Inhomogeneous Magnetic Anisotropy in an FeGeTe Nanoflake Observed by Imaging.

Few-layer flakes of ferromagnetic FeGeTe with = 0.3 (F5GT) possess a -axis magnetocrystalline anisotropy that is large enough below ∼200 K to outcompete the easy-plane shape anisotropy, yielding distinctive magnetic microstructures with out-of-plane (OOP) magnetizations. Using photoemission electron microscopy (PEEM) with magnetic contrast from X-ray magnetic circular dichroism (XMCD) to study a thermally demagnetized h-BN-protected nanoflake of F5GT at 110 K, we observe a micron-scale coexistence between domains with OOP magnetizations (∼70% areal fraction) and hitherto unknown domains in which in-plane (IP) magnetization components dominate (∼30% areal fraction).

Developments in caloric measurements, materials, and devices at Calorics 2024.

Abstract: Heating and cooling combined constitute the world's largest form of end-use energy and the largest source of carbon emissions. It is therefore interesting to explore heat pumps based on caloric materials, which offer promising and environmentally friendly alternatives to gas combustion and vapor compression. The possibility of replacing these traditional methods of heating and cooling motivates the current research on caloric materials and devices.

Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer.

Topology created by quasi-continuous spatial variations of a local polarization direction represents an exotic state of matter, but field-driven manipulation has been hitherto limited to creation and destruction. Here we report that relatively small electric or mechanical fields can drive the non-volatile rotation of polar spirals in discretized microregions of the relaxor ferroelectric polymer poly(vinylidene fluoride-ran-trifluoroethylene). These polar spirals arise from the asymmetric Coulomb interaction between vertically aligned helical polymer chains, and can be rotated in-plane through various angles with robust retention.

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB.

Hydrostatic pressure represents an inexpensive and practical method of driving caloric effects in brittle magnetocaloric materials, which display first-order magnetostructural phase transitions whose large latent heats are traditionally accessed using applied magnetic fields. Here, moderate changes of hydrostatic pressure are used to drive giant and reversible inverse barocaloric effects near room temperature in the notoriously brittle magnetocaloric material MnCoGeB . The barocaloric effects compare favorably with those observed in barocaloric materials that are magnetic.

Giant barocaloric effects over a wide temperature range in superionic conductor AgI.

Current interest in barocaloric effects has been stimulated by the discovery that these pressure-driven thermal changes can be giant near ferroic phase transitions in materials that display magnetic or electrical order. Here we demonstrate giant inverse barocaloric effects in the solid electrolyte AgI, near its superionic phase transition at ~420 K. Over a wide range of temperatures, hydrostatic pressure changes of 2.

Perpendicular local magnetization under voltage control in Ni films on ferroelectric BaTiO₃ substrates.

High-resolution magnetoelectric imaging is used to demonstrate electrical control of the perpendicular local magnetization associated with 125 nm-wide magnetic stripe domains in 100-nm-thick Ni films. This magnetoelectric coupling is achieved in zero magnetic field using strain from ferroelectric BaTiO3 substrates to control perpendicular anisotropy imposed by the growth stress. These findings may be exploited for perpendicular recording in nanopatterned hybrid media.

The electrocaloric efficiency of ceramic and polymer films.

Efficiency is defined as η = |Q|/|W| in order to investigate the electrical work |W| associated with electrocaloric heat |Q|. This materials parameter indicates that polymer films are slightly more energy efficient than ceramic films, and therefore both species of material remain candidates for future cooling applications.

A ferroelectric memristor.

Memristors are continuously tunable resistors that emulate biological synapses. Conceptualized in the 1970s, they traditionally operate by voltage-induced displacements of matter, although the details of the mechanism remain under debate. Purely electronic memristors based on well-established physical phenomena with albeit modest resistance changes have also emerged.

Spatially resolved photodetection in leaky ferroelectric BiFeO(3).

Potential gradients due to the spontaneous polarization of BiFeO(3) yield asymmetric and nonlinear photocarrier dynamics. Photocurrent direction is determined by local ferroelectric domain orientation, whereas magnitude is spectrally centered around charged domain walls that are associated with oxygen vacancy migration. Photodetection can be electrically controlled by manipulating ferroelectric domain configurations.

Atomic and electronic structure of the BaTiO3/Fe interface in multiferroic tunnel junctions.

Artificial multiferroic tunnel junctions combining a ferroelectric tunnel barrier of BaTiO(3) with magnetic electrodes display a tunnel magnetoresistance whose intensity can be controlled by the ferroelectric polarization of the barrier. This effect, called tunnel electromagnetoresistance (TEMR), and the corollary magnetoelectric coupling mechanisms at the BaTiO(3)/Fe interface were recently reported through macroscopic techniques. Here, we use advanced spectromicroscopy techniques by means of aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to probe locally the nanoscale structural and electronic modifications at the ferroelectric/ferromagnetic interface.

Solid-state memories based on ferroelectric tunnel junctions.

Ferroic-order parameters are useful as state variables in non-volatile information storage media because they show a hysteretic dependence on their electric or magnetic field. Coupling ferroics with quantum-mechanical tunnelling allows a simple and fast readout of the stored information through the influence of ferroic orders on the tunnel current. For example, data in magnetic random-access memories are stored in the relative alignment of two ferromagnetic electrodes separated by a non-magnetic tunnel barrier, and data readout is accomplished by a tunnel current measurement.

Large electric field effect in electrolyte-gated manganites.

We have studied electrostatic field-induced doping in La0.8Ca0.2MnO3 transistors using electrolyte as a gate dielectric.

Transformation of spin information into large electrical signals using carbon nanotubes.

Spin electronics (spintronics) exploits the magnetic nature of electrons, and this principle is commercially applied in, for example, the spin valves of disk-drive read heads. There is currently widespread interest in developing new types of spintronic devices based on industrially relevant semiconductors, in which a spin-polarized current flows through a lateral channel between a spin-polarized source and drain. However, the transformation of spin information into large electrical signals is limited by spin relaxation, so that the magnetoresistive signals are below 1% (ref.

Charge-ordered ferromagnetic phase in La(0.5)Ca(0.5)MnO3.

Mixed-valent manganites are noted for their unusual magnetic, electronic and structural phase transitions. For example, the La(1-x)Ca(x)MnO(3) phase diagram shows that below transition temperatures in the range 100-260 K, compounds with 0.2 < x < 0.