57Fe Mössbauer measurements were carried out on RFe12–x
V
x
N
y
compounds (R=Y and Nd,x=1.7 and 2.2) and the effects of nitrogen and vanadium atoms on the57Fe hyperfine fields at the different iron crystallographic sites were investigated. The hyperfine field decreases with increasing number of vanadium neighbour atoms at all the iron sites. The hyperfine field is strongly enhanced in the nitrogen composition withy>1 where the compound tends to transform into an amorphous-like solid. The iron moment deduced from the hyperfine field increases more upon nitrogenation for the 8i-site than for the other sites, and exceeds the moment of bcc iron. 相似文献