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Fibres-based soft magnetic composites (FSMCs) have been prepared by using Fe fibres of different diameters (65, 125, 250 and 500 μm). The Fe fibres were coated with a 3 μm thick layer of Fe3O4 via the blackening process and subsequently compacted at 700 MPa. The X-ray diffraction analysis (XRD) was used to prove the formation of the Fe3O4 coating on the surface of the fibres. The thickness and the uniformity of the coating were analysed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The DC measurements performed on the composite cores revealed that the saturation induction increase from 1.36 to 1.68 T, the maximum relative permeability increase from 550 to 940, and the coercive field decrease from 796 to 454 A/m as the fibre's diameter increase from 65 to 500 μm. By using thinner fibres (65 and 125 μm), composites with low losses and stable initial relative permeability, in the frequency range 50 Hz–10 kHz, can be obtained. To distinguish between different types of losses dissipated by our compacts, and the influence of the fibre's diameter on the different components of the total losses, a numerical model for loss separation is proposed. The comparative evolution of the AC magnetic characteristics of the FSMCs and powder-based SMCs is presented. According to the presented results, this new type of composites can be successfully used to prepare magnetic cores designated to work in the medium to high-frequency range.

Invar 36 (Fe64Ni36) nanocrystalline powders were successfully obtained by the mechanical alloying process. The mechanically alloyed Invar 36 powders were obtained from both, Fe–Ni elemental and Fe–...

A mixture of Ta and 25 mass% Cu elemental powders was subjected to mechanical alloying in a high-energy ball mill up to 60 h. The results are composite particles formed by nanocrystalline Cu and amorphous Ta phases. Thermal stability of amorphous was investigated by DSC. The XRD, FTIR and EDX analyses of Ta–25 mass% Cu powder milled for 60 h performed after DSC at 800 and 900 °C have revealed large amounts of Ta nitride and Ta oxides even though the milling process was done in Ar atmosphere. This is due to high reactivity of Ta fine particles with oxygen and nitrogen from air. During manipulations of the powder (taking samples from vials and its investigation), the adsorption phenomena on its surface occur, and both surface-adsorbed N2 and O2 are processed with powder and embedded in it. While heating of Ta–25% Cu milled powder in DSC, nitrogen and oxygen diffusion into tantalum is activated, and Ta2N and TaO2/Ta2O5 compound forms.

The preparation and characterisation of soft magnetic composite compacts based on hybrid coated nanocrystalline Fe-Si powder are presented. The Fe-Si powder was prepared by mechanical milling of Fe-Si electrical steels sheets up to 20 h. The hybrid coating consists in an electrically insulating phosphate and a polymer layer that covers the Fe-Si particles. The influence of phosphating duration on the particles surface was investigated by SEM, EDX, XRD, and FTIR investigations. The saturation magnetisation of the powders phosphated for 60 s decreases with 17% as compared to the uncoated powder. The influence of the compaction pressure, as well as the phosphating duration, on initial relative permeability and power losses of the compacts was investigated. It was found that increasing the compaction pressure leads to the increase of the compact's permeability and a decrease of the hysteresis losses. A shorter phosphating duration leads to a partial coating with phosphate of the Fe-Si particles and to compacts with higher density characterised by high magnetic permeability.

This work presents a comparative study on the HITPERM type alloy prepared by wet and dry mechanical alloying. The chosen composition for this study was Fe38.5Co38.5Nb7B15Cu1. The powders were obtained via mechanical alloying starting from elemental Fe, Co, Cu powders and the ferroalloys of Nb and B. Mechanical alloying experiments were done using a high energy planetary ball mill Pulverizette 6 under Ar atmosphere. It was observed that for the powder milled in wet milling conditions, using benzene as process control agent, the alloy amorphisation occurs after 40 h of milling. X-ray diffraction patterns highlighted the alloy amorphisation. In the dry milled powder case, the amorphisation did not occur even after 100 h of milling. The thermal stability and the crystallisation kinetics of the amorphous powders were investigated via differential scanning calorimetry and in-situ high-temperature X-ray diffraction. The powders morphology and chemical homogeneity were studied by scanning electron microscopy and X-ray microanalysis. The saturation magnetisation also reveals a difference between wet and dry milled powders versus milling time. The obtained results concerning the alloy amorphisation and its thermal stability are compared with available data of the literature.

Formation of the Ni2MnSn Heusler alloy by solid state reaction from elemental powders was investigated. The solid state reaction was conducted in a planetary ball mill under argon atmosphere up to 28 h of milling. During the milling, after selected intervals samples were collected and studied by X-ray diffraction to record phase changes. After 16 h of milling a two phase mixture (Ni2MnSn with B2 structure and NiMnSn with C1b structure) was found. Further, the thermal stability of the samples was investigated, and phase precipitation was found. The formed phases are ordered Full Heusler (L21) and Ni3Sn2. The formation temperature and their amount evolution versus temperature and milling time is discussed. An inversion of the formation temperature was found for the L21 and Ni3Sn2 phase, during the DSC study, in relation with the milling time. For the B2 compound a stability range on temperature was identified (from 25 to 300 °C), as well as for the L21 and Ni3Sn2 phases (from 400 to 600 °C) in the case of 28 h milled sample. The milled and annealed sample exhibit nanocrystalline state, formation mechanism under temperature was concluded to be by precipitation.

Fe3O4/Ni3Fe composite powder has been synthetized, starting from Fe, NiO and α-Fe2O3 precursors via mechanosynthesis and annealing, varying the alloy/ferrite ratio. The formation of Fe3O4 is noticed for the composite with low alloy content in the case of the samples milled for 10 h. Formation of Ni3Fe and Fe3O4 does not fully occur after milling for 10 h, in either of the cases and as a consequence, the presence of several intermediate phases can be observed. Annealing at 500 °C for 4 h led to an incomplete reaction between the precursors for the un-milled sample. For the milled and subsequently annealed samples, the complete formation of the composite Fe3O4/Ni3Fe occurs at the milling time of 10 h. The DSC measurements reveal a decrease of the temperature required for the Fe3O4 complete formation upon increasing milling time. The first magnetisation curves reveal a decrease of the magnetisation upon increasing milling time. The value of magnetisation after annealing is higher than the magnetisation value of the milled samples as a result of the complete formation of the ferrite phase and Ni3Fe intermetallic compound.

This paper presents a comparative study regarding the preparation of Fe-based amorphous alloys via mechanical alloying (MA) and rapid quenching (RQ). The obtained samples (powders and ribbons) were characterised by X-ray diffraction (XRD), in-situ high-temperature X-ray diffraction (HT-XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) and vibrating sample magnetometry (VSM). By using elemental powders of Fe, Si and B, it was found that amorphisation cannot be achieved by dry MA or RQ. Wet MA using benzene as process control agent (PCA) led to the alloy amorphisation after 20 h of milling. It was proved that the amorphisation via wet MA is possible due to the extra amount of C atoms provided by the PCA decomposition. Using powders obtained by wet MA or a mixture of Fe, Si, B and C elemental powder, amorphous ribbons were obtained by RQ. During the amorphous samples crystallisation, a mixture of α-Fe(Si) and Fe borides is formed. The magnetic measurements showed that the magnetic characteristics of the samples are strongly influenced by the technique used for their preparation.

The paper reports on the preparation and characterisation of a new type of soft magnetic composites in which the ferromagnetic particles are replaced by Fe fibres. The fibres were coated via hydrothermal method with a SiO2 layer having a thickness of 150–200 nm. Also, a hybrid coating was developed by adding a supplementary layer of polymer on top of the SiO2 layer. The coated fibres were compacted via cold pressing at the pressure of 700 MPa. Our results indicate that using only SiO2 as the insulating layer leads to compacts characterised by lower hysteresis losses. However, it seems that during compaction, the SiO2 layer is damaged leading to the development of large eddy currents at high frequencies. Conversely, the additional polymer layer manages to prevent the development of excessive eddy currents in the compact, but with a significant increase of the hysteresis losses of the compacts being observed. A significant improvement of the magnetic characteristics of the fibre-based soft magnetic composites can be achieved by an annealing treatment with the condition of maintaining the integrity of the insulating layer, or minimising the diffusion between the fibres and the SiO2 coating during the annealing.

Result of research concerning the influence of milling conditions on the amorphisation of the Fe75Si20B5 (at.%) alloy is presented. Amorphous powder of Fe75Si20B5 (at.%) was prepared by dry and wet mechanical alloying (MA) route starting from a mixture of Fe, Si and B elemental powders. The mixture was wet/dry milled up to 50 hours. Benzene, oleic acid and ethanol were used as process control agents (PCA) in order to investigate the influence of their chemical composition on the powder amorphisation. The evolution of the powder crystalline structure, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) as well as magnetic measurements versus temperature and field. It is proved that the chemical composition of the PCA (especially the carbon content) plays an important role in the amorphisation process induced by wet MA.

Nanocrystalline Fe-10 wt% Si powders has been obtained by mechanical alloying. The synthesis conditions as well as their influence on the structural and magnetic properties of this soft magnetic alloy have been investigated in the light of several experimental techniques (X-ray diffraction, neutron diffraction, DSC, magnetic measurement, SEM). By X-ray diffraction (XRD) investigations have been highlighted that Fe-Si alloy is formed after 4 h of mechanical milling and the mean crystallite size is down to 14 nm (8 h milled sample). The heat treatment leads to the formation of the Fe 3 Si compound with DO3-type superstructure for low milling times. The saturation magnetisation of the as-milled powders decreases in the first 4 h of milling due to the formation of the Fe-Si alloy. The behaviour of the saturation magnetisation versus milling time and annealing was explained by the different magnetic moment of iron atoms in Fe 3 Si structure. The Curie temperature decreases from 770 °C (the Curie temperature for pure iron) to about 650 °C after 8 h of milling.

The composite/nanocomposite powders of Mn0.5Ni0.5Fe2O4/Fe type were synthesized starting from nanocrystalline Mn0.5Ni0.5Fe2O4 (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn0.5Ni0.5Fe2O4/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn0.5Ni0.5Fe2O4/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe1−xMnxFe2O4/Ni–Fe composite type. The new formed ferrite of Fe1−xMnxFe2O4 type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe1−xMnxFe2O4, Ni structure, FeO, and (NiO)0.25(MnO)0.75 phases.

The nanocrystalline/nanosized mixed manganese–nickel spinel ferrite ${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$ was successfully synthesized by the classical ceramic method followed by mechanical milling. The refinement of the crystallite size is obtained by increasing the milling time up to 120 min. The particles size distribution performed on the milled powder showed a fine ferrite powder. The Neel temperature of ${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$ decreases by increasing the milling time as a result of the structural disorder and it is larger when compared with the manganese ferrite one and lower when compared with the nickel ferrite one. The saturation magnetization of the spinel structure was found to be 2.42 $\mu_{B}$ and it is close to the theoretical one 2.5 $\mu_{B}$ . The saturation magnetization and spontaneous magnetization decrease by increasing milling time. The spontaneous magnetization is reduced more drastically when compared with the saturation magnetization. One of the major causes is assumed to be the spin canted effect induced at the particles surface by milling process.

Nanocomposite powder and compacts of NiFe 2 O 4 /Ni 3 Fe type were synthesized using mechanical milling and spark plasma sintering (SPS) techniques. The samples have been investigated by X-ray diffraction (XRD), laser particles size analysis, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The nanocomposite powder was obtained by mechanical milling in a high planetary ball mill of nanocrystalline NiFe 2 O 4 and nanocrystalline Ni 3 Fe powders. The nanocomposite powder consists from Ni 3 Fe particles covered at the surface with a layer of NiFe 2 O 4 fine particles and NiFe 2 O 4 particles. The nanocomposite particles have the median diameter d 50 of 1.6 μm. The sintering in 400–600 °C temperature range preserve the nanocomposite phases but lead to a high porosity. The nanocomposite compacts consist in Ni 3 Fe clusters surrounded by NiFe 2 O 4 . A sintering temperature of 800 °C leads to a good density for the nanocomposite compacts and to the new phase formation. The new phase is a wustite type (Fe 1− x Ni x O) and is formed at the metal/ceramic interface. A change in the Ni/Fe ratio, in the spinel structure, was evidenced during sintering. Sintering at a temperature of 800 °C, leads to the formation of a mixed iron–nickel ferrite with a very small amount of nickel, Ni 1− x Fe x Fe 2 O 4 .

Amorphisation of Fe75Si20B5 (at.%) alloy has been attempted both by wet and dry mechanical alloying starting from a mixture of elemental powders. Powder amorphisation was not achieved even after 140 hours of dry mechanical alloying. Using the same milling parameters, when wet mechanical alloying was used, the powder amorphisation was achieved after 40 h of milling. Our assumption regarding the powder amorphisation capability enhancement by contamination with carbon was proved by X-ray Photoelectron Spectroscopy (XPS) measurements which revealed the presence of carbon in the chemical composition of the wet mechanically alloyed sample. Using shorter milling times and several process control agents (PCA) (ethanol, oleic acid and benzene) with different carbon content it was proved that the milling duration required for powder amorphisation is linked to the carbon content of the PCA. Differential Scanning Calorimetry (DSC), thermomagnetic (TG) and X-ray Diffraction (XRD) measurements performed to the heated samples revealed the fact that, the crystallisation occurs at 488 °C, thus leading to the formation of Fe3Si and Fe2B. Thermogravimetry measurements performed under H2 atmosphere, showed the same amount of contamination with C, which is about 2.3 wt%, for the amorphous samples regardless of the type of PCA. Saturation magnetisation of the wet milled samples decreases upon increasing milling time. In the case of the amorphous samples wet milled with benzene up to 20 h and with oleic acid up to 30 h, the saturation magnetisation has roughly the same value, indicating the same degree of contamination. The XRD performed on the samples milled using the same parameters, revealed that powder amorphisation can be achieved even via dry milling, just by adding the equivalent amount of elemental C calculated from the TG plots. This proves that in this system by considering the atomic species which can contaminate the powder, they can be used as microalloying elements which could provide the required extra amount of metalloids.

Co-based amorphous alloys were prepared via wet mechanical alloying process starting from elemental powders. The reference alloy Co70Fe4Ni2Si15B9 (at. %) as well as the alloys derived from this composition by the substitution of 5 at.% of Zr or Ti for Si or B (Co70Fe4Ni2Si15B4Zr5, Co70Fe4Ni2Si15B4Ti5, Co70Fe4Ni2Si10B9Zr5 and Co70Fe4Ni2Si10B9Ti5) are obtained in amorphous state, according to X-ray diffraction (XRD) investigation, after 40 h of milling. The calculated amount of amorphous fraction reaches 99% after 40 h of milling. The largest increase of the crystallisation temperature was induced by the substitution of Zr or Ti for Si while, regardless of the type of substitution, an important increase of the Curie temperature of the alloy was obtained. A Co-based solid solution, with Co2Si and Co2B phases, result after crystallisation of the amorphous alloys as proved by XRD investigations. Saturation magnetisation of the alloys decreases upon increasing milling time, however it remains larger than the saturation magnetisation of the reference alloy. This was discussed in correlation with the specificity of the wet mechanical alloying process and the influence of the chemical bonding between Co and metalloids atoms over the magnetic moment of Co.

Manganese substituted nickel ferrites, Ni 1− x Mn x Fe 2 O 4 ( x =0, 0.3, 0.5 and 0.7) have been obtained by a combined method, heat treatment and subsequent mechanical milling. The samples were characterised by X-ray diffraction, differential scanning calorimetry and magnetic measurements. The increase of the Mn 2+ cations amount into the spinel structure leads to a significant expansion of the cubic spinel structure lattice parameter. The crystallite size decreases with increasing milling time up to 120 min, more rapidly for the nickel–manganese ferrites with a large amount of Mn 2+ cations ( x =0.7). After only 15 min of milling the mean crystallites size is less than 25 nm for all synthesised ferrites. The Neel temperature decreases by increasing Mn 2+ cation amount from 585 °C for x =0 up to 380 °C for x =0.7. The magnetisation of the ferrite increases by introducing more manganese cations into the spinel structure. The magnetisation of the milled samples decreases by increasing milling time for each ratio among Ni and Mn cations and tends to be difficult to saturate, a behaviour assigned to the spin canted effect.

Nanocrystalline copper ferrite has been synthesized using a combined method which involves reactive milling, heat treatment and mechanical milling. After 4 h of reactive milling a solid solution between the starting oxides (CuO and α-Fe2O3) and a spinel phase is obtained. Increasing the milling time leads to a decomposition of those phases. After a heat treatment of the 30 h milled sample a single spinel CuFe2O4 phase is obtained. By mechanical milling the crystallite size of the copper ferrite is reduced down to 9 nm after 1 h of milling. For the CuFe2O4 samples milled between 2 and 4 h a decomposition of this phase is remarked and α-Fe2O3 is formed during milling. The spontaneous magnetization of the spinel decreases with increasing the milling time as results of the partial redistribution of the cations in the spinel and of spin canted effect. The magnetization of the milled samples does not saturate due to the presence of very fine ferrite particles which are superparamagnetic.

Soft magnetic Fe 3 O 4 /Ni 3 Fe composite powder has been synthetized, starting from Fe, Ni and Fe 2 O 3 powders via mechanosynthesis and subsequent annealing. The incipient formation of Fe 3 O 4 is noticed for the sample milled for 2 h. Formation of Ni 3 Fe and Fe 3 O 4 does not occur completely after milling for 10 h and as a consequence the presence of a small amount of unreacted Fe 2 O 3 can be found. Subsequent annealing led to the complete reaction between the precursors. Even for the un-milled homogenized mixture of precursors, a partial formation of Ni 3 Fe and Fe 3 O 4 occurs during annealing. For the milled and annealed samples, the complete formation of the composite Fe 3 O 4 /Ni 3 Fe occurs after 6 h of milling. The DSC measurements and the XRD patterns of the samples subjected to DSC analysis revealed the formation of FeO phase for the starting sample and the samples milled short times (up to 1 h). The complete of the Fe 3 O 4 is noticed upon increasing milling time. The first magnetization curves reveal a two-stage evolution for the milled samples. For milling times up to 3 h, when the Fe 2 O 3 phase is still significant, the value of magnetization has tendency to decrease. Due to the progressive Fe 3 O 4 and Ni 3 Fe formation, the value of magnetization increases for the samples milled for longer durations. The value of magnetization after annealing is larger than the magnetization value of the milled samples as a result of complete formation of ferrite phase.

The Hipernik alloy (50Ni50Fe wt. %) was obtained by mechanical alloying. The milling was performed in argon atmosphere, with a ball/powder mass ration of 8:1 for times ranging from 2 up to 20h. The alloy formation was studied by X-ray diffraction. The obtained structure is face cantered cubic, indicating the extension of the γ domain for the Ni-Fe alloys by mechanical alloying. The mean crystallite size was calculated with the Williamson – Hall method. Using scanning electron microscopy (SEM) the morphology and the chemical homogeneity of the powders was analysed. The technological properties of the powders as particle size distribution and flowability are determined as a function of the milling time. The magnetic behaviour of the samples was studied by magnetic measurements under high magnetic fields.

The formation of quaternary 76Ni17Fe5Cu2Cr (wt. %) alloy by mechanical alloying is investigated. The elemental powders of Ni, Fe, Cu and Cr where milled in argon atmosphere in a planetary ball mill for time up to 20 h. Formation of the alloy was checked by X-ray diffraction studies. It is found that the rapid formation of the alloy lead to the rapid establishment of an equilibrium between the welding and fracture process during milling, leading to a constant particle size distribution over a big range of milling time. The morphology of the powders, studied by scanning electron microscopy (SEM) confirms the rapid increase in size. The particle size distribution and the flowability of the powders are also analyzed as a function of milling time. Enhanced magnetization was found for the milled samples, compared to a cast alloy.

Fe73.5Cu1Nb3Si13.5B9 (at.%) amorphous alloy has been prepared from elemental powder mixture by wet mechanical alloying route, using benzene as process control agent (PCA). The powder has been investigated from the structural, thermal and magnetic point of views. After 15 h of wet mechanical milling, the alloy is obtained in nanocrystalline state, further increase of milling time leading to the progressive amorphization of the alloy. Full amorphization of the alloy is reached after 80 h of wet mechanical alloying. A significant decrease of the particle size is observed during alloy formation, the further increase of the milling time leading only to minor changes of the particles size. By DSC investigation, the primary crystallization of amorphous powder was found to take place at around 570 °C leading to the formation of Fe–Si alloy and iron borides. The Curie temperature of the amorphous material is 280 °C. The XRD investigations of the fully crystallized alloy (heated up to 900 °C) reveal the presence of the NbC phase into the alloy microstructure as a result of powder contamination with carbon. The decrease of the saturation magnetization of the powder upon increasing milling time was observed and is discussed in the light of the structural and chemical changes induced by milling process. A post milling annealing at 300 °C leads to the enhancement of the saturation magnetization due to the stress release and the removal of the benzene adsorbed on the powder surface.

Fe-Si alloy with a Si content of 10 wt. % was obtained in nanocrystalline state by mechanical alloying of elemental iron and silicon powders. The mechanical alloying process was carried out in a high energy ball mill (Fritsch, Pulverisette 4) in argon atmosphere. The X-ray diffraction (XRD) studies indicated that after 4 hours of milling the Fe-Si alloy is formed. The mean crystallites size decreases down to 7 nm after 8 hours of milling. The particles morphology investigated by scanning electron microscopy (SEM) showed an evolution during milling process from two different kinds of particles to a one kind of particles with irregular shape. The magnetisation of powders decreases upon increasing the milling time up to 4 hours as a consequence of the Fe-Si alloy formation.

Wet mechanical alloying (MA) were used to prepare amorphous soft magnetic Fe75Si20B5 (at.%) powders starting from elemental powders of Fe, Si and B. The structural, morphological and magnetic properties of the powders were investigated. It was found that wet MA leads to the amorphisation of the alloy after 40 hours of wet milling using benzene (C6H6) as process control agent (PCA). The influence of the wet MA process on the saturation magnetization of the powders was investigated. Amorphous powder of Fe75Si20B5 (at.%) obtained by wet MA route was used to prepare compacts by spark plasma sintering (SPS). The chosen sintering temperature was 800, 850 and 900 oC. Toroidal samples of Fe75Si20B5 (at.%) were investigated in DC and AC magnetization regime and their magnetic properties were correlated with sintering parameters, compacts density and phases evolution during sintering.

The nanocrystalline nickel ferrite (NiFe2O4) was synthesized by reactive milling starting from equimolar mixture of oxides. The iron contamination during milling leads to a solid state reaction between Fe and NiFe2O4 spinel. This reaction starts for a milling time longer than 30 h. A mixed nickel–iron ferrite (Ni1−γFe2+γO4) and elemental Ni are obtained. The evolution of the nickel–iron mixed ferrite during milling and its properties were investigated using X-ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR), Laser Particles Size Analyzer and magnetic measurements. Annealing treatment (350°C/4 h in vacuum) is favorable to the reaction between phases. Replacement of Ni2+ cations by iron cations provided by contamination leads to the increase of lattice parameter value of the spinel structure. The magnetization of the nickel–iron mixed ferrite newly formed is larger than the nickel ferrite magnetization (13.6 μB/f.u. and 6.22 μB/f.u., respectively), due to the magnetic moment of Fe2+ cation which is double as compared to the Ni2+ cation. Magnetization of the milled samples decreases during milling due to the structural changes induced by milling in the nickel–iron mixed ferrite. The annealing induces a reordering of the cations which leads to a larger magnetization.

International audience; Stoichiometric mixture of CuO and alpha-Fe2O3 milled in air up to 30 h was subjected to different heat treatments. The evolution of the heat treated milled powders was investigated by X-ray diffraction (XRD). The CuFe2O4 was partially obtained by milling, the material consisting in a mixture of phases. By applying different heat treatments in air and in vacuum, for 2-6 h, in 500-800 A degrees C temperature range the phases composition of the milled samples is changed. A heat treatment at 500 A degrees C in vacuum favours the formation of delafossite (CuFeO2) and tenorite (CuO) phases. If the same heat treatment is made in air, the CuFe2O4 phase formation with a cubic structure is favoured. Differential scanning calorimetry (DSC) investigation realised in Ar atmosphere revealed two large exothermic peaks. The first one is associated with the formation of the delafossite and tenorite phases and the second one with the formation of CuFe2O4. The XRD patterns of the samples subjected to the DSC measurements present maxima corresponding to the delafossite and cuprospinel (CuFe2O4) phases. For the heat treatment at 600 A degrees C in air the phases present in the sample are the same as for the annealing performed at 500 A degrees C: CuFe2O4, alpha-Fe2O3 and CuO. The heat treatment in air at 800 A degrees C leads to the complete reaction between the different phases and the formation of CuFe2O4 phase in whole the sample volume. The CuFe2O4 ferrite crystallises after this heat treatment in two crystal systems: cubic and tetragonal.

International audience; Nanocrystalline nickel ferrite (NiFe2O4) has been synthesized from a stoichiometric mixture of oxides NiO and alpha-Fe2O3 in a high energy planetary mill. An annealing at 350 degrees C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 +/- 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure.

International audience; Nanocrystalline Rhometal (36Ni64Fe, wt. %) powders have been obtained by mechanical alloying under argon atmosphere. The initial mixture was milled up to 20 h. In order to eliminate internal stresses and to improve the solid state reaction annealing at 350 °C was performed for 4h. The alloy formation is obtained after 8 h of milling. A mean crystallite size of 10 ± 4 nm is obtained after 20 hours of milling. The magnetization values for the as-milled samples are between that of the starting sample and that of the as cast one. The evolution of the magnetization versus the milling time is discussed. The thermomagnetic analysis shows the Curie temperatures confirming the alloy formation by milling. As a result of the solid state reaction by milling means, a continuous decrease of the magnetization with increasing the temperature is recorded, similarly to the behaviour of the classical cast alloy.