Spin configurations and spin reorientations in pure and impurity doped Fe3BO6

The spin configurations of Fe₃BO₆ above and below the spin reorientation temperature are analysed by magnetic measurements and a symmetry consideration. The effects of dopants on the magnetic properties are investigated. The dopants induces a different spin configuration and spin reorientation from the pure Fe₃BO₆.     

Anomalies in low-temperature lattice parameters of ErFeO3 and ErAlO3 single crystals: correlation with magnetic properties

The paper presents the results of an experimental study of thermal expansion of isostructural orthorhombic ErFeO₃ and ErAlO₃ single crystals. Changes of lattice parameters have been investigated by X-ray measurements in the 10-300 K temperature range. Above ∼150 K, experimental results correspond well to the phonon mechanism. At low temperatures distinct anisotropic anomalies were observed in both compounds; and a correlation with the magnetic properties of the relevant ions is noted.     

Pr掺杂DyFeO3体系的自旋重取向相变、晶格畸变与Raman光谱研究

利用固相反应法制备了Dy_1-xPr_xFeO₃系列化合物. X射线粉末衍射晶体结构分析表明, 随着Pr掺杂量x的增加, 样品晶胞体积逐渐增大, 晶格畸变减弱. Raman光谱测量表明稀土离子有效质量[m_eff=xm_Pr+(1-x)m_Dy] 与晶格结构的变化共同导致该体系Raman光谱的变化. 随Pr掺杂量的增加, 波数小于200 cm^-1的振动模式基本保持不变, 而波数大于200 cm^-1的振动模式(除420 cm^-1处的B_3u模式外)向低频移动. 磁测量结果表明, 由Dzyaloshinsky-Moriya 相互作用导致的宏观磁性随Pr掺杂量增加逐渐减弱. 稀土离子与铁离子磁晶格的耦合作用以及晶格结构畸变的变化共同导致该体系自旋重取向相变温度在一定的掺杂量 (x=0.3)前后先升高后降低. 关键词： 稀土铁氧体 自旋重取向 晶体结构 Raman光谱     

Non-universality in Z3 symmetric spin systems

The critical exponent ν of the mass gap is calculated for a one-dimensional, Z₃ symmetric quantum chain. Using the strong coupling expansion and finite-size scaling it is shown that ν varies continuously from $\text{5}\text{6}\text{to}\text{1}$.     

Visual investigation of the intermediate state in the region of metamagnetic phase transition in ErFeO3

We carried out the first observation of the intermediate state (IS) in the region of metamagnetic phase transition (MPT) in ErFeO₃: an external magnetic field H∥c (H=0–4 kOe), the temperature range 2.15–1.6 K. The ranges of the IS existence and the domain structure (DS) features were determined. Likely mechanisms of the IS thermodynamic stabilization and conditions for its visualization in ErFeO₃-plates with various crystallographic orientations were analyzed. The thermodynamic model of IS was offered: the intermediate state was stabilized by the mechanical stress that accompanies MPT. Excellent agreement with experiment was achieved.     

Proton spin lattice relaxation in single crystal of NaH3(SeO3)2

Proton spin lattice relaxation time in NaH₃(SeO₃)₂ was measured at temperatures 300-77 K at a frequency of 8.01 MHz. Except near the temperatures of the ferroelectric transitions at 196 and 100 K the relaxation rate is governed by paramagnetic impurities, and the formula derived by Blumberg for diffusion-limited case is applicable. A logarithmic divergence above 196 K is related to the anomaly of the dielectric constant in the same temperature range.     

Low-temperature absorption contour of the ν3 band of SF6

A band contour analysis is carried out for the ν₃ absorption in SF₆. Values of ΔB = ? (1.0 ? 1.5) × 10^?4cm^?1, ζ₃ = 0.701, and ν₀ = 948.2cm^?1 are found. Tentative assignments are given for the SF₆ rotational states which are pumped by the P(14) through P(22) lines of the CO₂ laser.     

Low-temperature high-resolution VUV spectroscopy of Ce doped LiYF4, LiLuF4 and LuF3 crystals

For LiYF₄:Ce³⁺, LiLuF₄:Ce³⁺ and LuF₃:Ce³⁺ crystals UV/visible emission and time-resolved VUV/UV excitation spectra were recorded at liquid helium temperature with spectral resolution of 0.1 nm for excitation spectra and better than 0.3 nm for emission spectra. Well resolved fine structures due to zero-phonon lines were clearly observed in both excitation and emission spectra for LiYF₄:Ce³⁺ and LiLuF₄:Ce³⁺. For LuF₃:Ce³⁺ crystal no fine structure was detected in the spectra even at the highest spectral resolution. Under the host excitation, the fine structure for high-energy emission band of Ce³⁺ (5d-²F_5/2) in LiLuF₄:Ce³⁺ becomes well pronounced because of weaker reabsorption effect, as compared to Ce³⁺ 4f-5d absorption, due to small penetration depth for exciting radiation. As a result the crystal-field splitting for ²F_7/2 and ²F_5/2 levels of Ce³⁺ in LiLuF₄ crystal was measured. First observation of zero-phonon lines at ∼81,550 and ∼82,900 cm⁻¹ as well as vibronic side bands due to interconfigurational 4f¹⁴-4f¹³5d transitions in Lu³⁺ is reported for excitation spectrum of LiLuF₄:Ce³⁺.     

Antiferromagnetic order and spin glass behavior in Dy2CuIn3

The magnetic properties of the intermetallic compound Dy₂CuIn₃ have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T_N=19.5 K and an additional frequency dependent transition at T_ds∼9 K. Neutron diffraction studies confirm the ordered transition at 19.5±1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment μ=2.63(4)μ_B/Dy³⁺ parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions.     

Impurity-induced magnetic order in the mixture of two spin gap systems (CH3)2CHNH3CuCl3 and (CH3)2CHNH3CuBr3

The ground state of the solid solution of the two spin gap systems (CH₃)₂CHNH₃CuCl₃ and (CH₃)₂CHNH₃CuBr₃ has been investigated by ¹H NMR. The existence of a magnetic ordering in the sample with the Cl-content x=0.85 was clearly demonstrated by a drastic splitting in a resonance line at low temperatures below T_N=13.5 K. The observed NMR spectra in the ordered state was qualitatively consistent with the simple antiferromagnetic state.     

Reentrant spin glass behaviour in Nd0.84K0.12MnO3

Polycrystalline Nd_0.84K_0.12MnO₃ was prepared in single phase form with Pbnm space group. The magnetic properties are studied from magnetization, linear and non-linear susceptibility, and thermoremanent magnetization measurements. The sample exhibits paramagnetic to ferromagnetic transition followed by low temperature spin glass like transition. From frequency variation of ac susceptibility measurements, the spin glass transition temperature is found to be 97.6±0.1 K with critical exponents zυ=1.13±0.06. The critical exponent γ corresponding to spin glass transition has been determined from the third harmonic susceptibility analysis and it is found to be 3.09±0.05. The effective number of spins blocked under frustration and their correlation length are determined from the analysis of thermoremanent magnetization.     

Electron spin resonance and optical identification of Fe4+-V0 in SrTiO3

The electron spin resonance of the minority defect Fe⁴⁺-V₀ has been observed in SrTiO₃. It is the first pair center identified with a two-fold positive charge with respect to the lattice. For Fe⁴⁺ it occurs in the unusual high spin S = 2 state. Optically-induced conversion to the neighbor Fe³⁺-V₀ charge state served to identify the acceptor transfer bands, showing the potentiality of the conversion-rate method.     

掺铌SrTiO_3中的逆自旋霍尔效应

采用磁控溅射法在未掺杂和掺杂的SrTiO_3基片上沉积了NiFe薄膜,通过翻转测试法分离出掺杂样品中的自旋整流电压和逆自旋霍尔电压.研究结果表明:在未掺杂的SrTiO_3基片中,翻转前后测试的电压曲线基本一致,为NiFe薄膜自旋整流效应产生的电压.对于掺Nb浓度x为0.028, 0.05, 0.1, 0.15, 0.2的SrTiO_3基片,分离出的逆自旋霍尔电压随掺杂浓度增加而减小,在掺杂浓度为0.15和0.2的样品中没有探测到明显的逆自旋霍尔电压.本文的结果表明,在SrTiO_3中掺入强自旋轨道耦合的杂质,通过掺杂浓度可以实现对SrTiO_3中逆自旋霍尔效应的调控,这类可调控的自旋相关研究为自旋电子器件的研究和开发提供了更多的可能性,具有很大的潜在应用价值.     

Electron spin resonance investigation of the structural phase transitions in Alurea6(ClO4)3 and Ga urea6(ClO4)3

Second order structural phase transitions in Alur₆(ClO₄)₃ and Gaur₆(ClO₄)₃ with T_c ～ 300 K are studied by means of ESR on single crystals doped with the analogous Cr(III) compound. The transitions are antiferrodistortive and of the displacive type, the displacements resulting from the condensation of a X₂ mode $\text{(k = (0}\text{1}\text{2}\text{1}\text{2}\text{))}$ of the ClO₄ ions. The ESR parameters have the same temperature dependence as the order parameters and can be described by D and E～φ～. The space group describing the structure changes from S₆² to S₂¹, and the number of domains is multiplied by three. Above 300 K the crystals already consist of two domains, resulting from a ferrodistortive phase transition D_3d⁶ → S₆². The actual transition temperature of the latter phase transition lies at some temperature above the decomposition temperature of the crystals.     

NMR observation of the spin structure and field induced spin reorientation in YFeO3

For the first time the ⁵⁷Fe NMR spectrum of the nuclei in the domains of a YFeO₃ single crystal has been observed. The splitting of the lines by an external magnetic field allows a very exact determination of the spin orientation of the four Fe sublattices. The ferro- and antiferromagnetic canting angles in zero field are φ = 12.3 mrad and ψ = 14.0 mrad, respectively. The field-induced spin reorientation can be described using the model of antisymmetric exchange interaction including second- and fourth-order anisotropy constants.     

Electron spin resonance of diluted solid solutions of MnO2 in Y2O3

Electron spin resonance spectra of Mn²⁺ in diluted solid solutions of MnO₂ in Y₂O₃ have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn²⁺ ions in sites with two different symmetries were observed, as well as Mn²⁺ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn²⁺ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C₂ symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn²⁺ ions of 0.53 nm, of the same order as that of Mn²⁺ ions in CaO.     

The ν3 and 2ν3 bands of SO3, SO3, SO3, and SO3

This sixth of a series of publications on the high-resolution rotation-vibration spectra of sulfur trioxide reports the results of a systematic study of the ν₃ and 2ν₃ infrared bands of the four symmetric top isotopomers ³²S¹⁶O₃, ³²S¹⁸O₃, ³⁴S¹⁶O₃, and ³⁴S¹⁸O₃. An internal coupling between the l=0(A₁^′) and l=2(E^′) levels of the 2ν₃ states was observed. This small perturbation results in a level crossing between |k−l|=9 and 12, in consequence of which the band origins of the A₁^′,l=0 “ghost” states could be determined to a high degree of accuracy. Ground and upper state rotational constants as well as vibrational anharmonicity constants are reported. The constants for the center-of-mass substituted species ³²S¹⁶O₃ and ³⁴S¹⁶O₃ vary only slightly, as do the constants for the ³²S¹⁸O₃, ³⁴S¹⁸O₃ pair. The S-O bond lengths for the vibrational ground states of the species ³²S¹⁶O₃, ³⁴S¹⁶O₃, ³²S¹⁸O₃, and ³⁴S¹⁸O₃ are, respectively, 141.981 99(1), 141.979 38(6), 141.972 78(8), and 141.969 93(8) pm, where the uncertainties, given in parentheses, are two standard deviations and refer to the last digits of the associated quantity.     

The spin glass-like behaviour of the glassy (Sb2S3)x(SbI3)yFez

Low field magnetic susceptibility of a glassy semiconductor (Sb₂S₃)_x(SbI₃)_yFe_z reveals a spin glass-like behaviour in spite of the sample not being metallic. The critical temperature is observed to depend on the concentration of the iron atoms (T_M = 0.179z^0.76).     

Ab-initio study of competing magnetic configurations in cubic BiFeO3 alloys

Using ab-initio calculations, we study the properties of the multiferroic BiFeO₃ compounds in the perfect cubic perovskite lattice structure. We show that the appearance of magnetism is energetically favorable. Except the ferromagnetic structure, there are three possible antiferromagnetic arrangements, which are close in energy, and for large values of the lattice constant a G-type antiferromagnetism is the most stable magnetic order. Fe atoms are responsible for the spin magnetic moments while the values of the induced spin moments at the other sites depend strongly on the local environment of the atoms. There is a significant charge transfer from the Fe and Bi atoms towards the p-states of O atoms.