Phenomenological analysis of the linear magnetic birefringence in dysprosium iron garnet

Experimental data on linear magnetic birefringence (LMB), previously reported at 1.15 μm wavelength in the 4.2-300 K temperature range and with an applied field up to 20 kOe, in dysprosium iron garnet (DyIG) are analyzed in terms of electric dipole transition within the three magnetic sublattices. Assuming that the garnet symmetry is cubic and that the contribution of the Fe³⁺ ions to LMB is the same as yttrium iron garnet (YIG), the 2nd order magneto-optical (MO) coefficient (Γ₂) of the Dy³⁺ ions is deduced. In the spontaneous state, Γ₂ is linear temperature dependent as previously found for the 1st order (MO) coefficient. It is shown that Γ₂ must be field dependent to explain the evolution of the LMB.     

HREM of the [111] surfaces of iron oxide nanoparticles

Mixed phase Fe3O4-gamma-Fe2O3 (magnetite-maghemite) iron oxide nanoparticles have been fabricated by colloidal routes. HRTEM/HRSTEM images of the nanoparticles show the presence of [111] facets that terminate with enhanced contrast, which is shown to be caused by the presence of additional cations at the edges of the nanoparticles. HRTEM images were taken on a FEI CM200 FEGTEM, a JEOL 3100 with a LaB6 source, and a double aberration corrected JEOL-JEM 2200FS FEGTEM. The enhanced contrast effect was observed on the [111] surface atomic layers resolved using each machine. HRSTEM images, taken on an aberration corrected STEM, resolved enhanced contrast at specific surface sites. Exit wave reconstruction was also carried out on focal series taken on a double aberration corrected JEOL-JEM 2200FS and showed similar highly resolved enhanced contrast at specific surface cation sites. It is apparent that additional cations are occupying the [111] terminating layers of these nanoparticle surfaces. The use of different microscopes and techniques in this paper provides strong evidence that the enhanced contrast is a real effect and not an effect caused by microscope aberrations.     

Domain structure of a thin single-crystal plate of terbium iron garnet near the magnetic compensation point

The domain structure of a thin single-crystal plate of the iron garnet Tb₃Fe₅O₁₂ has been investigated using the magneto-optical method in the temperature range near the magnetic compensation point of this ferrimagnet T _c = 248.6 K. It has been shown that, when the temperature of the sample approaches the magnetic compensation point, the domain width significantly increases, but remains finite at T = T _c . The magnetic H-T phase diagram, which determines the boundary between the multidomain and domain-free (uniformly magnetized) states of the sample, has been constructed using the data on visual observations of the transformation of the domain structure with variations in the temperature and external magnetic field. The results obtained have been interpreted in terms of the thermodynamic theory of stability of different magnetic phases of a two-sublattice cubic ferrimagnet near T _c .     

Electron energy loss study of TiC [111]

The electron energy loss (EEL) spectra of TiC (111) were measured over a wide range of electron primary energies. The electron energy losses below 16 eV were analyzed using the theoretical band calculations of Price and Cooper [11]. The volume and surface plasma excitations were identified from their electron primary energy dependence. Energy losses due to core electrons autoinization effects were identified above 35 eV. We observed a difference in the electronic structure of the surface vs the bulk of TiC. The temperature dependence of the EEL spectra was studied between 300 to 1250 K. The reaction of the TiC surface with ethylene and oxygen was also investigated. The ethylene bonding to the TiC surface was found to be very weak. There is evidence of the formation of surface defects on the TiC (111) surface at high temperatures.     

An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field

The superexchange interaction on a magnetic ion may be represented by an effective field H_m = $\lambda$M in some paramagnetic materials, here λ is the coefficient of effective field and M = $\chi$H_e with $\chi$ being the magnetic susceptibility and H_e being the applied field. The variation of the equivalent $\lambda_{\chi}$with the dynamic applied field is given and the crystal field-splitting levels of the excited configuration 4f⁷5d¹ of the Tb³⁺ ion are calculated in the Tb₃Ga₅O₁₂. By means of the effective field H_m and the applied field H_e, the Faraday rotation of Tb₃Ga₅O₁₂ at 6 K and 41 K, under the high magnetic field and at 0.63 μm wavelength, are presented. Our calculated results are in agreement with the experimental data.     

第一性原理研究[111]晶向硅纳米线电子结构,光学性质与压阻特性的应变效应

基于密度泛函理论体系下的广义梯度近似(GGA),利用第一性原理方法计算研究了单轴应变对[111]晶向硅纳米线的电子结构、光学性质以及压阻性质的影响.能带结构和光学性质的结果表明:压应变导致硅纳米线的带隙明显线性减小,且使其由直隙半导体转变为间隙半导体,而施加拉应变后硅纳米线仍为直隙半导体材料,但是带隙略有减小,且价带顶附近的能带线产生了较为复杂的变化.由于能带的应变效应导致其光学性质也相应发生了较大改变:拉应变使硅纳米线的介电峰出现宽化现象,低能区内的光吸收增强,静态折射率和反射率峰值增大,而压应变的效果则相反.结合能带结构与压阻系数计算模型得到的压阻特性结果表明:随着压应变的增加压阻系数单调减小,这主要归因于空穴浓度随压应变显著变化引起的;而拉应变作用时,压阻系数呈现波动趋势,这主要是由于空穴有效传输质量的增加程度和载流子浓度的增加程度不同而相互竞争导致的.上述计算结果表明,设计基于硅纳米线的光电和力电器件时,需考虑其应变效应.     

第一性原理研究[111]晶向硅纳米线电子结构，光学性质与压阻特性的应变效应

基于密度泛函理论体系下的广义梯度近似（GGA）,利用第一性原理方法计算研究了单轴应变对[111]晶向硅纳米线的电子结构、光学性质以及压阻性质的影响．能带结构和光学性质的结果表明：压应变导致硅纳米线的带隙明显线性减小,且使其由直隙半导体转变为间隙半导体,而施加拉应变后硅纳米线仍为直隙半导体材料,但是带隙略有减小,且价带顶附近的能带线产生了较为复杂的变化．由于能带的应变效应导致其光学性质也相应发生了较大改变：拉应变使硅纳米线的介电峰出现宽化现象,低能区内的光吸收增强,静态折射率和反射率峰值增大,而压应变的效果则相反．结合能带结构与压阻系数计算模型得到的压阻特性结果表明：随着压应变的增加压阻系数单调减小,这主要归因于空穴浓度随压应变显著变化引起的;而拉应变作用时,压阻系数呈现波动趋势,这主要是由于空穴有效传输质量的增加程度和载流子浓度的增加程度不同而相互竞争导致的．上述计算结果表明,设计基于硅纳米线的光电和力电器件时,需考虑其应变效应．     

Effect of Bi-substitution on the dielectric properties of polycrystalline yttrium iron garnet

The effect of Bi-substitution on the dielectric properties of yttrium iron garnet (YIG) was studied in this paper. The Bi-substituted YIG (YIG:Bi) polycrystalline samples, having composition of Y_3−xBi_xFe₅O₁₂, were prepared by the solid-state reaction method. x varied from 0 to 1.2. The phase formation and microstructure were performed by X-ray diffraction and scanning electron microscopy, respectively. Ions valency was identified by X-ray photoelectron spectroscopy. The impedance analyzers are used to measure the frequency dependence and the temperature dependence of relative dielectric constant (_r) and loss tangent (tan δ). The experimental results show that the Bi-substitution lowers the phase formation and sintering temperature. Electronic carrier concentration drops dramatically due to limitation of ferric valency variation. Hence, _r and tan δ decrease with addition of Bi. Dispersion characteristic indicates non-Debye-type dispersion. A maximum of _r appears as the temperature rises.     

Effect of reversible adsorption on the magnetic properties of iron garnet films

The reversible change in the domain structure and the magnetic domain width in bismuth-containing iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption-desorption processes occurring between methyl alcohol molecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects.     

A comparison of the magnetic anisotropy of [001] and [111] oriented Co/Pd Multilayers

Superlattices of [001]_fcc Co/Pd with varying Co thicknesses from one to eight atomic layers per modulation period were epitaxially grown on NaCl by vapour deposition in UHV. Transmission electron diffraction indicates lattice coherence between the Co and the Pd layers for Co thicknesses up to six atomic layers. If deposited at a substrate temperatureT _s=50°C, only the superlattices containing Ci-monolayers show perpendicular magnetization. By raisingT _s to 200°C, the perpendicular anisotropy for Co monolayers is increased, and is also observed for Co bilayers. We suggest that this is due tolayer smoothening, which increases Néel's interface anisotropy. For more than 6 atomic layers of Co a loss of coherence is observed atT _s=50°C, accompanied by a structure transformation to hcp Co with a (0001)_Co(111)_Pd orientation.Non-epitaxial polycrystalline [111]-multilayers have a different anisotropy versus thickness behaviour. For such multilayers the range of Co thicknesses giving perpendicular magnetization is extended from 8 Å up to 12 Å atT _s=200°C. The different behaviour of the single crystal [001] films is caused by a strong volume contribution to the anisotropy, which favours in-plane magnetization, opposing the perpendicular interface anisotropy. This easy-plane term is attributed to magneto-elastic anisotropy due to stretching of the Co layers, via a positive magnetostriction.     

Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Polar Kerr rotation spectra in yttrium iron garnet and lithium ferrite: A comparative study

Polar Kerr rotation (PKR) spectra in the range 2.0–5.7 eV at 295 K of lithium ferrite and yttrium iron garnet (YIG) single crystals are reported. The spectra show more details and cover a more extended energy region than those published so far. The interpretation of the spectra is based on the assumptions that 1) PKR is an odd function of the sublattice magnetic moments 2) the origin of PKR in both compounds is of similar nature, the differences due to the different crystal structures (garnet and spinel) being less important. The calculated PKR sublattice components show some similarities in their energy dependences, the magnitude of the tetrahedral sublattice component being higher than that of the octahedral one. The components were used in the calculation of the PKR spectra in diamagnetically substituted yttrium iron garnet (J. Appl. Phys.49, 2212, 1978). The results correctly predict the trends observed experimentally.     

Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Electronic band structure of Cu3Au: An angle-resolved photoemission study along the [111]-direction

High-resolution normal photoemission (ARPE) spectra have been recorded for Cu₃Au(111) with the use of polarized synchrotron and rare-gas resonance radiation in the photon energy range from 9 to 27 eV. It is for the first time that dispersions of the gold-like bands have been found experimentally. Using a fully relativistic layer-KKR photoemission formalism, occupied and unoccupied bands as well as one-step-model photoemission spectra have been calculated. The comparison of calculated spectra with experimental ones and the observation of direct-transition resonances upon photon energy near the Brillouin zone-center reveal a shift of the unoccupied ground-state bands by about +2.5 eV (self-energy shift). The direct-transition structures in the experimental spectra have been exploited to determine the dispersions of the occupied bands along the [111] direction (A line in k space). In order to determine the wave vector of the experimental direct transitions we used as final state that calculated unoccupied band along [111], which also exists in pure copper and gold up to about 20 eV above the Fermi energy (“unfolded” band structure), shifted by + 2.5 eV. The experimental occupied bands with Cu character are in very good agreement with theory after shifting the latter by about 0.3 eV to lower energy, whereas somewhat bigger discrepancies exist for the gold-like bands.     

Topological properties of Sb(111) surface: A first-principles study

First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in (111) orientation. By considering the spin-orbit interaction, for stoichiometric surface, the topological states keep robust for six-bilayer case, and can be recovered in the three-bilayer film, which are guaranteed by time-reversal symmetry and inverse symmetry. For reduced surface doped by non-magnetic Bi or magnetic Mn atom, localized three-fold symmetric features can be identified. Moreover, band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom, while can be eliminated by adsorbed or substitutional magnetic Mn atom.     

The influence of NiO addition on the magnetic properties of polycrystalline yttrium iron garnet

The influence of NiO addition on the magnetic properties of polycrystalline Y₃Fe₅O₁₂ is studied for the saturation magnetization, Curie temperature, initial magnetic permeability and ferromagnetic resonance line width. Dependence of saturation magnetization on NiO addition suggest that Ni²⁺ ions enter octahedral sites of the garnet lattice. Real part of the complex initial permeability versus temperature curves reveal the single phase for samples with NiO content. The absence of any additional peak in these curves and the invariance of Curie temperature suggest that NiO addition cannot alter the magneto-crystalline anisotropy of the material. Variations of initial permeability with NiO content are due to change of saturation magnetization and grain size of the materials. The ferromagnetic resonance line width varies linearly with the porosity of samples with NiO showing no anisotropy contribution in it.     

Effect of treatment in a corona discharge on the surface properties of iron garnet films

Experimental investigations of the influence of a corona discharge on magnetic properties and domain structure of iron garnet films are conducted. We show that changes in the physical properties of iron garnet films due to a corona discharge result from the injection of negative oxygen ions and the formation of an electret state.     

Magneto-optical properties of the iron garnet Tb3Fe5O12 near the magnetic compensation temperature

The magneto-optical susceptibility and magnetic hysteresis loops of the Faraday effect, which accompany the technical magnetization of the iron garnet Tb₃Fe₅O₁₂, have been investigated experimentally in the temperature region near the magnetic compensation point of this ferrimagnet T _c = 249 K. It has been found that, during the technical magnetization as the temperature approaches the magnetic compensation point T _c , the velocity of domain walls increases, whereas the magneto-optical susceptibility has local maxima to the right and to the left from T _c . Mentioned features of magneto-optical properties of the iron garnet Tb₃Fe₅O₁₂ are associated with the resonance natural frequency of the domain wall oscillations in the crystal with the frequency of the alternating magnetic field. It has been shown that the used theoretical model of the magnetic resonance of domain walls makes it possible to consistently describe (at the qualitative level) the revealed regularities of the variation of the Faraday effect in the iron garnet Tb₃Fe₅O₁₂ near T _c .