Amorphous and nanocrystalline Fe–Ni–Zr–B ribbons as sensing elements in magnetic field sensors

Fe_81−xNi_xZr₇B₁₂ (x=20$x=20$, 30, 40) melt-spun alloys were investigated as potential new material applied as a sensing element of a fluxgate-type high-sensitivity magnetic field sensor. The sensitivity of the magnetometer was increased by about 60% by using the amorphous or nanocrystalline Fe₄₁Ni₄₀Zr₇B₁₂ alloy, compared with a standard reference sensing material. Application of this material can also extend the temperature range of the operation of the device.     

Laser patterning of Fe–Si–B amorphous ribbons in magnetic field

Site-specific nano-crystallization in an amorphous soft magnetic Fe–Si–B alloy was induced via laser processing on a magnetic substrate. The microstructure evolution was characterized using site-specific transmission electron microscopy, and the results are rationalized by diffusion-based calculations. A clear variation in grain-size and spatial distribution is observed at the center region compared with edge regions of the laser track. Additionally, the nano-crystalline phase exhibits a crystallographic texture at the edge region, whereas a random texture is obtained at the center of the laser track. The evolution of structure, size, and morphology of grains are explained by the influence of magnetic field-enhanced thermal effect on nucleation rate during crystallization.     

Zr and Hf microalloying in an Al–Y–Fe amorphous alloy. Relation between local structure and glass-forming ability

The effects of the addition of small amounts of Zr and Hf (0.5–3%) on the atomic structure of Al₈₈Y₇Fe₅ metallic glass were examined from extended X-ray absorption fine structure (EXAFS) experiments to better understand the influence of these microadditions on the glass-forming ability of this alloy. Measurements at the Zr K and Hf LIII absorption edges allowed the local structures around Zr and Hf atoms to be determined. The same Al environment was found for the different concentrations, consisting of a small cluster extending up to 4.5 Å around the Zr atoms and up to 6 Å around the Hf ones. Although the clustering effect is smaller in the Zr neighbourhood, a drastic shortening of the nearest Zr–Al distance is shown, providing evidence for some covalent character to the bonding, in line with the increased glass-forming ability found in the alloys made with the Zr microaddition.     

Phase composition and magnetic structure in nanocrystalline ferromagnetic Fe–N–O films

The chemical and phase compositions and structure of the Fe–N–O films produced by reactive dc magnetron sputtering (in Ar or Ar + N₂ gas mixture atmospheres) under different conditions (energy parameters of magnetron, residual pressure in the magnetron chamber after preliminary pumping, operating pressure in gas mixture) have been investigated by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and vibrating sample magnetometry. Impurity of nitrogen and oxygen, which are present in the sputtered films, participate in the formation of their phase composition and determine its features. Some phenomena inherent in the nanocrystalline films in the metastable state were found. These are the formation of supersaturated bcc interstitial αFe-based solid solution and precipitation of α’ nitrous martensite with bct crystal lattice. The magnetic structure of the Fe–N–O films, which is characterized by the existence of stochastic domains discovered by correlation magnetometry method, is discussed in terms of the random anisotropy model. It was found that two modes of the magnetic anisotropy field of stochastic domains are formed, which determine the existence of two modes of the coercive field found in the magnetic hysteresis loops.     

Optimisation of soft magnetic properties in Fe–Cu–X–Si13B9 (X=Cr,Mo, Zr) amorphous alloys

In the present paper a group of Fe–Cu–X–Si₁₃B₉ (X=Cr, Mo, Zr) amorphous alloys has been examined by applying different experimental techniques—magnetic permeability, magnetic after-effect, coercive force and electrical resistivity measurements. It has been shown that their soft magnetic properties can be optimised by 1-h thermal annealing at the temperature close to the crystallisation temperature. This leads to an increase of permeability and a decrease of coercive force, thermal instability (magnetic after-effect intensity) and electrical resistivity of the material. The optimisation effect is discussed in terms of different processes—(i) a formation of a nanocrystalline phase with the grain size much smaller than the ferromagnetic exchange length, (ii) an annealing out of microvoids formed during the fabrication process and also (iii) a decrease of the effective magnetostriction constant. The temperature of optimisation annealing treatment is always higher than the Curie temperatures of the materials and varies approximately linearly with the atomic radius of the alloying additions.     

Magnetic properties of high-Bs Fe–Cu–Si–B nanocrystalline soft magnetic alloys

In the present study, the magnetic properties and microstructures of newly developed Fe–Cu–Si–B alloys prepared by annealing the melt-spun ribbon have been studied. The average size and number density of nanocrystalline grains were about 20 nm and 10²³–10²⁴ m⁻³, respectively. The saturation magnetic flux density B_s for the present alloy is more than 1.8 T, that is about 10% larger than that of Fe-based amorphous alloys. Moreover, core loss P of the present alloy is about half of that of Si-steel up to B=1.7 T.     

Magnetic after-effect in Ni–Mn–Sb Heusler alloy

The ferromagnetic Heusler-type alloy _Ni50Mn35Sb15${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{35}{\mathrm{Sb}}_{15}$ exhibits well defined shape memory behaviour. We have investigated the transport and magnetic properties of this alloy across the martensitic transformation. Pronounced thermo-magnetic irreversibility between zero-field-cooled and field-cooled susceptibility data was observed below the martensitic transition temperature. We observe significant magnetic after-effect in magnetisation in both austenite and martensitic phases. However, a clear change in the nature of relaxation is observed as the sample is cooled across the martensitic transition temperature. These observations can be explained on the basis of complex domain dynamics in presence of rich micro-structure formation in the martensite.     

Preparation and magnetic properties of Fe–Ag granular alloy

An aqueous solution of AgNO₃ in the presence of ammonia and Fe(CO)₅ is sonicated under a H₂/Ar mixture, yielding a nanostructured homogeneous phase of Ag/Fe₂O₃. This composite material is further reduced at 300°C under hydrogen to produce the nanophased Fe/Ag solid mixture. The as-prepared material, as well as the reduced mixture, is analyzed by various conventional methods. Magnetization loops, ESR, Mössbauer, and magnetoresistance measurements are also conducted to determine the magnetic properties of the products.     

Formation and crystallization kinetics of Nd–Fe–B-based bulk amorphous alloy

In order to improve the glass-forming ability (GFA) of Nd–Fe–B ternary alloys to obtain fully amorphous bulk Nd–Fe–B-based alloy, the effects of Mo and Y doping on GFA of the alloys were investigated. It was found that the substitution of Mo for Fe and Y for Nd enhanced the GFA of the Nd–Y–Fe–Mo–B alloys. It was also revealed that the GFA of the samples was optimized by 4 at.% Mo doping and increased with the Y content. The fully amorphous structures were all formed in the Nd $_{6-{x}}$ Y $_{{x}}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ (x $=$ 1–5) alloy rods with 1.5 mm-diameter. After subsequent crystallization, the devitrified Nd $_{3}$ Y $_{3}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ alloy rod exhibited a uniform distribution of grains with a coercivity of 364.1 kA/m. The crystallization behavior of Nd $_{3}$ Y $_{3}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ BMG was investigated in isothermal situation. The Avrami exponent n determined by JAM plot is lower than 2.5, implying that the crystallization is mainly governed by a growth of particles with decreasing nucleation rate.     

Synthesis,structure stability and magnetic properties of nanocrystalline Ag–Ni alloy

Silver–nickel alloy nanoparticles with an average size of 30–40 nm were synthesized by chemically reducing the mixture of silver and nickel salts using sodium borohydride. The structure and the magnetic properties of the alloy samples with different compositions were investigated. The phase stability of the material was analysed after annealing the sample in vacuum at various temperatures. The material exhibits single fcc phase which is stable up to 400 °C and Ni precipitation sets in when the sample is annealed to 500 °C. The thermal analysis using DSC was carried out to confirm the same. The alloy compositions are found to be in close correlation with the metal salt ratios in the precursors. The synthesized samples exhibit weak paramagnetic to ferromagnetic behaviour. The magnetic measurements reveal that by adjusting the precursor ratio, the Ni content in the material can be altered and hence its magnetic properties tailored to suit specific requirements. The formation of Ag–Ni alloy is confirmed by the observed Curie temperature from the magneto thermogram. Annealing the sample helps to produce significant enhancement in the magnetization of the material.     

Effect of Sn and Al additions on the microstructure and mechanical properties of amorphous Ti–Cu–Zr–Ni alloys

Amorphous Ti–Cu–Zr–Ni alloys with minor addition of Sn and Al were prepared by melt spinning technique.The effects of Sn and Al additions on the microstructures and mechanical properties of glassy ribbons were investigated.The amorphous state of ribbons was confirmed by x-ray diffraction and transmission electron microscopy,where those ribbons with Sn addition exhibited a fully amorphous state.The characteristic temperature indicates that Ti_(45)Cu_(35)Zr_(10)Ni_5Sn_5 alloy has a stronger glass-forming ability,as proven by differential scanning calorimetry.Ti_(45)Cu_(35)Zr_(10)Ni_5Al_5 alloy showed a better hardness of 9.23 GPa and elastic modulus of 127.15 GPa and good wear resistance.Ti_(45)Cu_(35)Zr_(10)Ni_5Sn_5 alloy displayed a pop-in event related to discrete plasticity according to nanoindentation.When the temperature is below 560 K,Ti_(45)Cu_(35)Zr_(10)Ni_5Sn_5 alloy mainly exhibits elasticity.When the temperature rises between 717 K and 743 K,it shows a significant increase in elasticity but decrease in viscoelasticity after the ribbon experiences the main relaxation at 717 K.When the temperature is above 743 K,the ribbon shows viscoplasticity.     

Hysteresis of nanocrystalline R–Fe–B

The energetic model of ferromagnetic hysteresis calculates the magnetic state of materials by minimizing the total energy function for statistical domain behavior. The approach shows good agreement with the magnetization curves of mechanically alloyed Pr₉Fe₈₅B₆ powder, heat treated at different temperatures.     

Microstructural investigation of Fe–Zr–B–Ag soft magnetic thin films

A microstructural study of DC-sputtered Fe_93−xZr₃B₄Ag_x films on Si(0 0 1) substrates has been carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). All samples were deposited as a function of additive Ag content (x=0–6 at%), and annealed in the range of temperature, 300–600°C, for 1 h in order to obtain enhanced soft magnetic properties. Through XRD and TEM investigation, Ag-free Fe₉₃Zr₃B₄ films on Si(0 0 1) substrates consisted of nano-crystalline Fe-based phases. In the presence of Ag additive element, the microstructure of as-deposited Fe_93−xZr₃B₄Ag_x films consisted of a mixture of majority of Fe-based amorphous and Ag crystalline phases. In this case, additive element, Ag played a role in retarding the formation of Fe-based crystalline phases during deposition, and insoluble nano-crystalline Ag particles were dispersed in the Fe-based amorphous matrix. As the content of Ag increased, the intensity of Ag crystalline XRD peak increased. Crystallization of Fe-based amorphous phase in the matrix of Fe₈₈Zr₃B₄Ag₅ thin films occurred at an annealing temperature of 400°C. In the case of Fe₈₈Zr₃B₄Ag₅ films annealed at 500°C, a much enhanced permeability of the Fe-based alloy thin films associated with nano-crystalline phases was achieved.     

Correlation between mechanical,thermal and electronic properties in Zr–Ni,Cu amorphous alloys

We show that mechanical properties (stiffness and hardness) of Zr–Ni, Cu amorphous alloys increase linearly with Ni, Cu content over a wide composition range (22?≤?x _Ni,Cu?≤?65 at%). This correlates with the observed increase in the Debye temperatures and densities with x and shows that the strength of interatomic bonding increases with x in these alloys. Accordingly, the thermal stability (e.g. the crystallization and glass transition temperatures) of these alloys also increases with x. Since the electronic density of states at the Fermi level decreases linearly with x within the same x-range, a very simple relationship exists between the electronic structure and mechanical and thermal properties. We also deduce the mechanical properties of hypothetic amorphous Zr and briefly discuss the possibility of its preparation.