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<jats:p>The antiferromagnetic (AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic (FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance (FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, FeCoB/Ru/FeCoB sandwich trilayers with Ru thickness (<jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub>) ranging from 1 Å to 16 Å are prepared by a compositional gradient sputtering (CGS) method. It is revealed that a stress-induced anisotropy is present in the FeCoB films due to the B composition gradient in the samples. A <jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub>-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of 2 Å ≤ <jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub> ≤ 8 Å and over 16 Å, while an FM coupling is present in a range of <jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub> &lt; 2 Å and 9 Å ≤ <jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub> ≤ 14.5 Å. It is interesting that an ultrahigh optical mode (OM) FMR frequency in excess of 20 GHz is obtained in the sample with <jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub> = 2.5 Å under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of <jats:italic>t</jats:italic> <jats:sub>Ru</jats:sub> are verified by Layadi’s rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.</jats:p>

<jats:p>The crystal structure, martensitic transformation and magnetocaloric effect have been studied in all-<jats:italic>d</jats:italic>-metal Ni<jats:sub>35</jats:sub>Co<jats:sub>15</jats:sub>Mn<jats:sub>33</jats:sub>Fe<jats:sub>2</jats:sub>Ti<jats:sub>15</jats:sub> alloy ribbons with different wheel speeds (15 m/s (S15), 30 m/s (S30), and 45 m/s (S45)). All three ribbons crystalize in B2-ordered structure at room temperature with crystal constants of 5.893(2) Å, 5.898(4) Å, and 5.898(6) Å, respectively. With the increase of wheel speed, the martensitic transformation temperature decreases from 230 K to 210 K, the Curie temperature increases slightly from 371 K to 378 K. At the same time, magnetic entropy change (Δ<jats:italic>S</jats:italic> <jats:sub>m</jats:sub>) is also enhanced, as well as refrigeration capacity (<jats:italic>RC</jats:italic>). The maximum Δ<jats:italic>S</jats:italic> <jats:sub>m</jats:sub> of 15.6(39.7) J/kg⋅K and <jats:italic>RC</jats:italic> of 85.5 (212.7) J/kg under Δ<jats:italic>H</jats:italic> = 20 (50) kOe (1 Oe = 79.5775 A⋅m<jats:sup>−1</jats:sup>) appear in S45. The results indicate that the ribbons could be the candidate for solid-state magnetic refrigeration materials.</jats:p>

<jats:p>It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces, characterized by a nonintegrable phase factor that an elementary particle of charge <jats:italic>q</jats:italic> acquires from <jats:italic>A</jats:italic> to <jats:italic>B</jats:italic> points: <jats:inline-formula> <jats:tex-math> <?CDATA $P\exp \left({\rm{i}}\displaystyle \frac{q}{\hslash c}\displaystyle {\int }_{A}^{B}{A}_{\mu }{\rm{d}}{x}^{\mu }\right),$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>P</mml:mi> <mml:mi>exp</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> <mml:mstyle displaystyle="true"> <mml:mfrac> <mml:mi>q</mml:mi> <mml:mrow> <mml:mi>ℏ</mml:mi> <mml:mi>c</mml:mi> </mml:mrow> </mml:mfrac> </mml:mstyle> <mml:mstyle displaystyle="true"> <mml:mrow> <mml:msubsup> <mml:mo>∫</mml:mo> <mml:mi>A</mml:mi> <mml:mi>B</mml:mi> </mml:msubsup> <mml:mrow> <mml:msub> <mml:mi>A</mml:mi> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:mrow> </mml:mstyle> <mml:mi mathvariant="normal">d</mml:mi> <mml:msup> <mml:mi>x</mml:mi> <mml:mi>μ</mml:mi> </mml:msup> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>,</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_8_087104_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> where <jats:italic>A<jats:sub>μ</jats:sub> </jats:italic> is the gauge potential and <jats:italic>P</jats:italic> stands for path ordering. In a many-body system of strongly correlated electrons, if the so-called Mott gap is opened up by interaction, the corresponding Hilbert space will be fundamentally changed. A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics. Protected by the Mott gap, which is clearly identified in the high-<jats:italic>T</jats:italic> <jats:sub>c</jats:sub> cuprate with a magnitude &gt; 1.5 eV, such a singular phase factor can enforce a fractionalization of the electrons, leading to a dual world of exotic elementary particles with a topological gauge structure. A non-Fermi-liquid “parent” state will emerge, in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions, while the main dynamics are dominated by two types of gapped spinons. Antiferromagnetism, superconductivity, and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state. Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness, which lies in the core of a high-<jats:italic>T</jats:italic> <jats:sub>c</jats:sub> superconducting mechanism.</jats:p>

<jats:p>Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin–orbit coupling, which can support a series of broken symmetry states. Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale, and hence, lead to rich quantum states, highlighting promising directions for spintronics and valleytronics. In this article, we mainly review the recent scanning tunneling microscopy (STM) advances on the spin and/or valley polarized states induced by an individual atomic-scale defect in graphene, including a single-carbon vacancy, a nitrogen-atom dopant, and a hydrogen-atom chemisorption. Lastly, we give a perspective in this field.</jats:p>

<jats:p>The effective-medium theory (EMT) has proved successful in modeling the non-saturating linear magnetoresistance induced by inhomogeneity. However, calculating magnetoresistance using the EMT usually involves solving coupled integral equations which have no analytical solutions, and therefore, it is still difficult to directly compare the predictions of EMT with experimental data. Here we demonstrate that the linear magnetoresistance predicted by the EMT can be either exactly formulated or well approximated by a simple analytical equation <jats:inline-formula> <jats:tex-math> <?CDATA $\Delta \rho /{\rho }_{0}=\sqrt{{k}^{2}{B}^{2}+{a}^{2}}-a$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>Δ</mml:mo> <mml:mi>ρ</mml:mi> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mn>0</mml:mn> </mml:msub> <mml:mo>=</mml:mo> <mml:msqrt> <mml:mrow> <mml:msup> <mml:mi>k</mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:msup> <mml:mi>B</mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>+</mml:mo> <mml:msup> <mml:mi>a</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:msqrt> <mml:mo>−</mml:mo> <mml:mi>a</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_31_8_087303_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in a number of known situations. The relations between the EMT parameters and the phenomenological parameters <jats:italic>k</jats:italic> and <jats:italic>a</jats:italic> are evaluated. Our results provide a convenient and effective method for extracting the EMT parameters from experimental data.</jats:p>

<jats:p>Exchange coupling across the interface between a ferromagnetic (FM) layer and an antiferromagnetic (AFM) or another FM layer may induce a unidirectional magnetic anisotropy and/or a uniaxial magnetic anisotropy, which has been extensively studied due to the important application in magnetic materials and devices. In this work, we observed a fourfold magnetic anisotropy in amorphous CoFeB layer when exchange coupling to an adjacent FeRh layer which is epitaxially grown on an SrTiO<jats:sub>3</jats:sub>(001) substrate. As the temperature rises from 300 K to 400 K, FeRh film undergoes a phase transition from AFM to FM phase, the induced fourfold magnetic anisotropy in the CoFeB layer switches the orientation from the FeRh〈 110〉 to FeRh〈 100 〉 directions and the strength is obviously reduced. In addition, the effective magnetic damping as well as the two-magnon scattering of the CoFeB/FeRh bilayer also remarkably increase with the occurrence of magnetic phase transition of FeRh. No exchange bias is observed in the bilayer even when FeRh is in the nominal AFM state, which is probably because the residual FM FeRh moments located at the interface can well separate the exchange coupling between the below pinned FeRh moments and the CoFeB moments.</jats:p>

<jats:p>Low-temperature thermal conductivity (<jats:italic>κ</jats:italic>), as well as the magnetic properties and specific heat, are studied for the frustrated zigzag spin-chain material SrEr<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> by using single-crystal samples. The specific heat data indicate the long-range antiferromagnetic transition at ∼ 0.73 K and the existence of strong magnetic fluctuations. The magnetizations at very low temperatures for magnetic field along the <jats:italic>c</jats:italic> axis (spin chain direction) or the <jats:italic>a</jats:italic> axis reveal the field-induced magnetic transitions. The <jats:italic>κ</jats:italic> shows a strong dependence on magnetic field, applied along the <jats:italic>c</jats:italic> axis or the <jats:italic>a</jats:italic> axis, which is closely related to the magnetic transitions. Furthermore, high magnetic field induces a strong increase of <jats:italic>κ</jats:italic>. These results indicate that thermal conductivity along either the <jats:italic>c</jats:italic> axis or the <jats:italic>a</jats:italic> axis are mainly contributed by phonons, while magnetic excitations play a role of scattering phonons.</jats:p>

<jats:p>As the family of magnetic materials is rapidly growing, two-dimensional (2D) van der Waals (vdW) magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their potential applications. This paper reviews the recent progress on emergent vdW magnetic compounds and their potential applications in devices. First, we summarize the current vdW magnetic materials and their synthetic methods. Then, we focus on their structure and the modulation of magnetic properties by analyzing the representative vdW magnetic materials with different magnetic structures. In addition, we pay attention to the heterostructures of vdW magnetic materials, which are expected to produce revolutionary applications of magnetism-related devices. To motivate the researchers in this area, we finally provide the challenges and outlook on 2D vdW magnetism.</jats:p>

<jats:p>Magnetic skyrmions are two-dimensional localized topological spin-structures characterized by the skyrmion number that measures the number of times of spins wrapping the Bloch sphere. Skyrmions behave like particles under an external stimulus and are promising information carriers. Skyrmions can exist as an isolated object as well as skyrmion condensates in crystal structures, helical/conical states, mazes or irregular stripy states with emergent electromagnetic fields. Thus, skyrmions provide a nice platform for studying fundamental physics, other than its applications in spintronics. In this perspective, we briefly review some recent progress in the field and present an outlook of the fundamental challenges in device applications.</jats:p>

<jats:p>In order to fabricate high-performance inverted perovskite solar cells (PeSCs), an appropriate hole transport layer (HTL) is essential since it will affect the hole extraction at perovskite/HTL interface and determine the crystallization quality of the subsequent perovskite films. Herein, a facile and simple method is developed by adding ethanolamine (ETA) into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as HTL. The doping of a low-concentration ETA can efficiently modify the electrical properties of the PEDOT:PSS film and lower the highest occupied molecular orbital (HOMO) level, which is more suitable for the hole extraction from the perovskite to HTL. Besides, ETA-doped PEDOT:PSS will create a perovskite film with larger grain size and higher crystallinity. Hence, the results show that the open-circuit voltage of the device increases from 0.99 V to 1.06 V, and the corresponding power conversion efficiency (PCE) increases from 14.68% to 19.16%. The alkaline nature of ethanolamine greatly neutralizes the acidity of PEDOT:PSS, and plays a role in protecting the anode, leading the stability of the devices to be improved significantly. After being stored for 2000 h, the PCE of ETA-doped PEDOT:PSS devices can maintain 84.2% of the initial value, which is much higher than 67.1% of undoped devices.</jats:p>