Department of Physics

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Crystallization behavior and magnetic properties of rapidly solidified Fe73.5Nb3Si13.5B9 alloys were studied with 1 at .% Cu or Mn or Pt as the fifth alloying element. Crystallization behavior was investigated by electrical resistivity and differential scanning calorimetry techniques. Addition of Mn or Pt enhanced the temperature coefficient of resistivity. A two stage crystallization process was observed in Cu-containing alloys whereas the Mn- and Pt-containing alloys exhibited three-stage processes. A broad exothermic maximum with the onset at 808 K, which is characteristic of the formation of Fe3Si nanoparticles was observed only in Cu-containing samples. The formation of various intermetallic phases along with the Fe3Si nanoparticles in annealed Mn and Pt systems made these two alloys magnetically inferior compared to the Cu-containing alloy. © 2001 Elsevier Science B.V. All rights reserved.

World University root node

Materials Science and Engineering A

Crystallization and magnetic properties of rapidly solidified Fe-Nb-M-Si-B (M = Cu, Mn, Pt)

An astonishing new phenomenon has been recently observed in magnetic wires. It consists of the spontaneous rotation of the wires when submitted to an exciting AC axial field with frequency of the order of kHz and amplitude above some threshold. The rotation is believed to appear due to interaction between generated magnetoelastic standing waves and induced eddy currents. In the present work rotational characteristics of Fe77.5Si7.5B15 and Fe73.5Si13.5B9Cu1Nb3 wires in their as-cast amorphous state and after heat treatments leading to devitrification has been investigated. It is proved that this rotational phenomenon is only observed in samples with large enough magnetostriction irrespective of their structural character. Moreover, changes in rotational characteristics are ascribed to the structural modifications accompanying the devitrification process.

Materials Research Society Symposium - Proceedings

Spontaneous AC field induced mechanical rotation in magnetostrictive FeSiB-based wires subjected to thermal treatments

Amorphous ribbons of composition technique. A convergent nozzle of suitable dimensions was chosen so as to minimise the turbulent flow of the fluid. The separation between the nozzle and the quenching wheel surface was kept constant at 0.5 mm. The quenching rate was directly proportional to the wheel velocity as the dimension of the crucible and the position of crucible with respect to wheel surface were kept fixed in all the trials. The thickness of ribbon was found to decrease while the ductility increased with the increase of wheel surface velocity, i.e. with the increase of quenching rate. The amorphous to nanocrystalline transformation temperature was found to remain constant when the wheel surface velocity was more than 32 m/s and also the soft magnetic properties were found to be superior. © 2001 Elsevier Science B.V. All rights reserved.

Effect of quenching rate on the properties of melt-spun FeNbCuSIB ribbons

The novel effect consisting of the spontaneous mechanical rotation when subjected to axial high-frequency ac magnetic field is reported for Fe73.5Nb3Cu1Si13.5B9 amorphous as-cast wires and after devitrification. The rotation is observed at a spectrum of frequencies of the exciting applied field and as a consequence of the interaction of a generated magnetoelastic standing wave with an induced circular current. A correlation is found between complex spectra of rotational frequencies and the characteristics of the existing structural phases. Four characteristic frequencies and their harmonics are differentiated in the as-cast state. New rotational frequencies are observed at the very early stages of nanocrystallization, which can be ascribed to initial structural rearrangements. However, the spontaneous rotation vanishes in samples annealed at 550°C and 570°C where optimum ultra-soft magnetic behaviour is achieved and magnetostriction is drastically reduced. In this state, rotation is not observed as a consequence of the disappearance of the magnetoelastic wave because of the reduced magnetostriction. The rotation of the wire is observed again when annealed at 650°C, due to a final increase of magnetostriction upon further crystallisation of the system. The direct correlation between magnetostriction and the field-induced rotation of the wire is thus shown.

Journal of Physics D: Applied Physics

Spontaneous mechanical rotation of as-cast and annealed FeSiBNbCu wires under high-frequency axial ac field

The nanocrystalline state of Fe 73.5 Nb 3 Cu 1 Si 13.5 B 9 ribbons exhibit superior soft magnetic properties with low coercivity, high permeability and moderate saturation induction value. However, due to the metastable nature of the materials, their properties depend very much on the preparation condition and heat treatment schedule. In the present work, the properties of the as-cast ribbons prepared at different nozzle diameter and separation between the quenching wheel and the nozzle were evaluated. The optimum conditions for getting continuous long ribbon from 150g of ingot were established. The influence of heat treatment to get nanostructure and superior soft magnetic properties for selected ribbons were also studied. The ribbon surface quality was improved by reducing air pockets at the ribbon surface which was in contact with the quenching wheel. © 2001 Elsevier Science B.V. All rights reserved.

Applied Surface Science

Preparation and characterization of Fe-Nb-Cu-Si-B-based nanocrystalline soft magnetic materials

The magnetic and the structural properties have been investigated for Fe73.5Nb3M1Si13.5B9 (M = Cu, Mn, Pt) alloys in their as-received and heat-treated state. Differential scanning calorimeter and scanning electrical resistivity were used to study crystallization behaviour and to examine the influence of the nucleation elements Cu, Mn and Pt on the structural and magnetic properties of Fe-based nanocrystalline materials. The temperature coefficient of resistivity above Curie temperature was found to be very low (0.2×10-4 K-1) in the Cu containing alloy as compared to the alloys which contained Mn or Pt. A broad exothermic DSC peak for the formation of Fe3Si nanoparticles was absent when Cu was replaced by Mn or Pt. Instead, a sharp exothermic peak for the formation of Fe3(SiB) phase was observed with an onset at 875 K. The magnetic properties of the three alloys measured after stress relaxed annealing were similar. However, after first-stage crystallization, the soft magnetic properties were further enhanced only in Cu containing alloys due to the formation of Fe3Si nanoparticles. Such nanoparticles together with different intermetallic phases like FeMn3 or FePt3 were formed in Mn or Pt containing alloys. Moreover, the NbFeSi phase was also formed in the latter alloys after higher temperature annealing which reduced not only the amount of the Fe3Si phase but also the grain refining effect due to the lesser amount of Nb available at the grain boundary. When Cu was replaced by Mn or Pt, the formation of different intermetallics reduced the volume fraction of Fe3Si nanoparticles and the lesser amount of grain refining Nb made the materials magnetically inferior after annealing above 775 K.

Journal of Magnetism and Magnetic Materials

Structural and soft magnetic properties of Fe73.5Nb3M1Si13.5B9 (M = Cu, Mn, Pt)

We present the quantum theory of a Stern-Gerlach system in contact with a linearly dissipative environment at an arbitrary temperature. The dynamics of the reduced density matrix of the system is calculated using the path integral technique, under a general condition when the system and its environment may not be decoupled initially. We analyze the behavior of the density matrix in the long-time limit and compute the time scales of decay of the elements off-diagonal in the coordinate and the momentum space, for the cases of high temperature, zero temperature, and intermediate temperature baths. © 2000 The American Physical Society.

Physical Review A - Atomic, Molecular, and Optical Physics

Quantum theory of a Stern-Gerlach system in contact with a linearly dissipative environment

In this study, an attempt was made to solve the dynamics of the Stern-Gerlach spin in contact with a linearly dissipative environment at an arbitrary temperature. All the previous results in the high-temperature limit were recovered. It was observed that except for the extreme quantum case of zero temperature, the system shows the expected classical diffusive behavior over long times.

The laser produced carbon plasma in different regions of a curved magnetic field has been studied by emission spectroscopy. In addition to the ionic transitions CII, CIII, CIV; C2 Swan bands are observed. The intensity of the C2 Swan band is greatly enhanced when the magnetic field lines are convex to the moving plasma with the positive field gradient. The observed change in emission characteristics is attributed to the recombination of electrons due to the curvature gradient drift of the magnetic field. © 1999 Published by Elsevier Science B.V. All rights reserved.

Physics Letters, Section A: General, Atomic and Solid State Physics

Optical emission studies of laser ablated carbon plasma in a curved magnetic field

The magnetically bistable nature of as-quenched Fe77.5Si7.5B15 amorphous fibre disappeared when the material underwent stress-relief annealing at 400°C for 30 min. A reduction of internal stress leading to a lowering of the magnetoelastic anisotropy was the cause of such a change from bistable to normal ferromagnetic behaviour. Cathodic hydrogen impregnation caused the re-appearance of magnetic bistability, the magnitude of which was dependent on the duration of hydrogen charging (and hence on the hydrogen concentration). Perfect bistability was restored when the annealed Fe77.5Si7.5B15 fibre was charged for 120 min at the charging current density of 120 mA cm-2. Owing to the positive molar volume of hydrogen, internal stresses were generated by hydrogenation, which increased the size of the longitudinal anisotropy region. When this longitudinal anisotropy region was big enough to act as a monodomain at the core of the fibre, bistability with a large switching field (H* = 17.5 A m-1) was observed.