Thermomagnetic Annealing Research Articles

Influence of size effects and granule distribution by size on optical and magneto-optical properties of nanocomposites

In this paper, the spectral dependences of the transverse Kerr effect (ТКЕ) are studied experimentally and theoretically. The results are obtained for deposited and annealed samples with a corresponding variation in the size of the granules. It was found that thermomagnetic annealing leads to an increase in the ТКЕ value in magnetic nanostructures, while the most noticeable changes in the effect value were observed in the range of medium and high concentrations of the magnetic component in the visible region of the spectrum. The expediency of using the effective medium approach for calculating magneto-optical effects in granular systems, taking into account the size distribution of granules within the lognormal distribution of granules, is shown. Based on this approach, the main features of the optical and magneto-optical properties of nanocomposites are explained by the example of (Co45Fe45Zr10)X(Al2O3)1–X. All calculations are performed in the Bruggemann approximation, which effectively describes the properties of nanostructures in the region of average concentrations. Size effects are clearly manifested in nanocomposites and have a significant impact on the optical and magneto-optical properties of nanocomposites, especially in the IR region of the spectrum, which is associated with intraband transitions. Taking into account the particle size distribution makes it possible to significantly improve the description of such promising inhomogeneous nanostructures. The solved problem is very important and relevant both from the fundamental point of view – the study of magneto-optical, optical and transport phenomena in nanocomposites – and from the point of view of the great possibilities of their application in modern electronics and nanoelectronics. Taking into account the size effects and the particle size dispersion makes it possible to find new promising functional materials and control their properties in a wide spectral range.

Enhancement of magnetic and microstructural properties in Fe-Cr-Co-Mo-V-Zr-Y permanent magnetic alloy

Abstract The 43-xFe-28Cr-23Co-3Mo-2V-1Zr-xY; x = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 wt% permanent magnets were produced through casting, thermomagnetic annealing and aging treatments. Magnetic and microstructural properties were improved by Y addition and process optimization. The Y element modifies the morphology of ferromagnetic F-Co rich phase, introduces filed anisotropy and contributes in coercivity enhancement. XRD and EDS results showed that Y free 43Fe-28Cr-23Co-3Mo-2V-1Zr alloy is composed of Fe-Co-V (54.4%) and Cr-Mo-Zr (45.6%) phases while Y doped 41Fe-28Cr-23Co-3Mo-2V-1Zr-2Y alloy is consists of Fe-Co-V-Y (55.7%), Cr-Mo-Zr (29.3%) and Y1Co5 (15%) magnetic phases. Micrographs obtained by scanning transmission electron microscope elucidate nanostructural exchange coupled Fe-Co-V-Y (15–20 nm), Cr-Mo-Zr and Y1Co5 (10 nm) phases for 41Fe-28Cr-23Co-3Mo-2V-1Zr-2Y alloy. Pole figures and ODFs deduced sharp magnetic {1 1 0}〈0 0 1〉 textures or preferential orientation of Fe-Co rich rod like particles. Henkel plots deduced strong ferromagnetic exchange interactions between the magnetic phases. The 43Fe-28Cr-23Co-3Mo-2V-1Zr alloy yields Br of 0.71 T, Hc of 97 kA/m and (BH)max of 51.3 kJ/m3 which were remarkably improved to Br of 1.05 T, Hc of 130 kA/m and (BH)max of 61.6 kJ/m3 with 41Fe-28Cr-23Co-3Mo-2V-1Zr-2Y alloy.

Structure and Magnetic Properties of Fe-Cu-Nb-Si-B with Various Niobium Concentration

The microrelief of the contact, free sides and cuts of three metal alloys with various niobium contents were studied. It is shown that samples with high niobium content are X-ray amorphous, the alloys FeCu1Si16B6, FeCu1Nb3Si16B6are characterized by an amorphous-crystalline structure. The change in the magnetic characteristics and electrical resistance of alloys in the course of thermomagnetic annealing is studied. It is shown that an increase in the Nb content in an alloy increases its temperature stability and the temperature of the onset of crystallization processes.

Phase, microstructure and magnetic properties of 45.5Fe-28Cr-20Co-3Mo-1.5Ti-2Nb permanent magnet

The 47.5-xFe-28Cr-20Co-3Mo-1.5Ti-xM; M = Nb; x = 0.5, 1, 1.5, 2.0, 2.5, 3.0 (wt%) permanent magnets have been investigated after solution annealing, thermomagnetic annealing and step-aging process. Alloys were prepared by vacuum melting and casting technique. Magnets with improved properties were developed through a modified thermal treatment cycle. Solution annealed specimens depict equiaxed α phase grain size of 250 µm while optimally thermomagnetic treated and step aged magnets yield ultra-fine Fe-Co nanorods (10 nm) precipitates in Cr-Ti-Nb matrix. The Nb addition to 47.5Fe-28Cr-20Co-3Mo-1.5Ti alloy expands the α phase structure by suppressing the nonmagnetic phases at annealed state and promotes shape anisotropy for spinodal phases in final treated samples leading to the improvements of magnetic properties. Spinodal phases preferentially aligned and elongated close to applied field direction and retained strong Goss {1 1 0}〈0 0 1〉 orientations. The 45.5Fe-28Cr-20Co-3Mo-1.5Ti-2Nb magnet reveals Hc of 86.9 kA/m, Br of 1.24 T and (BH)max of 57 kJ/m3. High coercivity and remanence in the magnets are attributed to the ideal shape anisotropy of Fe-Co rich nanorods or nanowires.

Structural, magnetic and mechanical properties of Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 nanocrystalline hard magnet

Microstructural, magnetic and mechanical properties of Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 nanocrystalline hard magnets produced by rapid solidification technique and subsequent thermo-magnetic annealing have been investigated in this study. X-ray diffraction analysis revealed that the as-cast Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet has 60% Nd2Fe14B, 16% α-Fe, 9% Fe3B and 15% amorphous phases, whereby, Nd2Fe14B being the majority phase. Thermomagnetic annealing induces a complete crystallization of Nd2Fe14B, α-Fe, Fe3B and amorphous phases and establishes ideal volume fractions between phases leading to improvement in magnetic properties. Scanning and transmission electron microscopy show nano-scaled hard Nd2Fe14B grains surrounded with soft α-Fe and Fe3B grains. The Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet annealed at 993 K for 15 min shows values of coercivity iHc, remanence Br and maximum energy product (BH)max up to 861 kA/m, 0.68 T and 81.9 kJ/m3, respectively. Compressional stress strain measurements elucidated that mechanical properties of alloys are affected by the morphology of phases as well as crystal structure. As-cast Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet demonstrates the hardness (Hv) of 960 ± 20 and compressive stress (σf) of 1270 ± 10 MPa, which tend to decrease by thermo-magnetic annealing process.

Effects of Zr alloying on the microstructure and magnetic properties of Alnico permanent magnets

Alnico-8 permanent magnets were produced through casting and subsequent thermal treatment process. Magnetic alloy of nominal composition 32.5 Fe-7.5 Al-1.0 Nb-35.0 Co-4.0 Cu-14.0 Ni-6.0 Ti were prepared by arc melting and casting technique. The Zr was added to 32.5 Fe-7.5 Al-1.0 Nb-35.0 Co-4.0 Cu-14.0 Ni-6.0 Ti alloy ranging from 0.3 to 0.9wt%. The magnets were developed by employing two different heat treatment cycles known as conventional treatment and thermo-magnetic annealing treatment. The samples were characterized by X-ray diffraction method, Scanning electron microscope and magnetometer by plotting magnetic hysteresis demagnetization curves. The results indicate that magnetic properties are strongly depended upon alloy chemistry and process. The 0.6wt% Zr added alloys yielded the best magnetic properties among the studied alloys. The magnetic properties obtained through conventional heat treatment are Hc=1.35kOe, Br=5.2kG and (BH)max=2MGOe. These magnetic properties were enhanced to Hc=1.64kOe, Br=6.3kG and (BH)max=3.7MGOe by thermo-magnetic annealing treatment.

Optimization of parameters of the thermomagnetic annealing of amorphous ferromagnetic cores for flux-gate transducers on the criterion of minimum noise

The results of the experimental researches for minimizing the own noise level of the flux-gate sensors with the cores based on the amorphous magnetic material Co 68 Fe 3 Cr 3 Si 15 B 12 are presented. The measurements of the sensor noise level with the cores, which were subjected to the thermo-magnetic treatments with different parameters, are carried out. It is shown, that the annealing at the temperatures 430-445 °C followed by the unregulated cooling with the time constant 400 s provides the minimal noise level of the fluxgate sensors.

The influence of the magnetic history on the loop shift behavior of Fe-based amorphous ribbons

The asymmetrical hysteresis loops were observed for the annealed Fe65Co15Si5B15 amorphous ribbons. The curves, which shift from the zero point of H axis with a unilateral step magnetization, exhibit the special magnetic features of the ribbons. A few magnetic crystalline phases were identified in the amorphous matrix of annealed ribbons by microstructure measurement. It was also found that the Z-oriented local magnetic domains emerge in the surface of ribbons with the loops shift behavior. Subsequent magnetic torque measurement indicated that the unidirectional magnetic anisotropy was induced in the amorphous ribbons with proper thermomagnetic annealing. These obtained evidences support our understanding that the magnetic history caused by thermomagnetic treatment plays a main role in promoting the formation of the asymmetrical loops.

Exchange bias behaviour of amorphous CoFeNiSiB ribbons

A dramatic exchange bias behaviour was found in superior soft Co58Fe5Ni10Si11B16 amorphous ribbons with proper thermomagnetic annealing conditions. This characteristic, which was directly obtained at room temperature, is quite different from that of the traditional ferromagnetic–antiferromagnetic system. The observation of microstructure indicated that the matrix of the annealed ribbons with the exchange bias behaviour includes a few crystalline phases. The magnetic domains of the ribbon surface were scanned to clarify the configuration of local magnetic moments. A subsequent magnetic torque measurement revealed that unidirectional magnetic anisotropy was induced in the amorphous ribbons with a longitudinal field. The obtained evidence supports our point of view that the local crystalline phases in the ribbons along with the longitudinal thermomagnetic treatment are the key factors in promoting the formation of an exchange bias. A simple phenomenological discussion was developed to expound this interesting behaviour in ribbons.

In situ monitoring of the magnetization rotation of a soft layer using microwave permeability measurements

This paper demonstrates that the monitoring of the microwave permeability of thin films is an efficient way to obtain a real-time information on the in-plane uniaxial anisotropy, both in magnitude and in direction. Theoretical guidelines required to extract relevant information on the in-plane uniaxial anisotropy are presented. This technique has evidenced a fast decrease in the anisotropy followed by a slower rotation process of the uniaxial anisotropy in a Co 91Nb 6Zr 3 film during thermo-magnetic annealing.

Variations of the induced anisotropy in a-CoZr(M) (M=Mo,Ta) films as a function of thickness and deposition parameters

In amorphous CoZrM films the field induced uniaxial anisotropy Ku exhibit singular properties if the effective deposition temperature is 300 K: Hk increases strongly with decreasing film thickness d for 25 nm<d<50 nm. Ku is reduced by a thermomagnetic annealing, but reconstructed spontaneously at 300 K. Ku is a growth induced structural anisotropy, its comportment is strongly affected by the intrinsic free volume that is larger, thinner is the layer.

Variations of the induced anisotropy in a-CoZr(M) (M=Mo,Ta) films as a function of thickness and deposition parameters

In amorphous CoZrM films the field induced uniaxial anisotropy K u exhibit singular properties if the effective deposition temperature is 300K: H k increases strongly with decreasing film thickness d for 25 nm<d<50 nit. K u is reduced by a thermomagnetic annealing, hut reconstructed spontaneously at 300 K. K u is a growth induced structural anisotropy, its comportment is strongly affected by the intrinsic free volume that is larger, thinner is the layer.

Giant magnetoimpedance and induced anisotropy in joule-heated and conventionally annealed Co-based amorphous materials

The effect of induced magnetic anisotropy on GMI has been studied in Co 71Fe 4B 15Si 10 melt spun amorphous ribbons, using two different techniques of thermomagnetic annealing. Quasi-static hysteresis loops were measured at controlled induction. From the quasi-static hysteresis loop evolution, the value of the macroscopic anisotropy K u induced by the field annealing treatment was determined. The evolution of the domain structure was observed using a Kerr-effect apparatus.

Magneto-optical investigation of micromagnetic structure of Fe-rich amorphous ribbons and wires

The results on the magneto-optical investigation of the magnetization processes and near-surface micromagnetic structure (MMS) of Fe-rich soft magnetic amorphous ribbons and wires are presented. The strong dispersion (in macro- and microscale) of magnetic anisotropy in the studied samples was discovered. In consequence of it, their local magnetic properties were very inhomogeneous. It was proved that magnetization processes of the samples realize by means of incoherent rotation of local magnetization vectors. The buckling and curling modes of the magnetization reversal were observed in ribbons and wires correspondingly. It was established that at a some value of magnetic field the blocking of magnetization processes exists. It was discovered that thermomagnetic annealing of the studied ribbons strongly influence on their local magnetic properties and MMS.

Thermomagnetic annealing of amorphous CoZrM (M=Zr, Nb, Ti) and CoZrPt thin films Relationship between the relaxation process of the induced anisotropy K u and the local atomic order

The uniaxial magnetic anisotropy of amorphous Co 95- x Zr 5M x (M=Zr, Nb, Ti) and Co 91- x Zr 9Pt x thin films present large variations as a function of the pressure of the sputter gas. An adequate thermomagnetic annealing permitted to show that K u is the sum of two contributions K a u+ K s u, where K a u and K s u are the i nduced anisotropies related to the local anisotropy of the octahedral-icosahedral and trigonal-type clusters, respectively. Co 91- x Zr 9Pt x films exhibit a peculiar thermomagnetic relaxation that is explained by the reversibility of the pseudodipolar anisotropy and the thermal instability of trigonal-type clusters resulting from the substitution of Pt.

Thermomagnetic annealing of soft amorphous metallic alloys monitored by in situ resistance and magnetoresistance measurements

This study concerns structural relaxation in sputtered Co-metal amorphous films (here, Co8.15Zr8.5Pt10) taking place during isochronal and isothermal thermomagnetic treatment. The aim is to improve the stability of the films and to reduce their induced magnetic anisotropy. In these materials, the topological short-range ordering (TSRO) directly connected to the amorphous film stability is irreversible, whereas the chemical short-range ordering (CSRO), which has to do with magnetic anisotropy, is reversible. With a view to maintaining strict control over both TSRO and CSRO and to treat them separately, equipment was constructed to perform thermomagnetic anneals up to 900 K combined with quenches with initial rates of 500 K s−1. In the course of these treatments, resistance and magnetoresistance measurements were used to follow accurately, with a sensitivity better than 10−5, the evolution of TSRO and of induced anisotropic field HK without resorting to any other characterization than those made with this apparatus. Under these conditions several isochronal and isothermal anneals were carried out which show that: (1) TSRO and CSRO can easily be differentiated, and (2) HK can be reversibly changed or controlled at will.

Induced anisotropy of a-Co-Metal thin films. Relationship between the magnitude and kinetics of Ku and the local atomic order

In amorphous CoZrM (M = Zr, Nb, Ti) films the field induced uniaxial anisotropy K u varies largely as a function of the pressure of the sputter gas. An adequate thermomagnetic annealing allows to determine the respective contributions to K u of the pseudodipolar and structural anisotropy. A correlation is observed between the annealing kinetics and the local structure.

Magnetic and structural properties of amorphous CoTi soft ferromagnetic thin films. I. Magnetic properties.

The magnetic and related structural properties of amorphous ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ti}}_{\mathrm{x}}$ ferromagnetic thin films are reported. The concentration range investigated is 0.14\ensuremath{\le}x\ensuremath{\le}0.22. In this first part of the paper the as-obtained magnetic properties are presented. The films were prepared by rf sputtering, and the deposition process was performed in a magnetic field applied parallel to the film surface. The magnetic properties were studied systematically as a function of the pressure of sputtering gas ${P}_{\mathrm{Ar}}$ and rf input power ${W}_{\mathrm{rf}}$. For the whole concentration range and the overall deposition parameters the ferromagnetic resonance revealed standing spin-wave spectra corresponding to magnetically highly uniform samples. The deposition parameters affect essentially the in-plane uniaxial anisotropy energy ${K}_{u}$ and the coercive field ${H}_{c}$ along the easy axis. ${K}_{u}$ shows a bell-shaped variation as a function of ${P}_{\mathrm{Ar}}$. The maximum value of ${K}_{u}$ (${K}_{u}$${)}_{\mathrm{max}}$ is obtained for the same ${P}_{\mathrm{Ar}}$ in the whole concentration range studied. The physical origin of ${K}_{u}$ was determined by performing thermomagnetic annealing, which revealed that depending on the value of ${P}_{\mathrm{Ar}}$ used, ${K}_{u}$ is related to a pseudodipolar or structural mechanism or a combination of both. The small variations of ${H}_{c}$ with deposition parameters are also shown and discussed in terms of the change in the local structure.

Magnetic and structural properties of amorphous CoTi soft ferromagnetic thin films. II. Structural properties.

The magnetic and related structural properties of amorphous ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ti}}_{\mathrm{x}}$ ferromagnetic thin films are reported. The concentration range investigated is 0.14\ensuremath{\le}x\ensuremath{\le}0.22. In this first part of the paper the as-obtained magnetic properties are presented. The films were prepared by rf sputtering, and the deposition process was performed in a magnetic field applied parallel to the film surface. The magnetic properties were studied systematically as a function of the pressure of sputtering gas ${P}_{\mathrm{Ar}}$ and rf input power ${W}_{\mathrm{rf}}$. For the whole concentration range and the overall deposition parameters the ferromagnetic resonance revealed standing spin-wave spectra corresponding to magnetically highly uniform samples. The deposition parameters affect essentially the in-plane uniaxial anisotropy energy ${K}_{u}$ and the coercive field ${H}_{c}$ along the easy axis. ${K}_{u}$ shows a bell-shaped variation as a function of ${P}_{\mathrm{Ar}}$. The maximum value of ${K}_{u}$ (${K}_{u}$${)}_{\mathrm{max}}$ is obtained for the same ${P}_{\mathrm{Ar}}$ in the whole concentration range studied. The physical origin of ${K}_{u}$ was determined by performing thermomagnetic annealing, which revealed that depending on the value of ${P}_{\mathrm{Ar}}$ used, ${K}_{u}$ is related to a pseudodipolar or structural mechanism or a combination of both. The small variations of ${H}_{c}$ with deposition parameters are also shown and discussed in terms of the change in the local structure.

Experimental study of regions of reversed magnetization in an amorphous layer of Co70Fe5Si10B15

The characteristics of the distribution of magnetization and remagnetization of microsections of the surface in the amorphous alloy Co70Fe5Si10B15, prepared in the form of thin ribbons, were studied by the magnetooptical method. It was found that the magnetization I on the surface of the amorphous ribbon studied was strongly nonuniform. It was established that heat treatment (HT) of the sample leads to the appearance of regions of reversed magnetization in the surface layer of the ribbon, while thermomagnetic annealing reduces the nonuniformity of I. The conservation of the transverse component in the HT sample in fields where the magnitude of the component of magnetization parallel to the length of the ribbon remains virtually unchanged suggested that a domain structure of the magnetization “ripple” type, owing to the strong microdispersion of the magnetic anisotropy, is realized in this sample.