Uniaxial Garnet Films Research Articles

Magneto-Optic Fraunhofer Diffraction on 2D Magnetic Domain Patterns

Magneto-optical Fraunhofer diffraction on phase 2D domain patterns with Cmm6 and Pab2 symmetry in uniaxial iron garnet films was studied. Domain patterns contain more than 100 elementary cells and have high spatial homogeneity. The diffraction patterns contain up to 10 or more orders of peaks. Possibilities of space-time modulation of optical radiation and multiplication of the modulation frequency both under change of diffraction order as well as amplitude of magnetic bias field strength were shown.

Evidence of Rouse-like dynamics in magnetically ratchetting colloidal chains

We study the collective dynamics of an ensemble of paramagnetic particles organized as a 1D chain and driven by an a-thermal ratchet effect on a uniaxial garnet film. The centre of mass of the chain shows diffusive behavior with mean square displacement ∼t, while its end-to-end distance shows anomalous (sub-diffusive) kinetics growing as . We extract the potential of mean force between the particles within the chain by invoking the Pope–Ching equation. We interpret the experimental data using the Rouse model, originally developed for polymers, and experimentally extract all relevant parameters.

Hysteresis loop design by geometry of garnet film element with single domain wall

Numerical modeling and experimental investigation of magnetostatic stable states of two-domain structure in Bi-substituted uniaxial garnet film elements was made. Single domain walls (DW) between two opposite normally magnetized parts in isolated rectangular strip and strip-like bridge are found to exhibit different behavior. DW inside strip (bridge) suffers increasing repulsion (attraction) from nearest edge when shifted from element center. DW position center position is stable in isolated strip but bridge is magnetized spontaneously to one of two saturated states in zero external field. Isolated strip magnetization process occurs reversibly while bridge magnetization reversal occurs by coercive manner. Strip susceptibility and bridge coercive field are entirely defined by magnetostatic barrier created by element boundary stray field in case of constant DW length during magnetization reversal. Variation of strip and bridge boundary shape along DW trajectory gives the opportunity to create additional controllable potential profile due to DW surface energy modulation by DW length. Garnet elements with high Faraday rotation and low light switching field were developed for fine magnetic sensing and optical data processing applications.

Synchronization and Beating in Dipolarly Coupled Colloidal Rotators

One paramagnetic microsphere confined above a circular block wall in a uniaxial garnet film shows synchronous or asynchronous dynamics when subjected to an external rotating magnetic field. Here it is shown that in the bidisperse system a very rich behavior arises with synchronization, beating, and independent particle rotations. The beating dynamics, which allows generating two distinct rotation frequencies, is influenced by magnetic dipolar interactions between the circulating colloids. Numerical simulation supports the experimental data that demonstrate the importance of dipolar interactions in the beating dynamics.

Giant Transversal Particle Diffusion in a Longitudinal Magnetic Ratchet

We study the transversal motion of paramagnetic particles on a uniaxial garnet film, exhibiting a longitudinal ratchet effect in the presence of an oscillating magnetic field. Without the field, the thermal diffusion coefficient obtained by video microscopy is D(0) ≈ 3 × 10(-4) μm2/s. With the field, the transversal diffusion exhibits a giant enhancement by almost four decades and a pronounced maximum as a function of the driving frequency. We explain the experimental findings with a theoretical interpretation in terms of random disorder effects within the magnetic film.

DYNAMICS OF A CLASSICAL PARTICLE EXTERNALLY DRIVEN ON A MAGNETIC BUBBLE LATTICE

We study the motion of a classical paramagnetic particle externally driven above a hexagonal lattice of ferromagnetic bubbles. The presented simulations reproduce recently observed trajectories of micron-size colloidal particles externally driven above a uniaxial garnet film [Tierno et al., 2007a].

Dynamic colloidal sorting on a magnetic bubble lattice

We use a uniaxial garnet film with a magnetic bubble lattice to sort paramagnetic colloidal particles with different diameters, i.e., 1.0 and 2.8μm. We apply an external magnetic field which precesses around an axis normal to the film with a frequency Ω=62.8s−1 and intensity 3120A∕m <H<6911A∕m. By varying the component of the field Hz normal to the film, we observe that particles of one size are localized around magnetic bubbles while the others are transported through the array. We complement the experimental measurements with numerical simulations to explore the sorting capability for particles with different magnetic moments.

Localized and Delocalized Motion of Colloidal Particles on a Magnetic Bubble Lattice

We study the motion of paramagnetic colloidal particles placed above magnetic bubble domains of a uniaxial garnet film and driven through the lattice by external magnetic field modulation. An external tunable precessing field propels the particles either in localized orbits around the bubbles or in superdiffusive or ballistic motion through the bubble array. This motion results from the interplay between the driving rotating signal, the viscous drag force and the periodic magnetic energy landscape. We explain the transition in terms of the incommensurability between the transit frequency of the particle through a unit cell and the modulation frequency. Ballistic motion dynamically breaks the symmetry of the array and the phase locked particles follow one of the six crystal directions.

Barkhausen statistics from a single domain wall in thin films studied with ballistic Hall magnetometry

The movement of a micron-size section of an individual domain wall in a uniaxial garnet film was studied using ballistic Hall micromagnetometry. The wall propagated in characteristic Barkhausen jumps, with the distribution in jump size $S$, following the power-law relation, $D(S)\ensuremath{\propto}{S}^{\ensuremath{-}\ensuremath{\tau}}$. In addition to reporting on the suitability of employing this alternative technique, we discuss the measurements taken of the scaling exponent $\ensuremath{\tau}$, for a single domain wall in a two-dimensional sample with magnetization perpendicular to the surface, and low pinning center concentration. This exponent was found to be $1.14\ifmmode\pm\else\textpm\fi{}0.05$ at both liquid helium and liquid nitrogen temperatures.

Barkhausen effect in a garnet film studied by ballistic hall micromagnetometry

The movement of a micrometer-size section of a single domain wall in a uniaxial garnet film was studied using a ballistic Hall micromagnetometer at 77 K and 4.2 K. The wall propagated in characteristic Barkhausen jumps, with the jump size distribution following the power-law relation, P(S) ∝ S−τ. The scaling exponent, τ, was measured as 1.14 ± 0.05 at both temperatures. This is the first measurement of this exponent using such a device, and the first for a single wall in a two-dimensional sample with a low concentration of pinning centres, in which the magnetization of the sample is perpendicular to the surface.

Microscopic view on a single domain wall moving through ups and downs of an atomic washboard potential

Propagation of ferromagnetic domain walls on sub-atomic scale was measured in a thin uniaxial garnet film by using ballistic Hall magnetometry. Domain walls are found to move by equidistant steps, which correspond to the crystal lattice constant in this material. Our results are in good agreement with the theory of intrinsic pinning of a domain wall in the Peierls potential. We have also measured AC susceptibility of a domain wall moving inside a Peierls valley. The observed nonlinear behavior of the AC susceptibility can be understood within the framework of kinks and breathers nucleating and spreading along the domain wall.

COERCIVITY OF SINGLE PINNING CENTER MEASURED BY HALL MICROMAGNETOMETRY

Nanometer-scale movements of domain walls in uniaxial garnet films have been studied by means of micromagnetization measurements using miniature gold and semiconductor Hall probes. At helium temperatures the domain walls are found to move by discrete jumps, which we attribute to pinning on isolated defects, and we were able to measure local hysteresis loops associated with pinning on individual pinning centers. The temperature dependence of the coercive field of a single pinning center allowed us to evaluate the characteristic energy and characteristic volume of the pinning center.

Faraday-effect optical current sensor with a garnet film/ring core in a transverse configuration.

A new scheme of the Faraday effectcurrent sensor of a magnetic ring-core type is reported. With this scheme a uniaxial magnetic garnet film is obliquely inserted into a very narrow gap in the ring core and a probe light beam is passed through the garnet film in the transverse direction to the core. It is experimentally demonstrated that this current sensor shows good sensitivity as well as good isolation from surrounding currents, particularly because of the very narrow core gap allowed. This transverse scheme is much simpler and less expensive than the known longitudinal scheme and can offer a practical optical current sensor of a ring-core type.

Domain wall propagation on nanometer scale: coercivity of a single pinning center

Nanometer-scale movements of domain walls in uniaxial garnet films have been studied by means of micromagnetization measurements using miniature gold and semiconductor Hall probes. The high spatial resolution is achieved due to low intrinsic noise of semiconductor ballistic Hall microprobes. At low (helium) temperatures, the domain walls are found to move by discrete jumps, which we attribute to pinning on isolated defects, and we were able to measure local hysteresis loops associated with pinning on individual pinning centers. The temperature dependence of the coercive field of a single pinning center allowed us to evaluate the characteristic energy and characteristic volume of the pinning center. At higher temperatures, the character of domain wall propagation changed, and walls were found to move not only by jumps between pinning centers but also via elastic bending.

Room-temperature scanning Hall probe microscope (RT-SHPM) imaging of garnet films using new high-performance InSb sensors

High-performance InSb micro-Hall sensors were fabricated by optical lithography and incorporated in a room-temperature scanning Hall probe microscope for imaging of localized magnetic fluctuations in close proximity to the surfaces of crystalline uniaxial garnet films. The room-temperature noise figure of the InSb sensors was 6-10 mG//spl radic/Hz, which is an order of magnitude. better than GaAs-AlGaAs two-dimensional electron gas sensors used to date.

Thermostability of amorphous bubble lattices in garnet films

It is experimentally shown that amorphous bubble lattices formed in thin uniaxial garnet films are more thermostable than regular or cluster bubble lattices. The obtained experimental results are explained within the framework of a thermodynamical approach using the concept of the domain chemical potential.

Magneto-optic magnetic field sensors based on uniaxial iron garnet films in optical waveguide geometry

Iron garnet films which exhibit perpendicular uniaxial magnetic anisotropy are promising materials for magnetooptic magnetic field sensing. In an optical waveguide geometry, these materials exhibit large values of saturation Faraday rotation which in turn produce high sensitivity. The domain structure of these films favors magnetization rotation as the primary magnetization process. This process is significantly faster than domain wall motion, which is the primary magnetization process in bulk iron garnet crystals. Data which confirm the high sensitivity and wideband frequency response of these materials are presented. One film exhibits a virtually flat frequency response from DC to at least 1 GHz. Potential problems with waveguide sensors, such as birefringence and optical coupling efficiency appear to be soluble. >

The Domain FMR excitations in Uniaxial Garnet Films in Fields Parallel to the Film

Etude de la resonance ferromagnetique du domaine dans ces films. Ce phenomene se revele influence de facon negligeable par la faible homogeneite du champ de qui indique une forte interaction d'echange a longue distance dans le materiau

Resonances and domain wall structure transformation in uniaxial garnet films in in-plane field

A new mode of domain wall resonance oscillations with the frequency going to zero when the horizontal Bloch lines (HBL) are generated has been found for the first time. Transformation of the spectrum branches of the modes with different polarization due to gyrotropy of Bloch line motion has been observed.

Measurement of Bloch line coercivity in uniaxial garnet films

The coercive field of vertical Bloch lines in several uniaxial garnet film samples has been measured by two different methods. With the first method, individual isolated Bloch lines in stripe-domain walls and their response to external magnetic fields are observed directly using a one-sided dark-field illumination technique. The second method detects Block line motion in bubble-domain walls photometrically. By measuring over an array of bubble domains, an average of the scatter of coercivity data is obtained. Experimental results are presented. >