Effect of structural relaxation on Curie temperature and magnetostriction investigated by magnetoelastic waves in metglas

Summary Magnetoelastic wave amplitude, a, was measuredvs. the temperature during thermal cycles in Metglas 2826. When the Curie temperature,T _C, has been reached, theA value vanishes due to the fall of the magnetoelastic coupling in the paramagnetic state. This allows evaluation of theT _c temperature. The latter increases after the iterated thermal treatments while the magnetic anisotropyK _u decreases. Also theA amplitude, measured at room temperature after the subsequent thermal treatments, shows an increasing behaviour. The values ofK _u ,T _c andA approach saturation after the same number of thermal cycles; this suggests that the structural relaxation produced by annealing is the microscopic mechanism governing all the three physical quantities. In particular we explain the connection betweenK _u andA by means of the longitudinal magnetostriction.

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Riassunto L'ampiezza delle onde magnetoelastiche,A, è stata misurata in funzione della temperatura eseguendo cicli termici nel Metglas 2826. Raggiunta la temperatura di Curie,T _C l'ampiezzaA si annulla a causa della transizione dell'accoppiamento magnetoelastico nello stato paramagnetico. Ciò ci mette in grado di misurare la temperaturaT _C; quest'ultima aumenta in seguito ai ripetuti trattamenti termici mentre l'anisotropia magneticaK _u diminuisce. Anche l'ampiezzaA, misurata a temperatura ambiente dopo i trattamenti termici, mostra un andamento crescente. I valori diK _u,T _c eA tendono alla saturazione dopo lo stesso numero di cicli termici; ciò suggerisce che il rilassamento strutturale prodotto dalla ricottura è il meccanismo microscopico che regola le tre grandezze fisiche menzionate. In particolare noi mostriamo cheK _u eA sono legati dalla magnetostrizione longitudinale.

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Резюме Измеряется зависимость амплитуды магнитноупругой волны,A, от температуры в течение температурных циклов в металлическом стекле 2826. При достижении температуры Кюри,T _c, величинаA обращается в нуль из-за уменьшения магнитноупругой связи в парамагнитном состоянии. Это позволяет оценить темпаратуру Кюри,T _c. Температура Кюри увеличивается после повторных температурных обработок, тогда как магнитная анизотропияK _u уменьшается. Также отмечается увеличение амплитудыA, измеренной при комнатной температуре после последовательных температурных обработок. ВеличиныK _u,T _c иA приближаются к насьщению после одинакового числа температурных циклов. Это результат предполагает, что структурная релаксация, обусловленная отжигом, представляет микроскопический механизм, определяющий все три физические величины. В частности, мы объсняем связь междуK _u иA с помощью продольной магнитострикции.

     

Diffusion and solubility of some interstitial impurities in deformed metals

Summary The problem of impurity diffusion accompanying segregation phase nucleation on dislocations has been studied using the approximation of the local equilibrium with respect to the impurity distribution between the volume solution and dislocation regions. It has been shown that the known experimental data on diffusion and solubility of some interstitial impurities in cold-worked b.c.c. and f.c.c. metals and alloys can be described in the framework of the dislocation trap model. The characteristics of the impurity segregation regions near dislocations have been obtained from the treatment of the diffusion and solubility data for the systems. On the basis of the crystallographic and thermodynamic considerations the possibility of the existence of such segregation phase regions along dislocations in the systems in question has been shown.     

Residual thermal strain of metals in heating-cooling cycles

Summary Metallic samples subjected to heating-cooling cycles undergo a permanent change in their length. The difference between the initial length and the length at the end of the cycle (residual strain) depends on the maximum temperature attained during the cycle. This dependence of residual strain on the maximum temperature of the cycle is similar for all of the examined metals (polycrystalline copper, aluminium, iron, gold, lead and single-crystal copper). Upon further increasing this temperature, the metal residual strain changes from positive to negative values. The temperature at which the maximum positive residual strain occurs is characteristic for each metal. The value of the residual strain and the temperature at which it changes its sign depend on the previous thermal history of the metal.     

Partial anisotropy induced by low-field thermomagnetic treatment of noncrystalline ribbons

Summary The initial development of the transverse anisotropy induced by magnetic annealing is investigated for magnetizing field values which are much smaller than the ones generally employed. Measurements of Young modulus and longitudinal magnetostriction not only show their relation with induced anistotropy, as predicted in a previous paper, but also enable us to calculate the easy magnetization direction. The results are in agreement with the distributed relaxation time theory.

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Riassunto La cinetica dell’anisotropia trasversale, indotta da trattamenti termomagnetici, è stata studiata per valori del campo magnetico notevolmente piú piccoli di quelli generalmente impiegati. Si dimostra la relazione del modulo di elasticità lineare e la magnetostrizione longitudinale con l’energia di anisotropia indotta, come già predetto in un precedente lavoro. In base alla coerenza dei risultati abbiamo potuto stimare la direzione di facile magnetizzazione indotta da trattamenti termomagnetici parziali. I risultati sono in accordo con l’ipotesi teorica di tempi di rilassamento distribuiti.

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Резюме Исследуется начальное развитие поперечной анизотропии, индуцированной магнитным отжигом, в магнитных полях, напряженности которых очень малые по сравнению с обычно используемыми. Измерения модуля Юнга и продольной магнитострикции не только показывают связь с индуцированной анизотропией, но также позволяют вычислить направление легкого намагничивания. Полученные результаты согласуются с теорией.

     

Magnetic, magnetoelastic and structural properties of Co82 P18, Fe80B13 Si4C3 and Fe73.5 Cu1Nb3 Si15.5B7 amorphous ribbons after consecutive heat cycles in vacuum

Summary  Amorphous ferromagnetic ribbons, with basic differences in production technique, in thermal stability and devetrification modality, were investigated to compare some of their magnetic, magnetoelastic and structural properties after repeated annealing cycles in vacuum. In particular, differences in structural relaxation, measured by Differential Scanning Calorimetry, were related to effects on magnetic permeability, magnetoelastic wave amplitude and crystallization occurrence.     

Phosphoric acid activation—Functionalization and porosity modification

4,4′-Bis(maleimidodiphenyl) methane (BM) and divinylbenzene (DVB) copolymers with different compositions were used for production of carbons by carbonization and phosphoric acid activation. It has been shown that both BM and DVB polymers are good carbon precursors which show the same potential to produce carbonaceous material. However, despite cross-linked nature of all polymers, BM softens before formation of coke giving non-porous material. Phosphoric acid activation of polymer precursor increased the yield, surface area and pore volume as compared to acid-free heat treatment. Phosphoric acid activation of polymer precursor resulted in carbon material containing 6-8% of phosphorus and considerable amount of surface acidic groups of four types (total 2.6-3.2 mmol/g) which are responsible for metal ion adsorption from aqueous solutions.     

Effects of annealing temperature on structure and magnetic properties of amorphous Fe61Co27P12 nanowire arrays

Arrays of Fe₆₁Co₂₇P₁₂ nanowire with an aspect ratio about 70 were prepared in anodic aluminum oxide templates by electrodeposition. The influences of annealing temperature on structure and magnetic properties of Fe₆₁Co₂₇P₁₂ nanowires were studied. When the specimens were annealed below 400 °C, there are no obvious changes in structure except relaxation. With the annealing temperature increasing from 400 to 600 °C, the Fe-Co phase is detected by X-ray diffraction and Mössbauer spectra. The crystalline fraction and hyperfine field can be derived from Mössbauer spectra. The room temperature magnetic hysteresis loops show that the coercivity and squareness of the nanowire arrays in parallel to the wire axis increase with the increasing of annealing temperature, which mainly attributes to the strengthening of anisotropy.     

Excitonic photoluminescence characteristics of amorphous silicon nanoparticles embedded in silicon nitride film

We have investigated the photoluminescence (PL) properties of amorphous silicon nanoparticles (a-Si NPs) embedded in silicon nitride film (Si-in-SiN_x) grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. The PL spectrum of the film exhibits a broad band constituted of two Gaussian components. From photoluminescence excitation (PLE) measurements, it is elucidated that the two PL bands are associated with the a-Si NPs and the silicon nitride matrix surrounding a-Si NPs, respectively. The existence of Stokes shift between PL and absorption edge indicates that radiative recombination of carriers occurs in the states at the surface of the Si NPs, whereas their generation takes place in the a-Si NPs cores and the silicon nitride matrix, respectively. The visible PL of the film originates from the radiative recombination of excitons trapped in the surface states. At decreasing excitation energy (E_ex), the PL peak energy was found to be redshifted, accompanied by a narrowing of the bandwidth. These results are explained by surface exciton recombination model taking into account there existing a size distribution of a-Si NPs in the silicon nitride matrix.     

Micromagnetic study of magnetic domain structure and magnetization reversal in amorphous wires with circular anisotropy

In this work we present a detailed numerical investigation on the magnetic domain formation and magnetization reversal mechanism in sub-millimeter amorphous wires with negative magnetostriction by means of micromagnetic calculations. The formation of circular magnetic domains surrounding a multidomain axially oriented central nucleus was observed for the micromagnetic model representing the amorphous wire. The magnetization reversal explained by micromagnetic computations for the M-H curve is described in terms of a combined nucleation-propagation−rotational mechanism after the saturated state. Results are interpreted in terms of the effective magnetic anisotropy.     

Normal- and oblique-incidence reflection of semi-infinite crystals: Adiabatic approach with excitonic effects

Summary Excitonic reflection spectra of semi-infinite crystals are calculated within Stahl's coherent wave approach to band gap dynamics. Stahl's constitutive equations are solved by an adiabatic approximation in a surface region of the thickness z₀ and exactly in the bulk. The depth z₀ determines a region where the repulsive surface potential plays a decisive part for the motion of electrons and holes. The method yields simple analytical expressions for the reflectivity and for the bulk polariton amplitudes both for the normal and for the oblique incidence. Calculated reflectivity curves are compared with experimental data for various semiconductors and various angles of incidence showing a fairly good agreement.

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Riassunto Si calcolano gli spettri di riflessione eccitonica di cristalli semi infiniti entro l'approccio d'onda coerente di Stahl alla dinamica dell'intervallo di banda. Le equazioni costitutive di Stahl si risolvono con un'approssimazione adiabatica in una regione di superficie di spessore z₀ ed esattamente nel volume. La profondità z₀ determina una regione in cui il potenziale di superficie repulsivo ha un ruolo decisivo per il moto degli electtroni e delle lacune. Il metodo rende semplici espressioni analitiche per la riflettività e per le ampiezze del polaritone di volume sia per l'incidenza normale che per quella obliqua. Si confrontano le curve di riflettività calcolate con i dati sperimentali per vari semiconduttori e vari angoli d'incidenza mostrando un accordo abbastanza buono.

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Резюме Вычисляются экситонные спектры отражения для полубесконечных кристаллов в рамках подхода когерентных волн Сталя к динамике ширины запрещенной зоны. Решаются конститутивные уравнения Сталя с помощью адиаватического приближения в поверхностной области для толщины z₀ и точно в объеме. Глубина z₀ определяет область, где поверхностный потенциал отталкивания играет суцественную роль для движения злектронов и дырок. Предложенный метод дает простые аналитические выражения для овоих случаев нормального и наклонного падения. Вычисленные кривые отражательной срособности сравниваются с экспериментальми данными для раэличных полупроводников и различнях углов падения. Обнаружено довольно хорошее соответствие.

     

Electronic structure and magnetism in 4d-transition metal clusters

We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (O_h) and icosahedral (I_h) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of O_h and I_h clusters as a function of the atomic number along the 4 d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations. Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998     

Shape and thickness effects on the magnetization reversal of Py/Cu/Co nanostructures

We present an experimental investigation of the magnetization reversal process in NiFe/Cu(10 nm)/Co circular and elliptical nano-elements with different thickness of the magnetic layers. The results obtained using element sensitive X-ray resonant magnetic scattering (XRMS) were compared with the previous measurements showing that the dipolar interlayer coupling favours the antiparallel alignment of the two magnetization layers at remanance. In the case of circular shape, the increased thickness of the ferromagnetic layers stabilizes the antiparallel alignment of the layers over a wider field range. A similar effect, accompanied by a delay in the onset of the antiparallel alignment, is observed in the case of elliptical nano-elements and applying the external field along the longer axis of the elements, due to the additional shape anisotropy.     

The effects of annealing on Au/pyronine-B/MD n-InP Schottky structure

Thin film of non-polymeric organic compound pyronine-B has been fabricated on moderately doped (MD) n-InP substrate as an interfacial layer using spin coating technique for the electronic modification of Au/MD n-InP Schottky contact. The electrical characteristics have been determined at room temperature. The barrier height and the ideality factor values for Au/pyronine-B/MD n-InP Schottky diode have been obtained from the forward bias I-V characteristics at room temperature as 0.60 eV and 1.041; 0.571 and 1.253 eV after annealing at 100 and 250 °C, respectively. An increase in annealing temperature at the Au/n-InP Schottky junction is shown to increase the reverse bias leakage current by about one order of magnitude and decrease the Schottky barrier height by 0.027 eV. Furthermore, the barrier height values for the Au/pyronine-B/MD n-InP Schottky diode have also been obtained from the C-V characteristics at room temperature as 1.001 and 0.709 eV after annealing at 100 and 250 °C, respectively. Finally, it was seen that the diode parameters changed with increase in the annealing temperature.     

Influence of annealing temperature on the formation, microstructure and magnetic properties of spinel nanocrystalline cobalt ferrites

Nanocrystalline cobalt ferrites were synthesized by a simple, general, one-step sol–gel auto-combustion method. An interpretation based on the measurement of the adiabatic flame temperature and the amounts of gas evolved during reaction had been proposed for the nature of combustion. The influence of annealing temperatures on the magnetic properties was investigated. The microstructure was characterized by means of X-ray diffractometer (XRD) and transmission electron microscopy (TEM). It was found that the particle size and magnetic properties of the as-prepared ferrite samples showed strong dependence on the annealing temperature. The coercivity initially increased and then decreased with increasing annealing temperature whereas the particle size and saturation magnetization continuously increased.     

退火对B掺杂纳米金刚石薄膜微结构和电化学性能的影响

采用热丝化学气相沉积法制备B掺杂纳米金刚石薄膜,并对薄膜进行真空退火处理,系统研究了不同退火温度对B掺杂纳米金刚石薄膜的微结构和电化学性能的影响.结果表明,当退火温度升高到800 ℃后,薄膜的Raman谱图中由未退火时在1157,1346,1470,1555 cm^-1处的4个峰转变为只有D峰和G峰,说明晶界上的氢大量解吸附量减少,并且D峰和G峰的积分强度比I_D/I_G值变为最小,即sp²相团簇     

Metal-induced solid-phase crystallization of hydrogenated amorphous silicon: dependence on metal type and annealing temperature

We report on metal (Cr, Ni, or Pd)-induced solid-phase crystallization (MISPC) of plasma-enhanced chemical-vapor-deposited hydrogenated amorphous silicon at annealing temperatures ≤600 °C. MISPC is found to significantly reduce the thermal budget of crystallization at annealing temperatures as low as ∼400 °C. The lowest achievable annealing temperature is found to depend on the metal type. The metal type is also found to influence grain size and the conductivity of the polycrystalline silicon. Received: 21 June 1999 / Accepted: 20 October 1999 / Published online: 23 February 2000     

H-mode inductive coupling plasma for PVC surface treatment

An inductively coupled plasma machine has been modified to be able to apply working powers in the order of 1 kW, thus switching to the real inductive H-mode. The plasma is generated by applying a 13.56 MHz radio-frequency to a λ/4 antenna outside the plasma chamber in low pressure conditions. The working gas is argon at pressure in the range from 10 to 100 Pa. With this high power source we have been able to perform plasma etching on a poly(vinyl-chloride) (PVC) film. In particular the effect of the plasma is the selective removal of hydrogen and chlorine from the sample surface. The action of the high power plasma on the sample has been proved to be much more effective than that of the low power one. Results similar to those obtained with the low power machine at about 300 W for 120 min, have been obtained with the high power source at about 600 W for 30 min. The superficial generation of a conductive layer of double C=C bonds was obtained. The samples have been investigated by means of ATR spectroscopy, FIB/SEM microscopy and micro-electrical measurements, which revealed the change in charge conductivity.     

Mo掺杂4H-SiC的磁性和光学性能的第一性原理研究

基于第一性原理密度泛函理论（DFT）的广义梯度近似（GGA）的平面波赝势法（PBE）,计算了4H-SiC的本征体系、过渡金属元素Mo单掺杂4H-SiC体系的电子结构、磁性和光学特性。结果表明：Mo掺杂将导致4H-SiC由本征非磁性变为p型磁性半导体材料,其带隙值由2.88 eV 变为0.55 eV。当Mo掺杂浓度为1.359×1021 cm-3时,磁矩为0.98 ,这表明掺Mo后的4H-SiC材料可以作为自旋电子元器件的备选材料。此外,Mo掺杂4H-SiC体系在（100）和（001）方向的静态介电常数分别为3.780和3.969。介质函数虚部不为0的起始点发生红移,表明掺杂使电子更容易跃迁。     

Quark distributions in nuclei and nuclear effects on nucleon structure functions

Extended quark distribution functions are presented obtained by fitting a large amount of experi-mental data of the ι-A DIS process on the basis of an improved nuclear density model. The experimental data of ι-A DIS processes with A≥ 3 in the region 0.0010 ≤ x ≤ 0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened.     

Quark distributions in nuclei and nuclear effects on nucleon structure functions

Extended quark distribution functions are presented obtained by fitting a large amount of experimental data of the l-A DIS process on the basis of an improved nuclear density model. The experimental data of l-A DIS processes with A≥3 in the region 0.0010≤x≤0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened.