Reversible Disorder in a Room Temperature Ferromagnet

Random magnetic fields, varying from site to site in a magnetic material, are a form of disorder that can determine the local architecture and stability of the magnetic state. In a ferromagnet, the application of an external magnetic field can amplify the effects of the internal random fields and, in principle, harden a magnetic domain, without changing temperature and only for as long as the external field is present. Here, the rare‐earth compound Nd₂Fe₁₄B, formed with a granular morphology of random‐packed, elongated grains, is an experimental realization of the Random Field Ising Model in a room temperature ferromagnet. The application of magnetic fields transverse to the easy axis tunes the coupling between the structural disorder and the magnetic pinning properties. This material both illuminates the intricacies of tunable disorder and serves as a guidepost along the way to developing increased‐density magnetic storage media.     

室温铁磁性Al2O3∶Mn的制备及性质

以Al2O3为衬底利用多能态离子注入法在离子注入设备上制备了一系列具有室温铁磁性的Al2O3:Mn样品.在Al2O3的X射线衍射峰附近发现新的衍射峰,该衍射峰既可能对应一种未知新相,也可能对应Al2O3:Mn固溶体.所有样品都具有磁滞现象和室温铁磁性.     

铁矿石加工方法对其磁性铁含量测定结果的影响

介绍了部分铁矿石的不同加工方法对其磁性铁含量分析结果的影响，对测定磁性铁含量的铁矿石加工方法提出建议。     

New Class of High-TC Diluted Ferromagnetic Semiconductors Based on CaO without Transition Metal Elements

We propose new-type ferromagnetic semiconductors based on CaO and K₂S without any transition metal elements. These materials show transparent and half-metallic ferromagnetism if the deep-impurity-band width (W) induced by doping of C, N, Si, or Ge impurities, and the electron-correlation energy (U) satisfy the Stoners condition of highly correlated electron system (U>W). Based on our first-principles calculations, we demonstrate that these materials satisfy the Stoners condition, and could be new candidates for transparent and half-metallic DMSs.     

Oxygen vacancy-induced short-range ordering as a sole mechanism for enhanced magnetism of spinel ZnFe2O4 prepared via a one-step treatment

Despite being difficult to identify, extremely dilute oxygen vacancies have been widely reported to play an important role in enhancing magnetism in ZnFe₂O₄. The mechanisms underlying this enhanced magnetism have not been well understood for a long time and remain controversial because the formation of oxygen vacancy-rich ZnFe₂O₄ can be accompanied by changes in the chemical/physical characteristics, especially the composition, particle size, surface morphology and cation distribution, which can significantly affect the magnetization. An open and important question is whether and to what extent the enhanced magnetization can be attributed only to oxygen vacancies. In this study, the relationship between the magnetization and oxygen vacancies in ZnFe₂O₄ was definitively determined by using a carefully designed “shake-and-heat” treatment to prepare vacancy-rich samples while keeping the other crystal/surface parameters constant. Compared to the nearly vacancy-free paramagnetism samples, the vacancy-rich samples exhibited a higher magnetization of approximately 5 emu/g at both 300 K and 2 K. The Fe³⁺-O^2--Fe³⁺ superexchange paths broken by oxygen vacancies then resulting in the Fe³⁺-Fe³⁺ ferromagnetism configuration. Meanwhile, the oxygen vacancy is highly diluted then the ferromagnetism configuration is confined in a single super-cell, favoring a short-range magnetic ordering at room temperature. The concentration of oxygen vacancies was calculated to be 0.68% by magnetization measurement. Our results may shed a light on how oxygen vacancies affect magnetism.     

Au and Co3O4 anchored Bi2WO6 with enhanced electron paramagnetic resonance,surface plasmon resonance,nonlinear and magnetic properties

The combination of surface plasmon resonance (SPR) effect with hetero-p–n structure shows promising benefits to optical linear and nonlinear properties. In this study, Au nanoparticles (NPs) decorated p–n hetero-structured Co₃O₄/Bi₂WO₆ composite was synthesized and characterized in terms of the optical linear and nonlinear and magnetic properties, morphology, electron transition, charge transfer, energy band gap, polarizability, SPR effect, and oxygen vacancies using scanning electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Z-scan, ultraviolet–visible spectra, and vibrating sample magnetometer. The combination of Co₃O₄ provided active 3d electrons transition and charge transfer which increased carriers’ concentration and reduced the energy band gap. Au SPR enhanced the internal polarization and strengthened the built-in electric field, yielding strong nonlinear behavior. In addition, magnetic Co₃O₄ endowed sample with room-temperature ferromagnetism which was obviously strengthened by Au NPs. The obtained sample is promising for laser and photonics applications.     

Robust Above‐Room‐Temperature Ferromagnetism in Few‐Layer Antimonene Triggered by Nonmagnetic Adatoms

2D ferromagnets have attracted considerable attention due to their strong potential in the post‐Moore Law era. However, intrinsic 2D ferromagnetic materials typically suffer from suppressed Curie temperature due to thermal fluctuation, magnetic order instability in the 2D limit, and others. Herein, a nonmagnetic fluorine modification strategy is proposed to control the ferromagnetism of air‐stable antimonene. It is demonstrated that fluorinated antimonene (F‐antimonene), synthesized via an electrochemical exfoliation and synchronous fluorination method, exhibits robust ferromagnetism with a Curie temperature of up to 717 K (compared with a Curie temperature of 220 K for pristine antimonene) and a saturation magnetization of ≈0.1 emu g^?1 (determined by the fluorination degree). First‐principles simulations confirm that the robust long‐range ferromagnetic order in the half‐metallic F‐antimonene is induced by the low‐density sp‐electron‐polarized impurity subbands. The study constitutes a nonmagnetic control of robust above‐room‐temperature ferromagnetism in monoelemental 2D semiconductors and paves a new route toward 2D atomic layer‐based spin devices.     

High‐TC Interfacial Ferromagnetism in SrMnO3/LaMnO3 Superlattices

Heterostructures of strongly correlated oxides demonstrate various intriguing and potentially useful interfacial phenomena. LaMnO₃/SrMnO₃ superlattices are presented showcasing a new high‐temperature ferromagnetic phase with Curie temperature, T_C ≈360 K, caused by electron transfer from the surface of the LaMnO₃ donor layer into the neighboring SrMnO₃ acceptor layer. As a result, the SrMnO₃ (top)/LaMnO₃ (bottom) interface shows an enhancement of the magnetization as depth‐profiled by polarized neutron reflectometry. The length scale of charge transfer, λ_TF ≈2 unit cells, is obtained from in situ growth monitoring by optical ellipsometry, supported by optical simulations, and further confirmed by high resolution electron microscopy and spectroscopy. A model of the inhomogeneous distribution of electron density in LaMnO₃/SrMnO₃ layers along the growth direction is concluded to account for a complex interplay between ferromagnetic and antiferromagnetic layers in superlattices.