High-temperature Raman spectra of KDP:Ni crystal

High-temperature Raman scattering measurements of KDP doped with Ni (1% weight) were performed over the spectral range 50–1200 cm^?1. The X-ray powder diffraction patterns taken at room temperature and analyzed by Rietveld refinement showed that doped samples of KDP:Ni have the same tetragonal structure of a pure KDP crystal, but with a contraction of the crystalline cell. The behavior of the high-temperature Raman spectra indicate that two phase transitions occur, one at 413 K and another one at 443 K. These phase transitions occur at temperatures below the thermal dehydratation point, 488 K. DTA and TGA measurements reveals that KDP:Ni and pure KDP have the same thermal dehydratation temperature.     

Effect of an organic dye on the ferroelectric phase transition in KH2PO4 (KDP)

This paper reports on the first measurement of the dielectric permittivity and heat capacity of a KDP crystal doped by Chicago Sky Blue organic dye within a temperature interval including the ferroelectric phase transition at T _c =122 K. Similar measurements were made on a pure KDP crystal under the same conditions for the sake of comparison. The heat capacities of the pure and doped crystals were shown to differ substantially within an interval 1 K wide in the vicinity of T _c , where an anomaly in the heat capacity of the doped crystal was observed to wash out without producing any change in the temperature position of its maximum. The doping reduces the permittivity in the polar phase markedly. The observed effects are associated with the influence of nonisomorphic defects on the ferroelectric phase transition in a piezoelectric crystal.     

Vibrational spectroscopy of indium-doped Pb0.9Mn0.1Te alloy

Raman scattering and far-infrared reflection spectra of 0.5 at.% In doped Pb_0.9Mn_0.1Te single crystal at temperatures between 10 and 300K are presented. The infrared spectra have been fitted using a modified plasmon-phonon interaction model with an additional oscillator (at about 122 cm^?1) representing a local In-impurity mode. Phonons in this mixed crystal exhibit intermediate mode behavior. The plasma frequency decreases on cooling from 300 to 25K and increases sharply between 20 and 10 K. The results of galvanomagnetic measurements are also presented.     

CW one-micron (4F3/2-4I11/2) laser oscillation of Nd3+ ions in the melilite-type crystal Ca2MgSi2O7:Nd3+(Na+) at its incommensurate–commensurate phase transition

The spectroscopic and stimulated-emission (⁴F_3/2→⁴I_11/2) properties of the novel melilite-type laser crystal Ca₂MgSi₂O₇:Nd³⁺(Na⁺) were studied in a temperature range that covers its incommensurate–commensurate (IC↔N) phase transition. The phase transition temperatures of both undoped Ca₂MgSi₂O₇ and the doped crystal were ascertained at 346.6 K (undoped) and 341.3 K (doped) by means of differential scanning calorimetry (DSC). The temperature-dependent spectroscopic and laser experiments showed a significant decrease in CW output power and a strong distortion of the generated lasing beam in the region of the phase transition. The observed crystal field disorder of Nd³⁺ lasants in Ca₂MgSi₂O₇:Nd³⁺(Na⁺) is dominantly due to occupation of the position of Ca²⁺ by cations of different valency, while the influence of incommensurability is of minor importance.     

A variable temperature EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 170 GHz: zero-field splitting parameter and its absolute sign

EPR measurements have been carried out on a single crystal of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) at 170-GHz in the temperature range of 312-4.2K. The spectra have been analyzed (i) to estimate the spin-Hamiltonian parameters; (ii) to study the temperature variation of the zero-field splitting (ZFS) parameter; (iii) to confirm the negative absolute sign of the ZFS parameter unequivocally from the temperature-dependent relative intensities of hyperfine sextets at temperatures below 10K; and (iv) to detect the occurrence of a structural phase transition at 4.35K from the change in the structure of the EPR lines with temperature below 10K.     

Suppression of electron correlations in the superconducting alloys of Rh17−xIrxS15

We have studied the effect of Iridium doping (Rh_17?xIr_xS₁₅) in the rhodium sites of the strongly correlated superconductor Rh₁₇S₁₅. Even at low levels of doping (x = 1 and 2) we see a drastic change in the superconducting properties as compared to those of the undoped system. We deduce that there is a reduction in the density of states at the Fermi level from reduced Pauli susceptibility and Sommerfeld coefficient in the doped samples. Moreover, the second magnetization peak in the isothermal magnetization scan (‘fishtail’) which was very prominent in the magnetization data of the undoped crystal is suppressed in the doped samples. The temperature dependence of resistivity of the doped crystals show a remarkably different behavior from that of the undoped crystal with the appearance of a minima at lower temperatures, the position of which is fairly constant at different fields. Our data supports the notion that Iridium, which is a bigger atom than rhodium expands the lattice thereby, reduces the electron correlations that existed due to the interaction between closer lying rhodium atoms in the undoped system.     

DyNi2Mn—magnetisation and M?ssbauer spectroscopy

The physical properties of DyNi₂Mn doped with ⁵⁷Fe have been investigated by X-ray diffraction, magnetisation (10–300?K) and ⁵⁷Fe M?ssbauer spectroscopy measurements (5–300?K). DyNi₂Mn(⁵⁷Fe) crystallizes in the MgCu₂-type cubic structure (Fd^??3m space group). The ordering temperature is found to be T_C?=?99(2) K, much higher than those of DyNi₂ (～22?K) and DyMn₂ (～35?K). Analyses of isothermal M–H curves and the related Arrott plots confirm that the magnetic phase transition at T_C is second order. The magnetic entropy change around T_C is 4.0?J/kg?K for a magnetic field change of 0?T to 5?T. The spectra above T_C exhibit features consistent with quadrupolar effects while below T_C the spectra exhibit magnetic hyperfine splitting. The Debye temperature for DyNi₂Mn has been determined as θ_D?=?200(20) K from a fit to the variable temperature isomer shift IS(T).     

Structural transformations in a single‐crystal Rb2NaYF6: Raman scattering study

This paper reports Raman spectroscopy investigation of phase transitions in Rb₂NaYF₆ crystal. The experimental spectra were compared with the calculated one. The spectra were obtained in temperature range from 8 to 300 K. The Raman spectra shows anomalous temperature‐dependent behavior at T₁ = 154 and T₂ = 122 K. Soft mode restoration has been found, which allows us to attribute first transition at 154 K to displacive type. Detailed analysis temperature dependencies of the line positions and widths have been performed. We found no effects of possible lattice disorder anywhere, except narrow (about 20 K) range above the T₁ temperature. The Raman spectra of Rb₂NaYF₆ crystal have been obtained and analyzed under hydrostatic pressure up to 4.33 GPa (at T = 295 K). The high pressure experiment up to 4.33 GPa did not disclose any effects associated with phase transitions. The lattice vibration spectra were calculated up to 10 GPa. The calculation has been demonstrated that the Rb₂NaYF₆ does not undergo high pressure phase transition. Copyright © 2013 John Wiley & Sons, Ltd.     

EPR of Mn2+ doped in Zn(BF4)26H2O

EPR of Mn²⁺ doped (∼ 1%) in single crystal of zinc fluoroborate hexahydrate has been studied between 94 and 353 K. Angular variation study of the spectra indicated that the crystal field distortion has a trigonal symmetry along the crystallographic c-axis. The D distortion parameter has two linear regions in its thermal variation. It varies above 200 K as D = (149 + 0.107T)G and below 150 K as xzD = (127 + 0.228T)G. A “knee”-like curve links these two linear regions confirming an anomaly observed in a previous work at 181 K due to a phase transition. Other spin Hamiltonian parameters are g = 2.000 ± 0.001, a = (8.9 ± 1.5)G, A = (97.9 ± 0.9)G and B = (97.0 ± 0.9)G. They are constant with temperature.     

High spin state of Mn in an ideal monolayer on Ag(001)

We studied the magnetic properties of ultra-thin Mn films deposited on Ag (001) held at 80 K with soft X-ray absorption and magnetic circular dichroism. The observed shape and branching ratio of the Mn 2p absorption edge as a function of Mn coverage demonstrate that, up to , the Mn adopts a stable high spin state similar to the Mn atom Hund's rule ⁶ S _5/2 ground state. Above this coverage a rapid transition from localized high spin to itinerant low spin behavior of the Mn 3d electrons is evidenced. Magnetic circular dichroism shows no sign of long range ferromagnetic order in these films at 80 K. The data, first confirm the large atomic-like local magnetic moment, and second are in line with the in-plane antiferromagnetic order, reported recently (Phys. Rev. B 57, 1141 (1998)), for Mn in the nearly ideal on-top Mn monolayer formed by 0.9 ML deposited at 80 K. Received: 4 May 1998     

Diffusionskonstante und charakteristische Absorption vor der Bandkante von Mn in ZnO-Kristallen

ZnO single crystals were doped with Mn and Co by diffusion. In the temperature range from 1400–1600 K the Mn and Co-diffusion-constants were determined:D _Mn=3.2 · 10^?3 exp (?2.87 eV/kT) cm² sec^?1 andD _Co=1·10exp(?3.98 eV/kT) cm² sec^?1. The Mn doped ZnO crystals show a characteristic colour due to an absorption near the intrinsic absorption edge. The corresponding absorption spectra were measured forE⊥c andE∥c. A discussion of different absorption mechanism shows that a charge-transfer transition is responsible for this absorption.     

Possible origin of room-temperature ferromagnetism in undoped GaN epilayers implanted with Mn ions

Manganese ions were implanted into unintentionally doped GaN epilayers grown by metal organic chemical vapor deposition (MOCVD). The (Ga,Mn)N and Ga_xMn_y 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 Ga_xMn_y phases play a critical role in providing holes and also contribute to increasing the ferromagnetic property.     

Mn-Mg共掺杂AlON荧光粉制备及荧光性质

采用固相反应法成功合成了一系列Mn-Mg共掺的Al₂₃O₂₇N₅荧光粉。结果显示煅烧条件和Mn的掺杂浓度对Mn-Mg共掺的AlON荧光粉的制备和发光性质都有重要影响。获得纯相AlON的温度从未掺杂的1 900 ℃下降到10% Mn和10% Mg(摩尔分数)共掺杂的1 800 ℃。晶格参数随着Mn掺杂浓度升高而增加,说明Mn进入了AlON晶格中。未掺杂和Mg单掺以及10% Mn和10% Mg共掺杂样品的发射光谱都含有一个350～600 nm之间的宽带发射。绿光发射归属于Mn的3d电子之间的传输。蓝光发射可能与杂质或Al空位相关。     

Mn和N共掺ZnO稀磁半导体薄膜的研究

使用对Zn₂N₃:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下,ZnO:Mn薄膜的铁磁性非常微弱;如果进行N离子的共掺杂,就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性,饱和离子磁矩为0.23 μ_B—0.61 μ_B.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性,也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合,这和最近的相关理论研究符合很好. 关键词： 磁性半导体 受主掺杂 空穴媒介的铁磁性     

Structural, magnetic and electronic structure studies of Mn doped TiO2 thin films

We report structural, magnetic and electronic structure study of Mn doped TiO₂ thin films grown using pulsed laser deposition method. The films were characterized using X-ray diffraction (XRD), dc magnetization, X-ray magnetic circular dichroism (XMCD) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase related to Mn metal cluster or any oxide phase of Mn. Magnetization studies reveal that both the films (3% and 5% Mn doped TiO₂) exhibit room temperature ferromagnetism and saturation magnetization increases with increase in concentration of Mn doping. The spectral features of XMCD at Mn L_3,2 edge show that Mn²⁺ ions contribute to the ferromagnetism. NEXAFS spectra measured at O K edge show a strong hybridization between Mn, Ti 3d and O 2p orbitals. NEXAFS spectra measured at Mn and Ti L_3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO₂ films.     

Synthesis and magnetic properties of Mn doped CuO nanowires

Study of diluted magnetic semiconductor nanowires is one of the important topics in materials science. By using Mn-Cu alloy as the starting material, Mn doped CuO nanowire arrays have been synthesized in air at the temperature of 550 °C. X-ray diffraction measurements and scanning electron microscopic study shows that the nanowires were grown on Cu₂O substrate. Transmission electron microscopic study shows the single crystal property of the nanowires. Magnetic measurements show ferromagnetic property in the Mn doped CuO nanowires with the critical temperature higher than 80 K.     

A study on the formation and stability of quasicrystal in Al4Mn and Al6Cr

Abstract

The condition of the formation of quasicrystal in Al₄Mn and Al₆Cr under high static pressure has been investigated for the first time. I-phase and T-phase have been observed in electron diffraction experiment. The structures of Al₄Mn quenched at about 100 K/s are different under various pressure from 0.95GPa to 4.45GPa. The phase transition from I- and T-phase to crystal phase has also been investigated.     

Synthesis and magnetic properties of Mn doped ZnO nanowires

Mn doped ZnO nanowires have been synthesized using a simple autocombustion method. The as-synthesized Mn doped ZnO nanowires were characterized by X-ray diffraction and transmission electron microscopy. An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Mn concentration. Optical absorption studies show an increment in the band gap with increasing Mn content, and also give evidence for the presence of Mn²⁺ ions in tetrahedral sites. All Zn_1−xMn_xO (0≤x≤0.25) samples are paramagnetic at room temperature. However, a large increase in the magnetization is observed below 50 K. This behavior, along with the negative value of the Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicate ferrimagnetic behavior. The origin of ferrimagnetism is likely to be either the intrinsic characteristics of the Mn doped samples, or due to some spinel-type impurity phases present in the samples that could not be detected.     

Defect-mediated ferromagnetism in ZnO:Mn nanorods

In this work, the structural, chemical and magnetic properties of ZnO:Mn nanorods were investigated. Firstly, well-aligned ZnO nanorods with their long axis parallel to the crystalline c-axis were successfully grown by the vapor phase transport technique on Si substrates coated with a ZnO buffer layer. Mn metal was then diffused into these nanorods at different temperatures in vacuum. From SEM results, ZnO:Mn nanorods were observed to have diameters of ～100 nm and lengths of 4 μm. XPS analysis showed that the Mn dopant substituted into the ZnO matrix with a valence state of +2. Magnetic measurements performed at room temperature revealed that undoped ZnO nanorods exhibit ferromagnetic behavior which may be related to oxygen vacancy defect-mediated d ⁰ ferromagnetism. ZnO:Mn samples were seen to show an excess room temperature ferromagnetism that is attributed to the presence of oxygen vacancy defects forming bound magnetic polarons involving Mn.     

Effect of regimes of cooling in a magnetic field on the magnetization of a La0.9Sr0.1MnO3 single crystal

Magnetization measurements were performed on a lanthanum manganite La_0.9Sr_0.1MnO₃ single crystal in the temperature interval 4.2–300 K and magnetic field interval 50 Oe-55 kOe in two sample cooling regimes: 1) cooling down to 4.2 K in a high (55 kOe) magnetic field, and 2) cooling in a “zero” field. It is shown that the temperature dependences of the magnetization M(T) are substantially different in these regimes. Pronounced anomalies of M(T) were observed at temperatures T*=103 K and T _c =145 K. The first anomaly is attributed to a structural transition, while the second one corresponds to a ferromagnet-paramagnet phase transition. The magnetization of a La_0.9Sr_0.1MnO₃ single crystal in the cooling regimes studied shows typical “spin-glass” behavior. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 39–43 (10 July 1998)