Chiral effects at the metal center in Fe(III) spin crossover coordination salts.

Evidence of chirality was observed at the Fe metal center in Fe(III) spin crossover coordination salts [Fe(qsal)][Ni(dmit)] and [Fe(qsal)](TCNQ)from x-ray absorption (XAS) spectroscopy at the Fe 2pcore threshold. Based on the circularly polarized XAS data, the x-ray natural circular dichroism for [Fe(qsal)][Ni(dmit)] and [Fe(qsal)](TCNQ)is far stronger than seen for [Fe(qsal)]Cl suggesting this natural circular dichroism signature is a ligand effect rather than a result of just a loss of octahedral symmetry on the Fe core. The larger the chiral effects in the Fe 2p core to bound XAS, the greater the perturbation of the Fe 2pto 2pspin-orbit splitting seen in the XAS spectra.

A fully contained sample holder capable of electron-yield detection at soft X-ray energies.

A holder has been developed that enables electron yield-detected soft X-ray spectroscopy of fully contained samples at low temperature. Crucially, this design uses elements of the sample containment to collect ejected electrons, removing the need to expose samples directly to the vacuum environment of the spectrometer. The design is modular and should be adaptable to a number of different endstation configurations, enabling spectroscopy of air-sensitive, radioactive and vacuum-sensitive (biological) samples.

Hydrogen-Induced Topotactic Phase Transformations of Cobaltite Thin Films.

Manipulating physical properties through ion migration in complex oxide thin films is an emerging research direction to achieve tunable materials for advanced applications. While the reduction of complex oxides has been widely reported, few reports exist on the modulation of physical properties through a direct hydrogenation process. Here, we report an unusual mechanism for hydrogen-induced topotactic phase transitions in perovskite LaSrCoO thin films.

Evidence of Cooperative Effects for the Fe(phen)(NCS) Spin Crossover Molecular Complex in Polyaniline Plus Iron Magnetite.

The spin crossover complex Fe(phen)(NCS) and its composite, Fe(phen)(NCS), combined with the conducting polymer polyaniline (PANI) plus varying concentrations of iron magnetite (FeO) nanoparticles were studied. A cooperative effect is evident from the hysteresis width in the plot of magnetic susceptibility multiplied by temperature versus temperature (χmT versus T) for Fe(phen)(NCS) with PANI plus varying concentrations of FeO nanoparticles. The hysteresis width in the composites vary no more than 2 K with respect to the pristine Fe(phen)(NCS) spin crossover crystallites despite the fact that there exists a high degree of miscibility of the Fe(phen)(NCS) spin crossover complex with the PANI.

Conductance fluctuations in cobalt valence tautomer molecular thin films.

The conductivity changes associated with optical excitations and changing temperature in cobalt valence tautomer molecular thin films were investigated. Conductance switching in the presence of illumination is observed, with occasional locking in a higher conductance state, depending on the temperature, the photon energy of the illumination, and the bias voltage. Light of sufficiently short wavelengths is needed to ensure the light enhanced conductance switching, consistent with the optical absorption, but bias voltage clearly plays a role as well.

Layer-by-layer assembly of a [Fe-(pyrazine){Pd(CN)}] spin crossover thin film.

[Fe-(pyrazine){Pd(CN)}] (pyrazine = pz) thin films were fabricated using a layer-by-layer assembly approach, a method known to be tunable, versatile, and scalable, since thin films are better-suited for industrial applications. In this study, [Fe-(pz){Pd(CN)}] powder was synthesized, and the results obtained from a vibrating sample magnetometer verified the presence of an abrupt hysteresis loop with widths of 45 K centered around 300 K, indicating good cooperativity. Super conducting quantum interference device magnetometry results indicated a slow spin transition with temperature but with evidence of hysteresis for thin film samples.

Imaging of voltage-controlled switching of magnetization in highly magnetostrictive epitaxial Fe-Ga microstructures.

The magnetoelectric behavior of epitaxial Fe-Ga microstructures on top of a (001)-oriented PMN-PT piezoelectric substrate is imaged with magnetic X-ray microscopy. Additionally, the micron-scale strain distribution in PMN-PT is characterized by X-ray microdiffraction and examined with respect to the results of the Fe-Ga magnetoelectric switching. The magnetic reorientation of Fe-Ga is found to be strongly correlated with size, shape, and crystallographic orientation of the microstructures.

Tuning In-Plane Magnetic Anisotropy and Interfacial Exchange Coupling in Epitaxial LaSrCoO/LaSrMnO Heterostructures.

Controlling the in-plane magnetocrystalline anisotropy and interfacial exchange coupling between ferromagnetic (FM) layers plays a key role in next-generation spintronic and magnetic memory devices. In this work, we explored the effect of tuning the magnetocrystalline anisotropy of LaSrCoO (LSCO) and LaSrMnO (LSMO) layers and the corresponding effect on interfacial exchange coupling by adjusting the thickness of the LSCO layer (). The epitaxial LSCO/LSMO bilayers were grown on (110)-oriented NdGaO (NGO) substrates with a fixed LSMO (top layer) thickness of 6 nm and LSCO (bottom layer) thicknesses varying from 1 to 10 nm.

Element-Specific Study of Magnetic Anisotropy and Hardening in SmCoCu Thin Films.

This work investigates the effect of copper substitution on the magnetic properties of SmCo thin films synthesized by molecular beam epitaxy. A series of thin films with varying concentrations of Cu were grown under otherwise identical conditions to disentangle structural and compositional effects on the magnetic behavior. The combined experimental and theoretical studies show that Cu substitution at the Co sites not only stabilizes the formation of the SmCo structure but also enhances magnetic anisotropy and coercivity.

Ultra-thin lithium aluminate spinel ferrite films with perpendicular magnetic anisotropy and low damping.

Ultra-thin films of low damping ferromagnetic insulators with perpendicular magnetic anisotropy have been identified as critical to advancing spin-based electronics by significantly reducing the threshold for current-induced magnetization switching while enabling new types of hybrid structures or devices. Here, we have developed a new class of ultra-thin spinel structure LiAlFeO (LAFO) films on MgGaO (MGO) substrates with: 1) perpendicular magnetic anisotropy; 2) low magnetic damping and 3) the absence of degraded or magnetic dead layers. These films have been integrated with epitaxial Pt spin source layers to demonstrate record low magnetization switching currents and high spin-orbit torque efficiencies.

Systematic Control of Ferrimagnetic Skyrmions via Composition Modulation in Pt/FeTb/Ta Multilayers.

Magnetic skyrmions are topological spin textures that can be used as memory and logic components for advancing the next generation spintronics. In this regard, control of nanoscale skyrmions, including their sizes and densities, is of particular importance for enhancing the storage capacity of skyrmionic devices. Here, we propose a viable route for engineering ferrimagnetic skyrmions via tuning the magnetic properties of the involved ferrimagnets FeTb.

Limits to the strain engineering of layered square-planar nickelate thin films.

The layered square-planar nickelates, NdNiO, are an appealing system to tune the electronic properties of square-planar nickelates via dimensionality; indeed, superconductivity was recently observed in NdNiO thin films. Here, we investigate the role of epitaxial strain in the competing requirements for the synthesis of the n = 3 Ruddlesden-Popper compound, NdNiO, and subsequent reduction to the square-planar phase, NdNiO. We synthesize our highest quality NdNiO films under compressive strain on LaAlO (001), while NdNiO on NdGaO (110) exhibits tensile strain-induced rock salt faults but retains bulk-like transport properties.

Evidence of symmetry breaking in a Gd di-nuclear molecular polymer.

A chiral 3D coordination compound, [Gd(L)(ox)(HO)], arranged around a dinuclear Gd unit has been characterized by X-ray photoemission and X-ray absorption measurements in the context of density functional theory studies. Core level photoemission of the Gd 5p multiplet splittings indicates that spin orbit coupling dominates over j-J coupling evident in the 5p core level spectra of Gd metal. Indications of spin-orbit coupling are consistent with the absence of inversion symmetry due to the ligand field.

Domain-wall magnetoelectric coupling in multiferroic hexagonal YbFeO films.

Electrical modulation of magnetic states in single-phase multiferroic materials, using domain-wall magnetoelectric (ME) coupling, can be enhanced substantially by controlling the population density of the ferroelectric (FE) domain walls during polarization switching. In this work, we investigate the domain-wall ME coupling in multiferroic h-YbFeO thin films, in which the FE domain walls induce clamped antiferromagnetic (AFM) domain walls with reduced magnetization magnitude. Simulation according to the phenomenological theory indicates that the domain-wall ME effect is dramatically enhanced when the separation between the FE domain walls shrinks below the characteristic width of the clamped AFM domain walls during the ferroelectric switching.

Electronic structure of cobalt valence tautomeric molecules in different environments.

Future molecular microelectronics require the electronic conductivity of the device to be tunable without impairing the voltage control of the molecular electronic properties. This work reports the influence of an interface between a semiconducting polyaniline polymer or a polar poly-D-lysine molecular film and one of two valence tautomeric complexes, , [Co(SQ)(Cat)(4-CN-py)] ↔ [Co(SQ)(4-CN-py)] and [Co(SQ)(Cat)(3-tpp)] ↔ [Co(SQ)(3-tpp)]. The electronic transitions and orbitals are identified using X-ray photoemission, X-ray absorption, inverse photoemission, and optical absorption spectroscopy measurements that are guided by density functional theory.

Intermolecular interaction and cooperativity in an Fe(II) spin crossover molecular thin film system.

Compact domain features have been observed in spin crossover [Fe{HB(pz)}(bipy)] molecular thin film systems via soft x-ray absorption spectroscopy and photoemission electron microscopy. The domains are in a mixed spin state that on average corresponds to roughly 2/3 the high spin occupation of the pure high spin state. Monte Carlo simulations support the presence of intermolecular interactions that can be described in terms of an Ising model in which interactions beyond nearest-neighbors cannot be neglected.

Printing Air-Stable High- Molecular Magnet with Tunable Magnetic Interaction.

High- molecular magnets have amassed much promise; however, the long-standing obstacle for its practical applications is the inaccessibility of high-temperature molecular magnets showing dynamic and nonvolatile magnetization control. In addition, its functional durability is prone to degradation in oxygen and heat. Here, we introduce a rapid prototyping and stabilizing strategy for high (360 K) molecular magnets with precise spatial control in geometry.

Evidence of dynamical effects and critical field in a cobalt spin crossover complex.

The [Co(SQ)(4-CN-py)] complex exhibits dynamical effects over a wide range of temperature. The orbital moment, determined by X-ray magnetic circular dichroism (XMCD) with decreasing applied magnetic field, indicates a nonzero critical field for net alignment of magnetic moments, an effect not seen with the spin moment of [Co(SQ)(4-CN-py)].

Evidence for surface effects on the intermolecular interactions in Fe(II) spin crossover coordination polymers.

From X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS), it is evident that the spin state transition behavior of Fe(II) spin crossover coordination polymer crystallites at the surface differs from the bulk. A comparison of four different coordination polymers reveals that the observed surface properties may differ from bulk for a variety of reasons. There are Fe(II) spin crossover coordination polymers with either almost complete switching of the spin state at the surface or no switching at all.

Superconductivity in a quintuple-layer square-planar nickelate.

Since the discovery of high-temperature superconductivity in copper oxide materials, there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconducting materials. One prime materials platform has been the rare-earth nickelates and, indeed, superconductivity was recently discovered in the doped compound NdSrNiO (ref. ).

Transition Metal Synthetic Ferrimagnets: Tunable Media for All-Optical Switching Driven by Nanoscale Spin Current.

All-optical switching of magnetization has great potential for use in future ultrafast and energy efficient nanoscale magnetic storage devices. So far, research has been almost exclusively focused on rare-earth based materials, which limits device tunability and scalability. Here, we show that a perpendicularly magnetized synthetic ferrimagnet composed of two distinct transition metal ferromagnetic layers, NiPt and Co, can exhibit helicity independent magnetization switching.

Proton switching molecular magnetoelectricity.

The convergence of proton conduction and multiferroics is generating a compelling opportunity to achieve strong magnetoelectric coupling and magneto-ionics, offering a versatile platform to realize molecular magnetoelectrics. Here we describe machine learning coupled with additive manufacturing to accelerate the design strategy for hydrogen-bonded multiferroic macromolecules accompanied by strong proton dependence of magnetic properties. The proton switching magnetoelectricity occurs in three-dimensional molecular heterogeneous solids.