6 research outputs found
Experimental determination of the magnetization dependent part of the demagnetizing field in hard magnetic materials
International audienceA method for extracting the magnetization dependent part of the demagnetizing field from minor hysteresis loops is described. It applies to hard magnetic materials with irreversible magnetization switching. The method's validity is tested on the simulated magnetization curves of an assembly of hard magnetic grains, as well as on a thin NdFeB film with out of plane magnetization. Effective demagnetization factors are extracted from the analysis. These factors are smaller than the usually applied sample shape dependent demagnetizing factors
Electric-Field Induced Reversible Switching of the Magnetic Easy Axis in Co/BiFeO3 on SrTiO3
Self-Assembly with Orthogonal-Imposed Stimuli To Impart Structure and Confer Magnetic Function To Electrodeposited Hydrogels
A magnetic nanocomposite film with
the capability of reversibly collecting functionalized magnetic particles
was fabricated by simultaneously imposing two orthogonal stimuli (electrical
and magnetic). We demonstrate that cathodic codeposition of chitosan
and Fe<sub>3</sub>O<sub>4</sub> nanoparticles while simultaneously
applying a magnetic field during codeposition can (i) organize structure,
(ii) confer magnetic properties, and (iii) yield magnetic films that
can perform reversible collection/assembly functions. The magnetic
field triggered the self-assembly of Fe<sub>3</sub>O<sub>4</sub> nanoparticles
into hierarchical “chains” and “fibers”
in the chitosan film. For controlled magnetic properties, the Fe<sub>3</sub>O<sub>4</sub>-chitosan film was electrodeposited in the presence
of various strength magnetic fields and different deposition times.
The magnetic properties of the resulting films should enable broad
applications in complex devices. As a proof of concept, we demonstrate
the reversible capture and release of green fluorescent protein (EGFP)-conjugated
magnetic microparticles by the magnetic chitosan film. Moreover, antibody-functionalized
magnetic microparticles were applied to capture cells from a sample,
and these cells were collected, analyzed, and released by the magnetic
chitosan film, paving the way for applications such as reusable biosensor
interfaces (e.g., for pathogen detection). To our knowledge, this
is the first report to apply a magnetic field during the electrodeposition
of a hydrogel to generate magnetic soft matter. Importantly, the simple,
rapid, and reagentless fabrication methodologies demonstrated here
are valuable features for creating a magnetic device interface
Electric-Field Induced Reversible Switching of the Magnetic Easy Axis in Co/BiFeO<sub>3</sub> on SrTiO<sub>3</sub>
Electric-field
(E-field) control of magnetism
enabled by multiferroic materials has the potential to revolutionize
the landscape of present memory devices plagued with high energy dissipation.
To date, this <i>E</i>-field controlled multiferroic scheme
has only been demonstrated at room temperature using BiFeO<sub>3</sub> films grown on DyScO<sub>3</sub>, a unique and expensive substrate,
which gives rise to a particular ferroelectric domain pattern in BiFeO<sub>3</sub>. Here, we demonstrate reversible electric-field-induced switching
of the magnetic state of the Co layer in Co/BiFeO<sub>3</sub> (BFO)
(001) thin film heterostructures fabricated on (001) SrTiO<sub>3</sub> (STO) substrates. The angular dependence of the coercivity and the
remanent magnetization of the Co layer indicates that its easy axis
reversibly switches back and forth 45° between the (100) and
the (110) crystallographic directions of STO as a result of alternating
application of positive and negative voltage pulses between the patterned
top Co electrode layer and the (001) SrRuO<sub>3</sub> (SRO) layer
on which the ferroelectric BFO is epitaxially grown. The coercivity
(H<sub>C</sub>) of the Co layer exhibits a hysteretic behavior between
two states as a function of voltage. A mechanism based on the intrinsic
magnetoelectric coupling in multiferroic BFO involving projection
of antiferromagnetic G-type domains is used to explain the observation.
We have also measured the exact canting angle of the G-type domain
in strained BFO films for the first time using neutron diffraction.
These results suggest a pathway to integrating BFO-based devices on
Si wafers for implementing low power consumption and nonvolatile magnetoelectronic
devices