15 research outputs found
Nitrogen-Based Magneto-Ionic Manipulation of Exchange Bias in CoFe/MnN Heterostructures
Electric field control of the exchange bias effect across
ferromagnet/antiferromagnet (FM/AF) interfaces has offered exciting potentials
for low-energy-dissipation spintronics. In particular, the solid state
magneto-ionic means is highly appealing as it may allow reconfigurable
electronics by transforming the all-important FM/AF interfaces through ionic
migration. In this work, we demonstrate an approach that combines the
chemically induced magneto-ionic effect with the electric field driving of
nitrogen in the Ta/CoFe/MnN/Ta structure to electrically
manipulate exchange bias. Upon field-cooling the heterostructure, ionic
diffusion of nitrogen from MnN into the Ta layers occurs. A significant
exchange bias of 618 Oe at 300 K and 1484 Oe at 10 K is observed, which can be
further enhanced after a voltage conditioning by 5% and 19%, respectively. This
enhancement can be reversed by voltage conditioning with an opposite polarity.
Nitrogen migration within the MnN layer and into the Ta capping layer cause the
enhancement in exchange bias, which is observed in polarized neutron
reflectometry studies. These results demonstrate an effective nitrogen-ion
based magneto-ionic manipulation of exchange bias in solid-state devices.Comment: 28 pages, 4 figures; supporting information: 17 pages, 11 figure
Emergent electric field control of phase transformation in oxide superlattices.
Electric fields can transform materials with respect to their structure and properties, enabling various applications ranging from batteries to spintronics. Recently electrolytic gating, which can generate large electric fields and voltage-driven ion transfer, has been identified as a powerful means to achieve electric-field-controlled phase transformations. The class of transition metal oxides provide many potential candidates that present a strong response under electrolytic gating. However, very few show a reversible structural transformation at room-temperature. Here, we report the realization of a digitally synthesized transition metal oxide that shows a reversible, electric-field-controlled transformation between distinct crystalline phases at room-temperature. In superlattices comprised of alternating one-unit-cell of SrIrO3 and La0.2Sr0.8MnO3, we find a reversible phase transformation with a 7% lattice change and dramatic modulation in chemical, electronic, magnetic and optical properties, mediated by the reversible transfer of oxygen and hydrogen ions. Strikingly, this phase transformation is absent in the constituent oxides, solid solutions and larger period superlattices. Our findings open up this class of materials for voltage-controlled functionality
Tekućinski antisolvent postupak taloženja za modifikaciju topljivosti bikalutamida
Liquid antisolvent process was explored as a solubility modulating tool. Bicalutamide, a poorly water soluble drug, was used as a candidate. Low aqueous solubility and poor dissolution of bicalutamide results into poor and variable bioavailability. Therefore, the objective of the present work was to modify the solubility of bicalutamide using the liquid antisolvent precipitation process. HPMC E5 and Poloxamer 407 were shortlisted as a hydrophilic polymer and surfactant, respectively, for the process. Process optimization was done with respect to the hydrophilic polymer, surfactant and drug loading concentration. The resultant microcrystals were characterized with various instrumental techniques for material characterization such as IR, DSC, SEM, XRD, particle size, specific surface area and dissolution kinetics.Tekućinski antisolvent postupak upotrijebljen je za moduliranje topljivosti bikalutamida. Zbog vrlo slabe topljivosti u vodi i sporog oslobađanja, bioraspoloživost bikalutamida je mala i varijabilna. Cilj rada je poboljšati topljivost bikalutamida koristeći antisolvent precipitaciju. Kao hidrofilni polimer korišten je HPMC E5, a kao surfaktant Poloxamer 407. Variranjem količine polimera, surfaktanta i lijeka proces je optimiran. Nastali mikrokristali analizirani su uobičajenim instrumentalnim tehnikama za karakterizaciju materijala kao što su IR, DSC, SEM, XRD, veličina čestica, specifična površina i brzina oslobađanja
Magnetic field-induced non-trivial electronic topology in Fe3−xGeTe2
The anomalous Hall, Nernst and thermal Hall coefficients of
FeGeTe display several features upon cooling, like a reversal in
the Nernst signal below K pointing to a topological transition (TT)
associated to the development of magnetic spin textures. Since the anomalous
transport variables are related to the Berry curvature, a possible TT might
imply deviations from the Wiedemann-Franz (WF) law. However, the anomalous Hall
and thermal Hall coefficients of FeGeTe are found, within our
experimental accuracy, to satisfy the WF law for magnetic-fields
applied along its inter-layer direction. Surprisingly, large anomalous
transport coefficients are also observed for applied along the planar
\emph{a}-axis as well as along the gradient of the chemical potential, a
configuration that should not lead to their observation due to the absence of
Lorentz force. However, as \emph{a}-axis is increased,
magnetization and neutron scattering indicate just the progressive canting of
the magnetic moments towards the planes followed by their saturation. These
anomalous planar quantities are found to not scale with the component of the
planar magnetization (), showing instead a sharp decrease beyond 4 T which is the field required to align the magnetic moments
along . We argue that locally chiral spin structures, such as
skyrmions, and possibly skyrmion tubes, lead to a field dependent
spin-chirality and hence to a novel type of topological anomalous transport.
Locally chiral spin-structures are captured by our Monte-Carlo simulations
incorporating small Dzyaloshinskii-Moriya and biquadratic exchange
interactions.Comment: 34 pages, 10 figures, submitted to Applied Physics Review
Metallicity in SrTiO3 substrates induced by pulsed laser deposition
Oxygen deficiency has been known to induce metallic conduction in bulk and thin film SrTiO3 (STO). Here, we report on the metallicity of STO substrates induced by the pulsed laser deposition (PLD) process of STO films under various oxygen-poor growth conditions. Depositions as short as 2 min result in conduction through the STO substrate. Films grown on other substrates are insulating, and STO substrates annealed under the same growth conditions without laser ablation remain insulating. By varying background gas composition during deposition, we find that the transport behavior transitions from metallic to insulating behavior at progressively higher ambient pressures for O2, 99% N2/1% O2, N2, and Ar. Metallic behavior persists to deposition pressures as high as 10−2 Torr in Ar. These results suggest that, during the PLD process, the deposition kinetics and plume energy are a dominant factor in the formation of oxygen vacancies which then diffuse into the substrate. Understanding these mechanisms is crucial to prevent STO substrate reduction during PLD of films which require low O2 partial pressures during growth
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Nitrogen-Based Magneto-ionic Manipulation of Exchange Bias in CoFe/MnN Heterostructures
Electric field control of the exchange bias effect across ferromagnet/antiferromagnet (FM/AF) interfaces has offered exciting potentials for low-energy-dissipation spintronics. In particular, the solid-state magneto-ionic means is highly appealing as it may allow reconfigurable electronics by transforming the all-important FM/AF interfaces through ionic migration. In this work, we demonstrate an approach that combines the chemically induced magneto-ionic effect with the electric field driving of nitrogen in the Ta/Co0.7Fe0.3/MnN/Ta structure to electrically manipulate exchange bias. Upon field-cooling the heterostructure, ionic diffusion of nitrogen from MnN into the Ta layers occurs. A significant exchange bias of 618 Oe at 300 K and 1484 Oe at 10 K is observed, which can be further enhanced after a voltage conditioning by 5 and 19%, respectively. This enhancement can be reversed by voltage conditioning with an opposite polarity. Nitrogen migration within the MnN layer and into the Ta capping layer cause the enhancement in exchange bias, which is observed in polarized neutron reflectometry studies. These results demonstrate an effective nitrogen-ion based magneto-ionic manipulation of exchange bias in solid-state devices
Emergent Ferromagnetism in CaRuO<sub>3</sub>/CaMnO<sub>3</sub> (111)-Oriented Superlattices
The boundary between CaRuO3 and CaMnO3 is
an ideal test bed for emergent magnetic ground states stabilized through
interfacial electron interactions. In this system, nominally antiferromagnetic
and paramagnetic materials combine to yield interfacial ferromagnetism
in CaMnO3 due to electron leakage across the interface.
In this work, we show that the crystal symmetry at the surface is
a critical factor determining the nature of the interfacial interactions.
Specifically, by growing CaRuO3/CaMnO3 heterostructures
along the (111) instead of the (001) crystallographic axis, we achieve
a 3-fold enhancement of the magnetization and involve the CaRuO3 layers in the ferromagnetism, which now spans both constituent
materials. The stabilization of a net magnetic moment in CaRuO3 through strain effects has been long-sought but never consistently
achieved, and our observations demonstrate the importance of interface
engineering in the development of new functional heterostructures
Exchange-biased quantum anomalous Hall effect
The quantum anomalous Hall (QAH) effect is characterized by a dissipationless
chiral edge state with a quantized Hall resistance at zero magnetic field.
Manipulating the QAH state is of great importance in both the understanding of
topological quantum physics and the implementation of dissipationless
electronics. Here, we realized the QAH effect in the magnetic topological
insulator Cr-doped (Bi,Sb)2Te3 (CBST) grown on an uncompensated
antiferromagnetic insulator Al-doped Cr2O3. Through polarized neutron
reflectometry (PNR), we find a strong exchange coupling between CBST and
Al-Cr2O3 surface spins fixing interfacial magnetic moments perpendicular to the
film plane. The interfacial coupling results in an exchange-biased QAH effect.
We further demonstrate that the magnitude and sign of the exchange bias can be
effectively controlled using a field training process to set the magnetization
of the Al-Cr2O3 layer. Our work demonstrates the use of the exchange bias
effect to effectively manipulate the QAH state, opening new possibilities in
QAH-based spintronics
Reduction-Induced Magnetic Behavior in LaFeO<sub>3−δ</sub> Thin Films
The effect of oxygen reduction on the magnetic properties of LaFeO3−δ (LFO) thin films was studied to better understand the viability of LFO as a candidate for magnetoionic memory. Differences in the amount of oxygen lost by LFO and its magnetic behavior were observed in nominally identical LFO films grown on substrates prepared using different common methods. In an LFO film grown on as-received SrTiO3 (STO) substrate, the original perovskite film structure was preserved following reduction, and remnant magnetization was only seen at low temperatures. In a LFO film grown on annealed STO, the LFO lost significantly more oxygen and the microstructure decomposed into La- and Fe-rich regions with remnant magnetization that persisted up to room temperature. These results demonstrate an ability to access multiple, distinct magnetic states via oxygen reduction in the same starting material and suggest LFO may be a suitable materials platform for nonvolatile multistate memory