Probing Giant Magnetism on Fe-N Thin Film by Polarized Neutron Reflectivity

With the development in hard drive and permanent magnet industry, higher saturation magnetization (Ms) or magnetic induction (Bs) material is on high demand. According to the Slater-Pauling curve, the highest Bs value is ~2.45 T, which belongs to FeCo alloy. However, in 1972, Kim and Takahashi [1] announced that the new material Fe-N thin film exhibited an increase in the Bs value of 18%. From then on, tons of research works [2, 3, 4] had been dedicated in this area with conclusions on both sides, achieving either high Bs or low Bs. Among those works, the Bs values were obtained from the measurement of the thin film magnetic moment and its volume, which might cause a considerable amount of error depending on the accuracy of the film thickness and area measurement. Other concerns also include the uncertainty of Ms value due to the subtraction of Fe underlayer. Indeed, a direct measurement of Bs is the key to clarify the discrepancies between these results. Here, we are presenting the method of polarized neutron reflectometry (PNR) to measure the Bs of the partially ordered Fe16N2 thin film. PNR allows the interface magnetism study, [5] the absolute magnetization determination and magnetic depth profile in single thin films, [6, 7, 8, 9] and complicated superlattice structures. [10, 11] In the following scenarios, different partially ordered Fe16N2 thin films are fabricated and are measured using PNR subsequently. Their Bs values are obtained using the fitting results of nuclear scattering length density (NSLD) and magnetic scattering length density (MSLD). Also, a PNR application on FeN thin film will also help us to understand the switching picture of the FeN thin film with external applied field

Highly Tunable Intrinsic Exchange Bias from Interfacial Reconstruction in Epitaxial NixCoyFe3-x-yO4(111)/{\alpha}-Al2O3(0001) Thin Films

Intrinsic exchange bias up to 12.6 kOe is observed in NixCoyFe3-x-yO4(111)/{\alpha}-Al2O3(0001) (0<=x+y<=3) epitaxial thin films where 0.15<=y<=2. An interfacial layer of rock-salt structure emerges between NixCoyFe3-x-yO4 thin films and {\alpha}-Al2O3 substrates and is proposed as the antiferromagnetic layer unidirectionally coupled with ferrimagnetic NixCoyFe3-x-yO4. In NiCo2O4(111)/{\alpha}-Al2O3(0001) films, results of reflection high energy electron diffraction, X-ray photoelectron spectroscopy, X-ray reflectometry, and polarized neutron reflectometry support that the interfacial layer is antiferromagnetic NixCo1-xO (0.32<=x<=0.49) of rock-salt structure; the interfacial layer and exchange bias can be controlled by growth oxygen pressure revealing the key role of oxygen in the mechanism of the interfacial reconstruction. This work establishes a family of intrinsic exchange bias materials with great tunability by stoichiometry and growth parameters and emphasizes the strategy of interface engineering in controlling material functionalities.Comment: Main Text: 14 pages, 5 figures; Supplemental Materials: 12 pages, 11 figure

User s Guide for REFoffSpec Version 1.5.4

This document is a user s guide for the IDL software REFoffSpec version 1.5.4 whose purpose is to aggregate for analysis NeXus data files from the magnetism and liquids reflectometer experiments at the Oak Ridge National Laboratory Spallation Neutron Source. The software is used to scale and align multiple data files that constitute a continuous set for an experimental run. The User s Guide for REFoffSepc explains step by step the process using a specific example run. Output screens are provided to orient the user at each step. The guide documents in detail changes made to the original REFoffSpec code during the period November 2009 and January 2011. At the time of the completion of this version of the code it was accessible from the sns_tools interface as a beta version

Magnetic proximity-induced energy gap of topological surface states

Topological crystalline insulator surface states can acquire an energy gap when time reversal symmetry is broken by interfacing with a magnetic insulator. Such hybrid topological-magnetic insulator structures can be used to generate novel anomalous Hall effects and to control the magnetic state of the insulator in a spintronic device. In this work, the energy gap of topological surface states in proximity with a magnetic insulator is measured using Landau level spectroscopy. The measurements are carried out on Pb1-xSnxSe/EuSe heterostructures grown by molecular beam epitaxy exhibiting record mobility and a low Fermi energy enabling this measurement. We find an energy gap that does not exceed 20meV and we show that is due to the combined effect of quantum confinement and magnetic proximity. The presence of magnetism at the interface is confirmed by magnetometry and neutron reflectivity. The recovered energy gap sets an upper limit for the Fermi level needed to observe the quantized anomalous Hall effect using magnetic proximity heterostructures

Discovery of a high-temperature antiferromagnetic state and transport signatures of exchange interactions in a Bi2Se3/EuSe heterostructure

Spatial confinement of electronic topological surface states (TSS) in topological insulators poses a formidable challenge because TSS are protected by time-reversal symmetry. In previous works formation of a gap in the electronic spectrum of TSS has been successfully demonstrated in topological insulator/magnetic material heterostructures, where ferromagnetic exchange interactions locally lifts the time-reversal symmetry. Here we report an experimental evidence of exchange interaction between a topological insulator Bi2Se3 and a magnetic insulator EuSe. Spin-polarized neutron reflectometry reveals a reduction of the in-plane magnetic susceptibility within a 2 nm interfacial layer of EuSe, and the combination of SQUID magnetometry and Hall measurements points to the formation of an antiferromagnetic layer with at least five-fold enhancement of N\'eel's temperature. Abrupt resistance changes in high magnetic fields indicate interfacial exchange coupling that affects transport in a TSS. High temperature local control of TSS with zero net magnetization unlocks new opportunities for the design of electronic, spintronic and quantum computation devices, ranging from quantization of Hall conductance in zero fields to spatial localization of non-Abelian excitations in superconducting topological qubits

From X-Ray Telescopes to Neutron Focusing

No abstract availabl

Molecular Momentum Transport at Fluid-Solid Interfaces in MEMS/NEMS: A Review

This review is focused on molecular momentum transport at fluid-solid interfaces mainly related to microfluidics and nanofluidics in micro-/nano-electro-mechanical systems (MEMS/NEMS). This broad subject covers molecular dynamics behaviors, boundary conditions, molecular momentum accommodations, theoretical and phenomenological models in terms of gas-solid and liquid-solid interfaces affected by various physical factors, such as fluid and solid species, surface roughness, surface patterns, wettability, temperature, pressure, fluid viscosity and polarity. This review offers an overview of the major achievements, including experiments, theories and molecular dynamics simulations, in the field with particular emphasis on the effects on microfluidics and nanofluidics in nanoscience and nanotechnology. In Section 1 we present a brief introduction on the backgrounds, history and concepts. Sections 2 and 3 are focused on molecular momentum transport at gas-solid and liquid-solid interfaces, respectively. Summary and conclusions are finally presented in Section 4

User s Guide for REFoffSpec Version 1.5.4

This document is a user s guide for the IDL software REFoffSpec version 1.5.4 whose purpose is to aggregate for analysis NeXus data files from the magnetism and liquids reflectometer experiments at the Oak Ridge National Laboratory Spallation Neutron Source. The software is used to scale and align multiple data files that constitute a continuous set for an experimental run. The User s Guide for REFoffSepc explains step by step the process using a specific example run. Output screens are provided to orient the user at each step. The guide documents in detail changes made to the original REFoffSpec code during the period November 2009 and January 2011. At the time of the completion of this version of the code it was accessible from the sns_tools interface as a beta version

Optically Induced Static Magnetization in Metal Halide Perovskite for Spin‐Related Optoelectronics

Abstract Understanding the feasibility to couple semiconducting and magnetic properties in metal halide perovskites through interface design opens new opportunities for creating the next generation spin‐related optoelectronics. In this work, a fundamentally new phenomenon of optically induced magnetization achieved by coupling photoexcited orbital magnetic dipoles with magnetic spins at perovskite/ferromagnetic interface is discovered. The depth‐sensitive polarized neutron reflectometry combined with in situ photoexcitation setup, constitutes key evidence of this novel effect. It is demonstrated that a circularly polarized photoexcitation induces a stable magnetization signal within the depth up to 7.5 nm into the surface of high‐quality perovskite (MAPbBr3) film underneath a ferromagnetic cobalt layer at room temperature. In contrast, a linearly polarized light does not induce any detectable magnetization in the MAPbBr3. The observation reveals that photoexcited orbital magnetic dipoles at the surface of perovskite are coupled with the spins of the ferromagnetic atoms at the interface, leading to an optically induced magnetization within the perovskite’s surface. The finding demonstrates that perovskite semiconductor can be bridged with magnetism through optically controllable method at room temperature in this heterojunction design. This provides the new concept of utilizing spin and orbital degrees of freedom in new‐generation spin‐related optoelectronic devices