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The binary oxide AlVO4 is being proposed as a new gas sensor material. An X-ray investigation, IR spectrum analysis, resistivity and a calculation of the electronic structure of this compound have been carried out in order to determine its structural, absorptive and sensor properties. The fragment [Al3V3O23]18− is the chain chosen to study the electronic properties of AlVO4 in the framework of the frontier orbital theory and the interaction between molecules has been described by the Molecular Electrostatic Potential (MEP). The vibration analysis and the simulated infrared spectrum (IR) were calculated for the unit [Al3V3O23]18− and a comparative analysis with the experimental spectrum of AlVO4 is also presented.

In recent years several ferroelectric thin films have been studied at microwave frequencies; lead zirconate titanate (PZT) and barium-strontium titanate (BST) has been widely investigated. However, the microwave dielectric properties of strontium-bismuth tantalate (SBT) have not yet been investigated so widely [1]. The purpose of this work is the microwave characterization of the dielectric properties of an SBT thin film biased at different DC voltages. The dielectric properties of SBT make it a good material for the production of FERAM memories. Microwave characterizations may show other properties that could promote the SBT as good candidate for capacitors to be employed also in microwave circuits (e.g. resonators and filters). In this work a study of high frequency dielectric properties has been performed and equivalent circuit model has been used to correct the measurements.

AlVO4 thin films were prepared by infrared Nd:YAG pulsed laser deposition on two different substrates (polycrystalline Al2O3 and monocrystalline MgO). The distance between the target-substrate (30 mm) and the partial oxygen pressure (0.14 mbar) during the deposition process were chosen taking into account the previous experiences with other oxides. The substrate temperature was varied between 300 and 600 °C finding an optimum at about 400 °C. At higher temperatures, the vanadium seems to evaporate from substrate surface with a strong change of stoichiometry. Preferential growth of AlVO4 films in the direction (022), were grown on MgO substrates. A very high sensitivity of these films to a flux of NO2 gas is also shown.

PhFe 11 CrO 19 polycrystalline samples were prepared by the chemical coprecipitation method. X-ray diffraction and Mossbauer spectroscopy confirm the formation of the M-type hexagonal structure. Time dependence of the magnetization was recorded on the demagnetization curve of the hysteresis loop. It is well described by a simple logarithmic law but also non-logarithmic behavior was detected. A two-peak dependence of the viscosity coefficient S with the applied field was encountered. Considering reversible susceptibility measurements and a M(H) curve at constant dM/dt in the irreversible susceptibility determination, the calculated activation volume as a function of the applied field shows two well defined zones. The zones observed in the activation volumes are related to the two local maxima that the total susceptibility exhibits. It points to the fact that the viscosity study is sensible enough to characterize this system, encountering two apparent activation volumes.

A simple method for preparing polycrystalline bulk PbFe12O19 hexaferrite has been developed. Ceramic samples were prepared using the ceramic method, and any lead deficiency can be compensated by a correct X-ray diffraction analysis by the Rietveld refinement method and a further addition of PbO. Adequate sintering conditions are necessary to obtain the single-phase compound.

Ferroelectric thin films have been investigated intensely by many researchers over the past decade, but some important phenomena that influence the electrical properties have been overlooked. This work addresses the lead enrichment, which is observed on the surface of lead zirconate titanate films. The XPS compositional profiles of PZT films prepared using different thermal treatments are presented and correlated with the preparation conditions. The segregation profiles are explained in terms of a simple oxidation model that induces the diffusion of lead to the surface. The ionic diffusion also induces self-polarisation, commonly seen in ferroelectric films. The implications on the electrical properties of ferroelectric films, particularly, imprint of the polarisation state, are also discussed.

The structure, microstructure and magnetic transitions of Er 3 Fe 29− x V x ( x =0.5 and 1) based ternary alloys have been investigated. The compounds annealed at the interval temperature 1073–1223 crystallize in a disordered Th 2 Ni 17 structure type with T c =385 ( x =0.5) and 408 K ( x =1). Chemical analysis of sample Er 3 Fe 28 V 1 annealed at T equal to 1203 K ( x =1) showed the presence of three phases, with compositions Er 2 (Fe, V) 16,77 (2:17), Er 1 (Fe, V) 6,24 (1:7) and Er 3 (Fe, V) 29,9 .

AlVO4 is a relatively new sensor material derived from V2O5/Al2O3 mixtures to selectively detect NO and NO2 gases. Previous studies carried out in order to determine its structural, absorptive and sensory properties indicate that the AlVO4 is not the only single phase. This work deals with the synthesis of the compound by the ceramic and the nitrate decomposition methods, and by the sol gel route. The Rietveld refinement of the compound was carried out in order to determine its crystal structure. Single phase of AlVO4 was successfully obtained via the nitrate decomposition and the sol gel methods. Thereafter, films prepared by the sol gel route were deposited on alumina and Si/SiO2/Pt substrates and characterized by SEM and X-ray diffraction. The electric characterization of the AlVO4 on alumina substrate film is also presented.

Reliability issues have hampered the adoption of ferroelectric thin films by the microelectronics industry. One of these is imprint, an important problem affecting the performance of ferroelectric non-volatile memories. This paper presents the effects of the low temperature pyrolysis step on the chemical and physical properties of SrBi 2 Ta 2 O 9 films. A comparison of the hysteretic properties and composition profiles shows that control of the oxidising conditions during pyrolysis is critical to the dielectric properties. Data from this work and from the literature have been used to construct a model that explains the origin of surface depletion and segregation, self poling and as-grown imprint in ferroelectric films.

Ferroelectric thin films based on PZT (65/35) and PZTN (65/35/4) were prepared by the chemical solution deposition using alkoxide precursors. The existence of the perovskite phase was confirmed in each film, with a strong degree of [111] orientation. After deposition of a top electrode, a sandwich structure Au/Ferroelectric/Pt has then been created in order to study the electrical properties. Ferroelectric as well as fatigue behavior has been characterized. Also, the photocurrent generated by an unpoled sample has been measured to correlate the photoresponse with previous optical results.

The effects of Ti and TiN adhesion layers, used below the Pt bottom electrode, on the purity, phase distribution and electrical properties of ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films have been examined and compared. Changes in electrode morphology were observed as a function of temperature, using atomic force microscopy (AFM) and scanning electron microscopy (SEM). A distinct improvement was seen when TiN is used; there are fewer shorting capacitors and the remnant polarisation of the ferroelectric increases markedly. However, the adhesion is not as good. Secondary ion mass spectrometry (SIMS) shows that when Ti/Pt bottom electrodes are used, Ti diffuses through the Pt film causing spurious phases to crystallise in the SBT film. These depth profiles also show evidence of Bi diffusion to the surface of the oxide film and through the Pt towards Ti rich regions.

Magnetic and Mo ssbauer measurements have been performed on polycrystalline samples of Ga substituted M-type hexagonal ferrites having compositions PbFe12−xGa x O19 (0 9 are paramagnetic at all temperatures. The magnetic moments of the non substituted Fe3+ ions in the spin-up predominant sublattice do not have the same temperature dependence, because of the presence of non magnetic Ga3+ ions in the neighbouring lattice sites. For x 3, the faster decline of the saturation magnetisation can be attributed to the onset of non collinear magnetic order.

PbFe12O19 hexaferrite thin films with a high degree of orientation in the perpendicular direction have been deposited by pulsed laser ablation on 1×1-cm2 (0001) sapphire substrate at 700°C under 3.0 mbar partial pressure of high purity oxygen. The anisotropic character of the films was demonstrated by a remanence ratio of 86% in the perpendicular direction in contrast with to 20% in the parallel direction to the film plane. The X-ray diffraction analysis confirmed this orientation, showing only the (0001) lines of PbFe12O19 compound. The hexagonal lattice parameters determined were a=5.885 A and c=23.066 A. Moderate values of coercive field (2.5 kOe) and saturation magnetisation (165 emu/cm3) were obtained.

The effects of low temperature baking on properties of SrBi2Ta2O9 films have been examined. The morpholgy is strongly influenced by the heat treatment chosen. A slow heating rate and an oxidising atmosphere give films on which larger and inhomogeneous grains were seen by AFM. Additionally, ToF-SIMS shows that this heat treatment increases the chemical homogeneity of the ferroelectric film. Contrasting effects are seen; the furnace treatment increases the remnant polarisation but rapid thermal treatments reduce the leakage currents. Keywords strontium bismuth tantalate, SBT, heat treament, SIMS, metallorganic decomposition (MOD), memories.

Pulsed laser ablation deposition has been used to grow polycrystalline PbFe 12 O 19 thin films with high coercivity on Si/SiO 2 substrates. The influence of the substrate temperature (550–775°C) and the oxygen pressure (1.0–3.0 mbar) on the magnetic properties during the deposition is reported. The crystallisation of PbFe 12 O 19 thin films occurs in the temperature range of 600–750°C, which is somewhat lower than that for the Sr and Ba hexaferrites, which crystallise in the range of 750–850°C. M-type lead hexaferrite films with high saturation magnetisation (280 emu/cm 3 ) and high coercive field (3.8 kOe) were grown using a substrate temperature of 700°C and a pressure of 3.0 mbar of oxygen. These films were observed to be isotropic, with an M r / M s ratio of ∼0.5.

In this work an example of the application of glancing angle X-ray diffraction (GAD), scanning (SEM) and transmission (TEM) electron microscopy techniques, on the study of the phase distribution and microstructure of PbZr0.52Ti0.48O3 films deposited by two different methods, sol–gel and laser ablation, on different substrates, is reported. The investigations performed on the samples allowed us to obtain information on the phase distribution inside the films, on the diffusion processes occurred during the crystallisation treatments, on the presence of ferroelectric domains and on the structure of the columnar grains. The results showed that the electrical behaviour could be correlated to the microstructure of the films suggesting the best deposition conditions.

Magnetic and Mossbauer measurements have been performed on polycrystalline substituted M-type hexagonal ferrites of compositions PbFe12−xScxO19 (x = 0, 0.5, 1, 1.5) and PbFe12−xInxO19 (x = 0, 1, 2). The substitution of the Fe3+ by Sc3+ and In3+ ions perturbs the axial magnetic order giving rise to angled magnetic structures. From the values of the quadrupole splitting of the Fe57 14.4 keV level, measured above and below the Curie temperatures, the angle between the magnetic moment of the Fe3+ ions in various sublattices and the hexagonal c-axis have been deduced. At 77 K the measured angles do not exceed 20° and depending on x are different for different sublattices. The dependence of x on the saturation magnetisation at 0 K, expressed in Bohr magnetons, differs markedly in Sc and In containing compounds, partly due to the different substitution probability of iron in the spin up and spin down sublattices, and also due to the different spin canting angles.

Rare-earth transition-metal intermetallics with the Nd3(Fe,Ti)29-type structure with R=Nd, Pr have been synthesized. The as-spun ribbons show a broad magnetic transition between 400 and 500 K. After annealing over a range of temperatures, 723–1373 K, and for times in the range 15–50 min, multiphase samples with the R3(Fe,Ti)29, R(Fe,Ti)12, R2(Fe,Ti)17 and α-Fe phases are obtained. The optimum conditions are: for R=Nd the samples spun with a velocity of 30 m s−1 and annealed at 1373 K for 25 min contain Nd3(Fe,Ti)29 as a main phase, 67 wt.%, with some Nd(Fe,Ti)12 and α-Fe; for R=Pr the samples spun with a velocity of 20 m s−1 and annealed at 1323 K for 25 min contain 88 wt.% Pr3(Fe,Ti)29 with some Pr2(Fe,Ti)17 and α-Fe. These samples present Curie temperatures typical for the Nd3(Fe,Ti)29 and Pr3(Fe,Ti)29 compounds. The room-temperature saturation magnetization is 124.2 and 138.7 A m2 kg−1 for R=Nd and 135.0 and 118.9 A m2 kg−1 for R=Pr, before and after annealing, respectively. The annealed ribbons show grain sizes of

The melt spinning of a NdFeB alloy of stoichiometric composition was investigated under various ambient gas pressures, from atmospheric pressure, 100 kPa (760 Torr) to vacuum, 0.13 Pa (10 −3 Torr). Gas pockets were observed on the roll contact surface of ribbons produced at pressures close to atmospheric, whilst a reduction in pressure, to 50 kPa (380 Torr) caused the disappearance of the gas pockets. The absence of the gas pockets led to more consistent magnetic properties for the nanocrystalline ribbon.

PbFe 12 O 19 powders were obtained by thermal decomposition of hydroxide–carbonate coprecipitated salts and metal–organic precursors at 920°C. Significant microstructural differences have been found between both specimens. The MOD powder comprised submicronic particles of remarkably high coercivity (5 kOe), and the magnetization mechanism was dominated by coherent rotation. In contrast, the coercivity for chemically coprecipitated powders was very poor (1.6 kOe), when compared with Ba- and Sr-compounds prepared following the same method, a behavior associated with excessive grain growth. Cell parameters, microstructure, Curie temperature, hysteretic properties, anisotropy field and the saturation magnetization as a function of the temperature in the interval 77–300 K are reported.

The variation of the tetragonal distortion (c/a) with particle size of Pb(Zr, Ti)O3 nanoparticle thin films prepared by the sol–gel technique is reported. The tetragonal distortion of the unit cell, which is related to the spontaneous polarization, decreases exponentially with size and vanishes at 16 nm. This distortion was correlated with the used additive in the preparation processing and crystallization temperature of the films, and the existence of a critical grain size for the ferroelectric phase transition was observed. The phase transition was monitored by X-ray diffraction, scanning electron microscopy, and electrical measurements.

Strontium titanate thin films were studied with X-ray diffraction and atomic force microscopy during growth at different pressures and temperatures. The nucleation process on top of the islands grown was directly observed with high-resolution. The surface morphology of the films was found to depend on the ambient oxygen pressure and substrate temperature during growth. The films were grown by pulsed laser deposition at different ambient oxygen pressure. The surface roughness of the films decreased with decreasing ambient oxygen growth pressure and with increasing substrate temperatures. The high nucleation probability on top of the films results in an effective mass transport on top of the first-layer islands.

Nucleation and growth of strontium titanate (SrTiO 3 ) films, prepared by pulsed laser ablation deposition, has been investigated during on a (100) silicon substrate surface, using atomic force microscopy. A nucleation kinetic model has been derived from an analysis of the particle size distribution. The reconstructed nucleation trend was characterised by a systematic behaviour: the nucleation rate, negligible at the beginning, reaching a maximum after a certain time and tending to zero for longer deposition time. This behaviour prompted the design of a simple model which correlates these phenomena to two specific aspects: i) the nucleation occurs at certain limited number of sites on the substrate surface; ii) the nucleation process shows a temperature-dependent incubation time. In this model, the incubation time is related to the formation time of a ‘critical SrTiO 3 cluster’. The size of the critical cluster is determined both by thermodynamic quantities and by the amount of interface misfit strain energy of SrTiO 3 lattice with respect to substrate.

An understanding of the growth mechanisms of ferroelectric lead zirconate titanate films is fundamental to the preparation of optimal devices. This work presents the results of X ray diffraction analysis and cross-section transmission electron microscopy obtained on Pb(Zr 0.52 Ti 0.48 )O 3 , and correlates them with electrical properties and preparation conditions. The particular preparation method chosen has demonstrated that the phase which tends to form below 550°C has the pyrochlore structure. Intermediate crystallisation of the film can result in discontinuities if the correct temperatures are not used and spurious phases form at the free surface.

The present work describes the preparation of chromium substituted magnetoplumbite ferrites from nitrate salts, and the effect of Cr on its structural and magnetic properties. Powders with nominal composition PbFe 12-x Cr x O 19 (1.0 ≤ x ≤ 6.0) were obtained by thermal decomposition at 920 °C of coprecipitated hydroxide-carbonate mixed salts. A complete substitution of Fe 3+ by Cr 3+ was found and the influence of Cr on cell parameters, ordering temperatures and hysteretic properties are reported. The results are discussed and compared in connection with behaviour observed in isostructural Ba- and Sr-compounds.

PbFe 12 O 19 hexaferrite powders with high coercivities were obtained using modifications to the traditional ceramic route. Mossbauer and X-ray diffraction measurements indicates that the M-type hexagonal phase coexist with the α-Fe 2 O 3 phase at the temperature range of 800 T T >900°C, the magnetic properties are drastically affected as a consequence of the volatility of PbO.

Pulsed laser ablation deposition has been used to grow polycrystalline Pb–M and Sr–M thin films with high coercivity on Si/SiO 2 substrates. The influence of the substrate temperature (550–800 ◦ C) and the oxygen pressure (1.0–3.0 mbar) on the magnetic properties during the deposition is discussed. The Pb–M hexaferrite thin films crystallise at the same temperature range as Sr–M thin films, but with inferior coercivities. In both cases, the best values of iHc (3.8 kOe, Pb–M films and 5.0 kOe for Sr–M thin film) are very close to the best value of sintered ceramic hexaferrite (5.0 kOe Pb–M and 6.0 kOe Sr–M). The isotropic character of the films was confirmed by a Mr/Ms behaviour near to 0.5. © 2003 Elsevier B.V. All rights reserved.

The transport of material from target to substrate has been monitored in the pulsed laser deposition of Pb(Ti0.48Zr0.52)O3 films on p‐doped Si(100) using two in situ diagnostics, namely plume fluorescence spectroscopy and plume ion mass spectrometry. The as‐grown PZT films are specular, with thicknesses which decrease from 350 to 250 nm on a radius 5 mm from the center and show a dielectric hysteresis with typical remanent polarizations and coercive fields of 0.2 μC/cm2 and 124 kV/cm, respectively. The analysis of the plume fluorescence emission and ionic yield indicates that oxidation of the ablated material occurs during transport from target to substrate and that, in order to grow ferroelectric thin films, the substrate should be located in the region of the plume where the relative concentrations of metal oxides and clusters increase.

In the present work the metallorganic decomposition technique has been applied to grow high-coercivity isotropic polycrystalline BaFe 12 O 19 thin films on ZrO 2 /Si substrates. The influence of several growth parameters on the magnetic properties, such as the film thickness, the annealing temperature (500–850°C) and the atmosphere during thermal treatments (oxygen and air), is reported. Barium hexaferrite formation starts at 600°C, the reaction being completed within relatively short times; above 700°C, a beneficial effect of an O 2 atmosphere on i H c was found. In these films particles tend to behave as single domain in the thermically demagnetized state.

The effects of mechanical grinding on the magnetic and structural properties and on the phase formation of Dy-Fe-(B, C) alloys have been studied. X-ray diffraction, Mossbauer spectroscopy and thermomagnetic analysis show that there is a decomposition of the Dy 2 Fe 14 (B, C) phase accompanied by the formation of α-Fe. In addition, for boron rich alloys magnetic phases which are revealed in the TMA curves disappear during the measurement. The magnetic measurements showed a gradual fall in coercivity at longer grinding times. The magnetisation falls initially and then rises, due to the amorphisation and decomposition of the original phases and the formation of the α-Fe.

The effect of temperature and atmosphere during the crystallization process on electrical and reliability characteristics of ferroelectric capacitors, obtained by sol-gel deposition of lead zirconate titanate films, have been examined for non-volatile memory applications. Films with good ferroelectric properties were achieved after 600 and 650 °C, 1 hour crystallization in a O2 atmosphere: a remanent polarization of about 20 μC/cm2 and a coercive field of 125 kV/cm was obtained with a durability factor better than 108 cycles. The results point out that in 5/48 lead zirconate/titanate films, where a morphotropic phase boundary exists, fatigue more likely results from a stress relief process than from charge migration.

A scanning friction force microscope has been used to study the surfaces of lead zirconate titanate thin films prepared by sol-gel and pulsed laser ablation. As well as mapping the topography of the films the friction force has proven to be a sensitive tool which can be used to detect compositional changes. Although the laser deposited films had some larger defects up to 500 nm, the grains had a smooth texture (roughness = 2–5 nm). Sol-gel films had grain sizes of the order of 150 nm and roughness of 20–50 nm. Zirconium rich films also had “rosettes” approximately 1 μm in diameter and raised 200 nm above the surrounding matrix. The technique was sensitive enough to discern chemical differences at the grain boundaries and between the “rosettes” and the matrix.

The structural and magnetic properties of deformed powders of M-type Baferrite, obtained by mechanical grinding, have been investigated using X-ray diffraction, Mossbauer spectroscopy, thermomagnetic analysis, and magnetic measurements. The rapid decrease in the magnetization after short grinding times in air is attributed to the formation of a phase which is paramagnetic at room temperature but at 150 K the phase behaves like a spin-glass, with antiferromagnetic short-range order. From Mossbauer spectra this phase has at least five non-equivalent sites of iron with hyperfine interaction field values Hrf(77 K): H1=38.69; H2=37.01; H3=36.14; H4= 34.31 and H5=30.96 MA/m, and a magnetic moment μFe = 2.1μB. At longer grinding times the deformed BaFe12O19 samples were found to be thermodynamically unstable and decomposed partially into α-Fe2O3 and Fe3O4.

A W-type hexagonal ferrite of composition Sr(ZnLi 0.5 Fe 0.5 )Fe 16 O 27 has been prepared by ceramic technique using ball milling followed by heat treatment at 1100, 1200 and 1320°C for different times. The samples were examined by thermomagnetic analysis, X-ray diffraction, magnetic and Mossbauer measurements. W-type single-phase compounds were obtained by heating the samples at 1320°C but only polyphase material was obtained after heating to 1100 and 1200°C. The samples treated at 1320°C for 5 h had the best intrinsic magnetic properties: σ s = 89 ± 1 emu⧸g, H A = 13.8 kOe and T C = 432°C. The Mossbauer spectra give evidence of a magnetic order, in agreement with a hypothesis of selective occupation by Zn 2+ and Li + cations of the tetrahedral and octahedral spin-down sublattices, respectively.

Scanning force and friction microscopy (SFFM) has, for the first time, been applied to investigate the morphology and phase structure of Pb(Zr, Ti)O3 ferroelectric thin films, deposited by sol-gel. The topographic characterization (roughness 20–50 nm, grain size 150–500 nm) reveals the presence of clusters of grains (rosettes) in zirconium rich films. The friction measurements show that the rosettes and the surrounding material are composed of different phases. Quantitative comparisons of the friction forces are performed.

The manufacture of multilayer capacitors based on barium titanate requires improved precursor powders. In this paper the dielectric properties of barium titanate ceramics made from hydrothermally precipitated material are compared with those powders obtained commercially and prepared by calcination. The greater porosity of hydrothermal powders tends to reduce their effective dielectric constant but preheating them to 950 ‡C before sintering produced high density ceramic with higher values of ɛr. The dielectric losses of these materials are higher than those produced by traditional methods. Their low Curie temperatures (106–8 ‡C) are related to the high strontium concentration (4.7 mol%) present in the starting materials. The grain sizes of these ceramics are less sensitive to sintering temperature than those made using calcined powders, with no anomalous grain growth.

The kinetics of the growth mechanism of Hg1−xCdxTe films made using open tube isothermal vapour phase epitaxy (ISOVPE) is discussed, and two new parameters in the process are included with respect to the previous models: surface reaction and the use of Hg1−xCdxTe sources with low values of x. A comparison between experimental data and the theoretical predictions of Cd composition profile and film thickness suggest that the surface reaction can be considered to be a limiting factor in the growth process.

Single crystals of Zn l-x Mn x Cr 2 0 4 have been grown by the chemical vapour transport (CVT) technique using chlorine as the transport agent. The zinc chromite grew with little difficulty. The presence of manganese chromite liquid caused the ampoules to crack when the crystals rich in manganese were grown. In addition, when the spinels were grown with nominal starting compositions x > 0.5, the condensation of MnCI 2 caused the crystals grown to be depleted in manganese. A thermodynamic study of the closed tube system has been done in order to determine the most favourable conditions for growth and calculate the ranges of temperature and chlorine pressure most suitable to avoid the segregation of manganese. Single crystals of different compositions were analyzed by X-ray diffractometric methods. Magnetic susceptibility measurements suggest a spin-glass-like behaviour which is explained by the existence of a cluster-glass state.

Single crystals of Zn1−xMnxCr2O4, where x=0–1, were grown by the chemical vapour transport (CVT) technique using chlorine as the transport agent. A thermodynamic study of both systems, (ZnCr2O4 + MnCr2O4-Cl2 and Zn1−xMnxCr2O4-Cl2, was done in order to investigate the effect of spurious species, i.e. MnCl2(liq), on the transport of the mixed spinel, and structural investigations using X-ray diffraction were carried out. Susceptibility measurements as a function of temperature from 2–300 K for the different compositions are reported, and the magnetic phase diagram was determined as a function of composition and temperature.

Alloys in the series Fe 80− x Cr x Si 10 B 10 (0≤ x ≤14) were prepared by rapid quenching from the melt, using the technique of melt spinning in a controlled argon atmosphere in order to produce amorphous ribbons. Mossbauer spectra, magnetic measurements and Curie temperature ( T C ) measurements were performed. The effect of the substitution of Cr for Fe on T C , and magnetic properties was studied and, as expected, a significant decrease in T C was observed with increasing Cr content. Since, for these alloys, the crystallisation temperature, T x is well above T C , they have potential uses in switching devices and temperature sensors.

The experimental dependence of the initial thermomagnetic curves upon the demagnetization field acting on M-type barium ferrite fine particle samples is examined in the present study. The experimentally measured thermomagnetic curves have been compared with a recently developed theoretical model. It is found that there is a very good agreement between the calculated curves and the experimental ones in a weak external field.

The Dy 2 Fe 14 B 1- x C x (0 ⩽ x ⩽ 1) alloys have been studied in order to understand the main differences in the phase formation between the carbides and borides. The amorphous alloys were prepared by melt spinning and the recrystallisation was studied by differential thermal analysis, X-ray diffraction and Mossbauer spectroscopy. The results reveal some interesting features about the crystallisation mechanism of these amorphous alloys.