Revealing the origin of the vertical hysteresis loop shifts in an exchange biased Co/YMnO3 bilayer

Molecular Tunability of Magnetic Exchange Bias and Asymmetrical Magnetotransport in Metalloporphyrin/Co Hybrid Bilayers

Individual molecular spins are promising quantum states for emerging computation technologies. The "on surface" configuration of molecules in proximity to a magnetic film allows control over the orientations of molecular spins and coupling between them. The stacking of planar molecular spins could favor antiferromagnetic interlayer couplings and lead to pinning of the magnetic underlayer via the exchange bias, which is extensively utilized in ultrafast and high-density spintronics. However, fundamental understanding of the molecular exchange bias and its operating features on a device has not been unveiled. Here, we showed tunable molecular exchange bias and its asymmetrical magnetotransport characteristics on a device by using the metalloporphyrin/cobalt hybrid films. A series of the distinctive molecular layers showcased a wide range of the interfacial exchange coupling and bias. The transport behaviors of the hybrid bilayer films revealed the molecular exchange bias effect on a fabricated device, representing asymmetric characteristics on anisotropic and angle-dependent magnetoresistances. Theoretical simulations demonstrated close correlations among the interfacial distance, magnetic interaction, and exchange bias. This study of the hybrid interfacial coupling and its impact on magnetic and magnetotransport behaviors will extend functionalities of molecular spinterfaces for emerging information technologies.

Air-Stable Anisotropic Monocrystalline Nickel Nanowires Characterized Using Electron Holography

Nickel is capable of discharging electric and magnetic shocks in aerospace materials thanks to its conductivity and magnetism. Nickel nanowires are especially desirable for such an application as electronic percolation can be achieved without significantly increasing the weight of the composite material. In this work, single-crystal nickel nanowires possessing a homogeneous magnetic field are produced via a metal-organic precursor decomposition synthesis in solution. The nickel wires are 20 nm in width and 1-2 μm in length. The high anisotropy is attained through a combination of preferential crystal growth in the ⟨100⟩ direction and surfactant templating using hexadecylamine and stearic acid. The organic template ligands protect the nickel from oxidation, even after months of exposure to ambient conditions. These materials were studied using electron holography to characterize their magnetic properties. These thin nanowires display homogeneous ferromagnetism with a magnetic saturation (517 ± 80 emu cm^-3), which is nearly equivalent to that of bulk nickel (557 emu cm^-3). Nickel nanowires were incorporated into carbon composite test pieces and were shown to dramatically improve the electric discharge properties of the composite material.

Modulating Magnetic Properties by Tailoring In-Plane Domain Structures in Hexagonal YMnO3 Films

Periodic structures and the coupling of multiorder parameters in complex oxides heterojunctions can generate exotic properties, of interest both for fundamental researches and for device applications. Here, we report a self-assembling in-plane periodic domain structure, and the resulting rich magnetic states, in a h-YMnO3 thin film fabricated on c-face sapphire substrate. Detailed structural investigations at atomic-level reveal the fashion of alternating domains under tensile or compressive strains separated by a boundary region. Tuned by this in-plane domain structure, the abnormal magnetic properties, such as the ferromagnetic enhancement and the unexpected spin glass state (below ∼38 K), are realized. Moreover, the existence of ferroelectric polarization is confirmed by scanning transmission electron microscopy, which brings in the chances of magnetoelectric coupling effect. These results manifest the close connections between the magnetic properties and such in-plane microstructures, suggesting the possibility of tuning the coupling effects via strain engineering in the hexagonal manganite film.

Shell-ferromagnetism of nano-Heuslers generated by segregation under magnetic field

We report on a new functional property in an AF martensitic Heusler Ni₅₀Mn₄₅In₅, which when annealed at high temperatures under a magnetic field, segregates and forms Ni₅₀Mn₂₅In₂₅ Heusler precipitates embedded in a Ni₅₀Mn₅₀ matrix. The precipitates are paramagnetic whereas the matrix is antiferromagnetic. However, the spins at the interface with the Ni₅₀Mn₅₀ matrix align with the field during their nucleation and growth and become strongly pinned in the direction of the applied field during annealing, whereas the core spins become paramagnetic. This shell-ferromagnetism persists up to 600 K and is so strongly pinned that the remanent magnetization remains unchanged, even when the field is reversed or when the temperature is cycled between low temperatures and close to the annealing temperature.

Interfacial exchange coupling induced anomalous anisotropic magnetoresistance in epitaxial γ'-Fe₄N/CoN bilayers

Anisotropic magnetoresistance (AMR) of the facing-target reactively sputtered epitaxial γ'-Fe4N/CoN bilayers is investigated. The phase shift and rectangular-like AMR appears at low temperatures, which can be ascribed to the interfacial exchange coupling. The phase shift comes from the exchange bias (EB) that makes the magnetization lag behind a small field. When the γ'-Fe4N thickness increases, the rectangular-like AMR appears. The rectangular-like AMR should be from the combined contributions including the EB-induced unidirectional anisotropy, intrinsic AMR of γ'-Fe4N layer and interfacial spin scattering.

Asymmetric magnetoconductance and magneto-Coulomb effect in a carbon nanotube single electron transistor

We report single step-like asymmetric magnetoconductance from a double-walled carbon nanotube single electron transistor contacted by ferromagnetic cobalt electrodes. The device conductance changed significantly when the direction of the applied magnetic field was reversed, but did not show the spin-valve-type double extrema feature near the coercive field of the electrodes. The magnetoconductance also showed quasi-periodic sign-reversing oscillations with respect to the applied bias. The bias-dependent oscillation of the magnetoconductance was compared with the quantum dot stability diagram for the device. As a result, it was confirmed that the asymmetric magnetoconductance was caused by the magneto-Coulomb effect.