Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken ⁵⁷Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive ⁵⁷Mn^?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.     

57Fe Emission Mössbauer Study on Gd3Ga5O12 implanted with dilute57Mn

⁵⁷Fe emission Mössbauer spectroscopy has been applied to study the lattice location and properties of Fe in gadolinium gallium garnet Gd₃Ga₅O₁₂ (GGG) single crystals in the temperature interval 300 – 563 K within the extremely dilute (<10^?4 at.%) regime following the implantation of⁵⁷Mn (T¹_/2= 1.5 min.) at ISOLDE/CERN. These results are compared with earlier Mössbauer spectroscopy study of Fe-doped gadolinium gallium garnet Gd₃Ga₅O₁₂(GGG), with implantation fluences between 8×10¹⁵ and 6×10¹⁶ atoms cm^?2. Three Fe components are observed in the emission Mössbauer spectra: (i) high spin Fe²⁺ located at damage sites due to the implantation process, (ii) high spin Fe³⁺ at substitutional tetrahedral Ga sites, and (iii) interstitial Fe, probably due to the recoil imparted on the daughter^57?Fe nucleus in the β^? decay of⁵⁷Mn. In contrast to high fluence⁵⁷Fe implantation studies the Fe³⁺ ions are found to prefer the tetrahedral Ga site over the octahedral Ga site. No annealing stages are evident in the temperature range investigated. Despite the very low concentration, high-spin Fe³⁺ shows fast spin relaxation, presumably due to an indirect interaction between nearby gadolinium atoms.     

关於镧La_(57)的超精细结构

实验上定出的La_(57)的超精细结构常数(a(~2D_(5/2)))/(a(~2D_(3/2)))之比比由单组态的理论计算出的结果约大三倍。要想解释这个差别,一个比较常用的方法就是加入一些组态混合。我们首先考虑到在基态(6s)~2(5d)之外再加上一些(6s)(7s)(5d)的混合,并作了详细的计算,得到的结果只能对单组态的理论稍加修正,而距实验值仍相差甚远。其次又考虑到混合一些(5d)~2(6s)的态,因为这种组态能量比较低,所以混合的比例可能比较大,於是所产生的修正也比较大。经过一些简单的分析和估计,得出:要能解释实验,则所需混入(5d)~3(6s)的比例太大(约为0.36),因此我们认为虽然混入(5d)~2(6s)是可能对理论值有较大的修正,但要与实验符合还是相当困难的。     

Synchrotron Mössbauer source of57Fe radiation

A nonradioactive source of Mössbauer radiation is described for use in Mössbauer absorption and scattering spectroscopy. The radiation is generated by synchrotron Xrays in an iron borate single crystal set in diffraction conditions at the Néel temperature (75.3°C). Like a conventional Mössbauer source the new Synchrotron Mössbauer (SM) source emits singleline radiation of about natural linewidth, but in addition the emitted radiation is fully recoilless, highly directed and of pure linear polarization. An extremely high suppression of the electronic scattering is achieved. The latter circumstance allows one to perform Mössbauer experiments using pulsed synchrotron radiation in a steady state mode as in a normal Mössbauer measurement.The theory of the SM source is developed. First Mössbauer spectra obtained with the SM source are shown. Applications of the SM source are discussed.     

57Fe Mössbauer investigations of manganese-containing spinels

Cation distributions and related order-disorder phenomena in the naturally occurring Mn-spinels: iwakiite, galaxite and franklinite, have been investigated by means of⁵⁷Fe Mössbauer spectroscopy. Previous measurements on an iwakiite sample indicated the existence of Mn-rich and Mn-poor regions. This interpretation has been confirmed in this investigation by further measurements on annealed iwakiite samples. The⁵⁷Fe Mössbauer spectrum of galaxite from Bald Knob, NC, is a well-resolved quadrupole doublet and indicates the presence of a single crystallographic Fe³⁺ species. A galaxite sample from Thailand exhibited a complex spectrum of Fe²⁺ and Fe³⁺ quadrupole doublets: This sample has been misidentified and should be regarded as a member of the (Mg, Fe)(Al, Fe)₂O₄ series. The⁵⁷Fe hyperfine parameters of a rare franklinite from Längban, Sweden, are very close to those for synthetic zinc ferrite, confirming electron microprobe results of an unusually high zinc content.     

Mössbauer effect diffraction from polycrystalline57Fe

We built a Debye-Scherrer type powder diffractometer with a⁵⁷Co radiation source and a large-angle position-sensitive detector. We tuned the incident -ray beam on and off the Mössbauer effect resonance, and measured diffraction patterns from our textured samples of polycrystalline⁵⁷Fe. Mössbauer effect diffraction dominated over X-ray diffraction for the higher order Bragg peaks.     

关於镧La57的超精细结构

实验上定出的La₅₇的超精细结构常数(a(²D_5/2))/(a(²D_3/2))之比比由单组态的理论计算出的结果约大三倍。要想解释这个差别,一个比较常用的方法就是加入一些组态混合。我们首先考虑到在基态(6s)²(5d)之外再加上一些(6s)(7s)(5d)的混合,并作了详细的计算,得到的结果只能对单组态的理论稍加修正,而距实验值仍相差甚远。其次又考虑到混合一些(5d)²(6s)的态,因为这种组态能量比较低,所以混合的比例可能比较大,於是所产生的修正也比较大。经过一些简单的分析和估计,得出:要能解释实验,则所需混入(5d)²(6s)的比例太大(约为0.36),因此我们认为虽然混入(5d)²(6s)是可能对理论值有较大的修正,但要与实验符合还是相当困难的。     

Fe57 Mössbauer study in cobalt substituted magnetite

The Mössbauer effect has been studied in the mixed ferrites Co _x Fe_3–x O₄ (forx=0.8, 0.9 and 1) with the spinel structure in the temperature range between 78 and 380 K. The composition withx=1, showed an expected Zeeman spectrum with two overlapping magnetic hyperfine patterns related to the Fe³⁺ ions in tetrahedral and octahedral sites. While for samples withx=0.8 and 0.9 the Mössbauer spectrum for each compound was successfully analysed into three different patterns corresponding to the ferric ions placed at the tetrahedral and octahedral sites and ferrous ions at the octahedral sites, indicating no electron transfer between Fe³⁺ and Fe²⁺, where the quantity of cobalt is sufficiently large to be located at the six nearest neighbours to ferrous ions. The Mössbauer effect parameters were calculated for these observed sites and their variation with temperature reported. The reduced hyperfine magnetic fields of the Fe³⁺ (B) ions were found to follow the Brillouin curve forS=5/2 and one third power law. The magnetic ordering temperature was determined to be 815 K and the possible magnetic interactions were discussed.     

Mössbauer spectroscopy on57Fe: NaCl crystals

Mössbauer absorbtion spectra of⁵⁷Fe-doped NaCl crystal were measured and correlated with an adequate electric field gradient computation to describe the dipolar complexes occuring at the decay of Suzuki-phase under thermal treatment and X-ray irradiation. An electrostatic potential of the type was taken into account in the evaluation of EFG tensor.     

Iron-based nanocrystalline alloys investigated by 57Fe Mössbauer spectrometry

Soft magnetic nanocrystalline alloys have attracted great fundamental interest in recent years due to their two-phase structural and magnetic behaviour. We review first the reliability of the fitting procedures of spectra obtained by ⁵⁷Fe Mössbauer spectrometry which is a very efficient tool to investigate such materials. Then, we report the common features which characterise the temperature dependence of Mössbauer spectra; the hyperfine field temperature dependence of both the crystalline grains and the intergranular phase is discussed for different crystalline fractions in order to model the magnetic behaviour of the nanocrystalline alloys.     

邮票上的物理学史(57)--原子核物理学

前面说过的放射性、同位素、中子、裂变、聚变、反应堆都属于原子核物理学.本节讨论原子核物理学更进一步的内容.     

57Fe Mössbauer spectroscopic study of nanostructured zinc ferrite

Nanosize zinc ferrite particles, prepared by nitrate method, were investigated by XRD, TEM, ⁵⁷Fe Mössbauer spectroscopy and VSM. The average particle size in this system varies from 10 to 62 nm as the sintering temperature increases from 300°C to 1,000°C. The lattice parameters in this system are almost constant at a value of ～8.41 Å. The Mössbauer spectra of all the sintered samples show a single doublet. The Mössbauer hyperfine parameters show little change with the change of sintering temperature. The doublets are ascribed to the presence of superparamagnetism in this system, which is also corroborated by the VSM measurements.     

Iron-57 Mössbauer spectroscopic study of fluorinated strontium orthoferrite

A nuclear spin maser of a new type, that employs a feedback scheme based on optical nuclear spin detection, has been fabricated. The spin maser is operated at a low static field of 30 mG by using the optical detection method. The frequency stability and precision of the spin maser have been improved by a highly stabilized current source for the static magnetic field. An experimental setup to search for an electric dipole moment (EDM) in ¹²⁹Xe atom is being developed.     

57Fe Mössbauer study of new multiferroic AgFeO2

The present work reports results of the ⁵⁷Fe Mössbauer measurements on AgFeO₂ powder sample recorded at various temperatures including the points of both magnetic phase transitions. The ⁵⁷Fe Mössbauer spectra of AgFeO₂ measured in the paramagnetic range (T > T _N1) consist of one quadrupole doublet with rather high quadrupole splitting of Δ_300K = 0.66 ± 0.01 mm/s for Fe³⁺ ions. In order to predict the sign of electric field gradient (EFG) at ⁵⁷Fe nuclei, we calculated the lattice contribution to the electric field gradient (EFG) at ⁵⁷Fe nuclei, which emphasized the importance of the dipolar contributions, with resultant oxygen polarizabilities in the range of α _O = 0.83 ų, in agreement with the results obtained previously for other delafossite-like oxides. In the temperature range of T _N2 < T < T _N1, Mössbauer spectra gave clear evidence for the existence of a distribution of the hyperfine magnetic fields H _hf at ⁵⁷Fe nuclei. We present the results of a model fitting of the spectra based on an assumption of the cycloid magnetic structure of AgFeO₂ at T < T _N2. The obtained data were analysed in comparison with published data on Mössbauer studies of oxide multiferroics.     

Nuclear forward scattering of synchrotron radiation from unmagnetized α-57Fe

Nuclear foward scattering of synchrotron radiation from magnetically polycrystalline and partly magnetized -⁵⁷Fe foils has been observed. The forward scattering amplitude in both cases is calculated. The results allow the interpretation of the time spectra from samples which are magnetically polycrystalline or exhibit an unidirectional magnetic texture.     

Time-resolved Mössbauer spectra obtained after 57Mn implantation in Si

A new detector system for the coincidence technique between Mössbauer γ-rays and energetic β-rays originating from ⁵⁷Mn has been developed for in-beam Mössbauer spectroscopy using ⁵⁷Mn implantation. This system enables time-resolved Mössbauer measurements of ⁵⁷Fe at various elapsed times after β ^?-decay of ⁵⁷Mn with sufficient quality. We applied this system to the time-dependent measurement of the site distributions of dilute Fe atoms in n-type Si. It was suggested that Fe atoms were already located at substitutional and interstitial positions in Si within a time of about 100 ns after the β ^?-decay of ⁵⁷Mn, and that the occupancy ratio between these positions was hardly dependent on the elapsed time after the β ^?-decay.     

Untersuchung von Kristalleigenschaften mit Hilfe des Mößbauer-Effekts von Fe57

A further evaluation and discussion of data obtained in a previous investigation on Mößbauer effect in iron compounds has been carried out. In addition to the confirmation of the grouping of line shifts for trivalent and for divalent iron compounds, suggestions for an explanation of the behaviour of complex salts are made. The temperature dependence of the shift, which had been known only for Fe-metal, is shown to be linear in the range of measurement for all substances, which have been investigated, having an astonishing small slope for the complex salts. The quadrupole splitting and its temperature dependence is discussed for the different types of chemical bonds involved. After elimination of the dependences on absorber thickness and temperature from the measured linewidths, it was shown that the source of Co⁵⁷ in Pt has about the natural linewidth and that there is a line broadening in most absorbers increasing with chemical instability. Using the temperature dependence an accurate determination of Debye-Waller factors is possible. These factors show a grouping for salts and for metals respectively.     

高峰值功率1．57μm脉冲激光器的研究

KTP非线性频率转换技术是实现人眼安全激光的有效方法,为了获得高峰值功率人眼安全激光,设计了一种级联式1．06μm泵浦非临界相位匹配环形腔KTP光参量振荡器一光参量放大器,并对其激光输出进行了测试,结果证明该光参量振荡器输出激光波长1．571μm,激光峰值功率42MW,光光转换效率35％,能量稳定度2．5％。该技术已用于计量检测标准光源,并在远程人眼安全激光测距仪、激光雷达等装备中具有应用前景。