arXiv subjects

Valeria Lauter

Publications and source records attributed to Valeria Lauter.

24 records · Page 2Linked to original sources

arXiv2021

Magnetic charge's relaxation propelled electricity in two-dimensional magnetic honeycomb lattice

Emerging new concepts, such as magnetic charge dynamics in two-dimensional magnetic material, can provide novel mechanism for spin based electrical transport at macroscopic length. In artificial spin ice of single domain elements, magnetic charge's relaxation can create an efficient electrical pathway for conduction by generating fluctuations in local magnetic field that couple with conduction electrons spins. In a first demonstration, we show that the electrical conductivity is propelled by more than an order of magnitude at room temperature due to magnetic charge defects sub-picosecond relaxation in artificial magnetic honeycomb lattice. The direct evidence to the proposed electrical conduction mechanism in two-dimensional frustrated magnet points to the untapped potential for spintronic applications in this system.

cond-mat.mes-hall↗

arXiv2016

Enhancing interfacial magnetization with a ferroelectric

Ferroelectric control of interfacial magnetism has attracted much attention. However, the coupling of these two functionalities has not been understood well at the atomic scale. The lack of scientific progress is mainly due to the limited characterization methods by which the interface's magnetic properties can be probed at an atomic level. Here, we use polarized neutron reflectometry (PNR) to probe the evolution of the magnetic moment at interfaces in ferroelectric/strongly correlated oxide [PbZr0.2Ti0.8O3/La0.8Sr0.2MnO3 (PZT/LSMO)] heterostructures. We find that there is always suppressed magnetization at the surface and interface of LSMO and such magnetic deterioration can be strongly improved by interfacing with a strongly polar PZT film. The magnetoelectric coupling of magnetism and ferroelectric polarization occurs within a couple of nanometers of the interface as demonstrated by the enhanced interfacial magnetization beyond the bulk value by 5% depending on the polarization of PZT. The latter value is 70% higher than the surface magnetization of a LSMO film without interfacing with a ferroelectric layer. These compelling results not only probe the presence of nanoscale magnetic suppression and its control by ferroelectrics, but also emphasize the importance of utilizing probing techniques that can distinguish between bulk and interfacial phenomena.

cond-mat.str-el↗

arXiv2016

Emerging magnetism and anomalous Hall effect in iridate-manganite heterostructures

Strong Coulomb repulsion and spin-orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Initial attempts to investigate systems where both of these fundamental interactions are comparably strong, such as 3d and 5d complex oxide superlattices, have revealed properties that only slightly differ from the bulk ones of the constituent materials. Here, we observe that the interfacial coupling between the 3d antiferromagnetic insulator SrMnO3 and the 5d paramagnetic metal SrIrO3 is enormously strong, yielding an anomalous Hall response as the result of charge transfer driven interfacial ferromagnetism. These findings show that low dimensional spin-orbit entangled 3d-5d interfaces provide an avenue to uncover technologically relevant physical phenomena unattainable in bulk materials.

cond-mat.str-el↗

arXiv2012

Polarized neutron reflectometry study of Fe16N2 with Giant Saturation Magnetization prepared by N Inter-diffusion in Annealed Fe-N Thin Films

We report a synthesis route to grow iron nitride thin films with giant saturation magnetization (Ms) through an N inter-diffusion process. By post annealing Fe/Fe-N structured films grown on GaAs(001) substrates, nitrogen diffuses from the over-doped amorphous-like Fe-N layer into strained crystalline Fe layer and facilitates the development of metastable Fe16N2 phase. As explored by polarized neutron reflectometry, the depth-dependent Ms profile can be well described by a model with the presence of a giant Ms up to 2360 emu/cm3 at near-substrate interface, corresponding to the strained regions of these annealed films. This is much larger than the currently known limit (Fe65Co35 with Ms \sim 1900 emu/cm3). The present synthesis method can be used to develop writer materials for future magnetic recording application.

cond-mat.mtrl-sci↗

arXiv2012

Direct Observation of Giant Saturation Magnetization in Fe16N2

Magnetic materials with giant saturation magnetization have been a holy grail for magnetic researchers and condensed matter physicists for decades because of its great scientific and technological impacts. As described by the famous Slater-Pauling curve the material with highest Ms is the Fe65Co35 alloy. This was challenged in 1972 by a report on the compound Fe16N2 with Ms much higher than that of Fe65Co35. Following this claim, there have been enormous efforts to reproduce this result and to understand the magnetism of this compound. However, the reported Ms by different groups cover a broad range, mainly due to the unavailability of directly assessing Ms in Fe16N2. In this article, we report a direct observation of the giant saturation magnetization up to 2500 emu/cm3 using polarized neutron reflectometry (PNR) in epitaxial constrained Fe16N2 thin films prepared using a low-energy and surface-plasma-free sputtering process. The observed giant Ms is corroborated by a previously proposed Cluster + Atom model, the characteristic feature of which, namely, the directional charge transfer is evidenced by polarization-dependent x-ray absorption near edge spectroscopy (XANES).

cond-mat.mtrl-sci↗

arXiv2012

Giant saturation magnetization effect in epitaxial Fe16N2 thin films grown on MgO (001) substrate

Whether αdouble prime-Fe16N2 possesses a giant saturation magnetization (Ms) has been a daunting problem among magnetic researchers for almost 40 years, mainly due to the unshakable faith of famous Slater-Pauling (SP) curve and poor consistency on evaluating its Ms. Here we demonstrate that, using epitaxy and mis-fit strain imposed by an underlying substrate, the in-plane lattice constant of Fe16N2 thin films can be fine tuned to create favorable conditions for exceptionally large saturation magnetization. Combined study using polarized neutron reflectometry and X-ray diffraction shows that with increasing strain at the interface the Ms of these film can be changed over a broad range, from ~2.1T (non-high Ms) up to ~3.1T (high Ms). We suggest that the equilibrium in-plane lattice constant of Fe16N2 sits in the vicinity of the spin crossover point, in which a transition between low spin to high spin configuration of Fe sites can be realized with sensitive adjustment of crystal structure.

cond-mat.mtrl-sci↗