83 research outputs found
Barkhausen noise in soft amorphous magnetic materials under applied stress
We report experimental measurements of Barkhausen noise on
Fe_{64}Co_{21}B_{15} amorphous alloy under tensile stress. We interpret the
scaling behavior of the noise distributions in terms of the depinning
transition of the domain walls. We show that stress induced anisotropy enhance
the effect of short-range elastic interactions that dominate over long-range
dipolar interactions. The universality class is thus different from the one
usually observed in Barkhausen noise measurements and is characterized by the
exponents \tau = 1.3 and \alpha = 1.5, for the decay of the distributions of
jump sizes and durations.Comment: 6 pages, 3 .eps figures. Submitted to the 43rd Magnetism and Magnetic
Materials Conference (J. Appl. Phys.
Hysteresis and noise in ferromagnetic materials with parallel domain walls
We investigate dynamic hysteresis and Barkhausen noise in ferromagnetic
materials with a huge number of parallel and rigid Bloch domain walls.
Considering a disordered ferromagnetic system with strong in-plane uniaxial
anisotropy and in-plane magnetization driven by an external magnetic field, we
calculate the equations of motion for a set of coupled domain walls,
considering the effects of the long-range dipolar interactions and disorder. We
derive analytically an expression for the magnetic susceptivity, related to the
effective demagnetizing factor, and show that it has a logarithmic dependence
on the number of domains. Next, we simulate the equations of motion and study
the effect of the external field frequency and the disorder on the hysteresis
and noise properties. The dynamic hysteresis is very well explained by means of
the loss separation theory.Comment: 13 pages, 11 figure
Universality classes and crossover scaling of Barkhausen noise in thin films
We study the dynamics of head-to-head domain walls separating in-plane
domains in a disordered ferromagnetic thin film. The competition between the
domain wall surface tension and dipolar interactions induces a crossover
between a rough domain wall phase at short length-scales and a large-scale
phase where the walls display a zigzag morphology. The two phases are
characterized by different critical exponents for Barkhausen avalanche dynamics
that are in quantitative agreement with experimental measurements on MnAs thin
films.Comment: 5 pages, 5 figure
The role of stationarity in magnetic crackling noise
We discuss the effect of the stationarity on the avalanche statistics of
Barkhuasen noise signals. We perform experimental measurements on a
FeB amorphous ribbon and compare the avalanche distributions
measured around the coercive field, where the signal is stationary, with those
sampled through the entire hysteresis loop. In the first case, we recover the
scaling exponents commonly observed in other amorphous materials (,
). while in the second the exponents are significantly larger
(, ). We provide a quantitative explanation of the
experimental results through a model for the depinning of a ferromagnetic
domain wall. The present analysis shed light on the unusually high values for
the Barkhausen noise exponents measured by Spasojevic et al. [Phys. Rev. E 54
2531 (1996)].Comment: submitted to JSTAT. 11 pages 5 figure
The effect of disorder on transverse domain wall dynamics in magnetic nanostrips
We study the effect of disorder on the dynamics of a transverse domain wall
in ferromagnetic nanostrips, driven either by magnetic fields or spin-polarized
currents, by performing a large ensemble of GPU-accelerated micromagnetic
simulations. Disorder is modeled by including small, randomly distributed
non-magnetic voids in the system. Studying the domain wall velocity as a
function of the applied field and current density reveals fundamental
differences in the domain wall dynamics induced by these two modes of driving:
For the field-driven case, we identify two different domain wall pinning
mechanisms, operating below and above the Walker breakdown, respectively,
whereas for the current-driven case pinning is absent above the Walker
breakdown. Increasing the disorder strength induces a larger Walker breakdown
field and current, and leads to decreased and increased domain wall velocities
at the breakdown field and current, respectively. Furthermore, for adiabatic
spin transfer torque, the intrinsic pinning mechanism is found to be suppressed
by disorder. We explain these findings within the one-dimensional model in
terms of an effective damping parameter increasing with the disorder
strength.Comment: 5 pages, 3 figure
Loss separation for dynamic hysteresis in magnetic thin films
We develop a theory for dynamic hysteresis in ferromagnetic thin films, on
the basis of the phenomenological principle of loss separation. We observe
that, remarkably, the theory of loss separation, originally derived for bulk
metallic materials, is applicable to disordered magnetic systems under fairly
general conditions regardless of the particular damping mechanism. We confirm
our theory both by numerical simulations of a driven random--field Ising model,
and by re--examining several experimental data reported in the literature on
dynamic hysteresis in thin films. All the experiments examined and the
simulations find a natural interpretation in terms of loss separation. The
power losses dependence on the driving field rate predicted by our theory fits
satisfactorily all the data in the entire frequency range, thus reconciling the
apparent lack of universality observed in different materials.Comment: 4 pages, 6 figure
Collective Coordinate Descriptions of Magnetic Domain Wall Motion in Perpendicularly Magnetized Nanostructures under the Application of In-plane Fields
Manipulation of magnetic domain walls can be used to improve the capabilities
of the next generation of memory and sensing devices. Materials of recent
interest for such devices include heterostructures of ultrathin ferromagnets
sandwiched between a heavy metal and an oxide, where spin-orbit coupling and
broken inversion symmetry give rise to the Dzyaloshinskii-Moriya interaction
(DMI), stabilizing chiral domain walls. The efficiency of the motion of these
chiral domain walls may be controlled using in-plane magnetic fields. This
property has been used for measurement of DMI strength. While micromagnetic
simulations are able to accurately predict domain wall motion under in-plane
fields in these materials, collective coordinate models such as the
and models fail to reproduce the micromagnetic results. In this
theoretical work, we present a set of extended collective coordinate models
including canting in the domains, which better reproduce micromagnetic results,
and helps us better understand the effect of in-plane fields on magnetic domain
walls. These models are used in conjunction with micromagnetic simulations to
identify critical points observed in the motion of the domain walls driven by
out-of-plane magnetic fields, and electric current under magnetic in-plane
fields. Our new models and results help in the development of future domain
wall based devices based on perpendicularly magnetized materials
Collective coordinate descriptions of magnetic domain wall motion in perpendicularly magnetized nanostructures under the application of in-plane fields
Manipulation of magnetic domain walls in nanostructures can be used to improve the capabilities of the next generation of memory and sensing devices. Materials of interest for such devices include heterostructures of ultrathin ferromagnets sandwiched between a heavy metal and an oxide, where spin-orbit coupling and broken inversion symmetry give rise to the Dzyaloshinskii-Moriya interaction (DMI), stabilizing chiral domain walls. The efficiency of the motion of these chiral domain walls may be controlled using in-plane magnetic fields. This property has been used both for measurement of DMI strength, and for improved performance in applications. While micromagnetic simulations are able to accurately predict domain wall motion under in-plane fields in these materials, collective coordinate models such as the q-phi and q-phi-chi models fail to reproduce the micromagnetic results. In this theoretical work, we present a set of extended collective coordinate models including canting in the domains, which better reproduce micromagnetic results, and improve our understanding of the effect of in-plane fields on magnetic domain walls. These models are used in conjunction with micromagnetic simulations to develop simpler descriptions of DW motion under specific conditions. Our new models and results help in the development of future domain wall based devices based on perpendicularly magnetized materials.Comisión Europea (P7-PEOPLE-2013-ITN 608031)
Gobierno de España (MAT2014-52477-C5-4-P, MAT2017-87072-C4-1-P)
Junta de Castilla y Leon (SA090U16, SA282U14
Domain wall statics and dynamics in nanowires with arbitrary Dzyaloshinskii-Moriya tensors
The influence of different Dzyaloshinskii-Moriya interaction (DMI) tensor
components on the static and dynamic properties of domain walls (DWs) in
magnetic nanowires is investigated using one dimensional collective coordinates
models and micromagnetic simulations. It is shown how the different
contributions of the DMI can be compactly treated by separating the symmetric
traceless, antisymmetric and diagonal components of the DMI tensor. First, we
investigate the effect of all different DMI components on the static DW tilting
in the presence and absence of in plane (IP) fields. We discuss the
possibilities and limitations of this measurement approach for arbitrary DMI
tensors. Secondly, the interplay of different DMI tensor components and their
effect on the field driven dynamics of the DWs are studied and reveal a
non-trivial effect of the Walker breakdown field of the material. It is shown
how DMI tensors combining diagonal and off-diagonal elements can lead to a
non-linear enhancement of the Walker field, in contrast with the linear
enhancement obtainable in the usual cases (interface DMI or bulk DMI)
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