18 research outputs found
Playing with universality classes of Barkhausen avalanches
Many systems crackle, from earthquakes and financial market to Barkhausen
effect in ferromagnetic materials. Despite the diversity in essence, the noise
emitted in these dynamical systems consists of avalanche-like events with broad
range of sizes and durations, characterized by power-law avalanche
distributions and typical average avalanche shape that are signatures dependent
on the universality class of the underlying dynamics. Here we focus on the
crackling noise in ferromagnets and scrutinize the traditional statistics of
Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films
having different thicknesses. We show how scaling exponents and average shape
of the avalanches evolve with the structural character of the materials and
film thickness. We find quantitative agreement between experiment and
theoretical predictions of models for the magnetic domain wall dynamics, and
then elucidate the universality classes of Barkhausen avalanches in
ferromagnetic films. Thereby, we observe for the first time the dimensional
crossover in the domain wall dynamics, and the outcomes of the interplay
between system dimensionality and range of interactions governing the domain
wall dynamics on Barkhausen avalanches.Comment: 6 figures, 2 table
Tailoring of magnetocaloric effect in Ni45.5Mn43.0In11.5 metamagnetic shape memory alloy
We investigate the direct and inverse magnetocaloric effect in Ni45.5Mn43.0In11.5 Heusler alloy ribbons comparing the results obtained for the as-quenched sample with the ones after different annealing procedures. An enhancement and shift of the entropy maximum to near room temperature is observed in all annealed samples. A remarkable magnetocaloric effect is observed in samples with short-time treatment (10 minutes) and at the lowest annealing temperature. We show that the suppressing of uncompensated martensitic transition and thermal hysteresis are both influenced by the heat treatment. Also, an improvement on Curie’s temperature is observed and, at low magnetic field, it has been risen up to 310 K. Our results demonstrate that the martensitic transformation is highly sensitive to the applied magnetic field and also to the annealing treatment, which means that the magnetocaloric effect can be tuned showing different behaviors for each sample.Authors are thankful to Spanish MICINN for financial support: MAT2009-13108-C02-01-02 and MAT2010-20798-C05-04. L. Gonzalez also thanks MICINN for a FPI Grant and J. GarcĂa FICYT for a “Severo Ochoa” Grant
Stress level in finemet materials studied by impedanciometry
In this work, a study of the stress relief in Finemet ribbons, Fe73.5Cu1Nb3Si16.5B6, as a function of the annealing temperature is presented. The as melt-spun samples are amorphous and become partially crystallized after annealing at appropriate temperatures. For temperatures TA≥480°C the samples are nanocrystalline, with a microstructure composed by α-Fe12xSix(x~0.2) crystallites (10 nm average diameter) embedded in an amorphous matrix. Nanocrystallization, associated with stress relief effects, improves the soft magnetic properties of this kind of material. The stress level was quantified using magnetorestriction (measured by SAMR), magnetoelastic anisotropy, and domain wall energy data obtained from impedance spectra measurements. A reduction of the internal stress from 15 to 0.2 MPa was verified when comparing the as-cast to the sample annealed at 580°C. Improvement of the magnetic softness of the samples was also followed by the increase of the domain wall and magnetization rotation contributions to the overall effective permeability
Stress level in finemet materials studied by impedanciometry
In this work, a study of the stress relief in Finemet ribbons, Fe73.5Cu1Nb3Si16.5B6, as a function of the annealing temperature is presented. The as melt-spun samples are amorphous and become partially crystallized after annealing at appropriate temperatures. For temperatures TA≥480°C the samples are nanocrystalline, with a microstructure composed by α-Fe12xSix(x~0.2) crystallites (10 nm average diameter) embedded in an amorphous matrix. Nanocrystallization, associated with stress relief effects, improves the soft magnetic properties of this kind of material. The stress level was quantified using magnetorestriction (measured by SAMR), magnetoelastic anisotropy, and domain wall energy data obtained from impedance spectra measurements. A reduction of the internal stress from 15 to 0.2 MPa was verified when comparing the as-cast to the sample annealed at 580°C. Improvement of the magnetic softness of the samples was also followed by the increase of the domain wall and magnetization rotation contributions to the overall effective permeability
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In this work, the magnetization dynamics of soft magnetic materials is studied with the aid of transverse differential permeability ÎĽ(Iac , f ,Hdc) spectra. Contributions to the magnetization processes from domain wall motion and rotation of the magnetization can be extracted from the transverse differential permeability data which are in turn obtained from impedance Z(Iac , f ,Hdc) spectra. In particular, an iteration method is used to extract ÎĽ(Iac , f ,Hdc) from Z(Iac , f ,Hdc) data. The approach is tested in samples with a very well known domain structure, namely (110)[[001]FeSi3%. Permeability spectra ÎĽ(Iac , f ,Hdc) were obtained in the frequency range (100 Hz<f<=100 <=kHz), probe current range (0.1<Iac<50 mA) and dc magnetizing field range (0<=Hdc<=500 Oe). It is shown that the method developed in this article can be efficiently used to identify and study different dynamic processes driven by the probe current and controlled by the external dc field. In particular, it is shown that the method provides the tools to separate the reversible and irreversible parts of these processes
Barkhausen noise in the reentrant system Ni(1-X) Mn(x) : a study of the power spectra
In this article, the power spectra of the Barkhausen noise of Ni1-x Mnx is presented. The measurements were made in the ferromagnetic phase at several temperatures and manganese concentrations in order to map the effects of the degree of disorder and of the temperature on domain wall dynamics. Measurements in standard ferromagnetic materials were also made to compare the dynamics in both cases
Barkhausen noise in the reentrant system Ni(1-X) Mn(x) : a study of the power spectra
In this article, the power spectra of the Barkhausen noise of Ni1-x Mnx is presented. The measurements were made in the ferromagnetic phase at several temperatures and manganese concentrations in order to map the effects of the degree of disorder and of the temperature on domain wall dynamics. Measurements in standard ferromagnetic materials were also made to compare the dynamics in both cases