This article collection appears on the basis of selected presentations made at the International Workshop on Advanced Magnetic Oxides (IWAMO) held online from 24–26 November 2021, based at the University of Aveiro, Portugal. IWAMO-2021 was organized in the framework of the European Project H2020–MSCA–RISE–2017–778308–SPINMULTIFILM – “Physical principles of the creation of novel SPINtronic materials on the base of MULTIlayered metal-oxide FILMs for magnetic sensors and MRAM”.

The time after the first edition of IWAMO in 2019 was overshadowed by the Corona pandemic which made international cooperation unusually difficult. It was all the more important to sustain and develop scientific communication, even if for the most part in the online format.

The workshop continued the exchange of ideas and expertise in the area of magnetic double perovskites, especially, strontium ferromolybdate (SFMO) started at IWAMO-2019, but the scope of the workshop was again much wider than this topic. Magnetism is a fantastic field of research where new results are obtained every day, and we have learned a lot of new information from the keynote and contributed presentations included in the program of our workshop.

The workshop program comprised a total of 14 keynote talks, 16 oral, and 6 poster presentations. The presenting authors came from 18 countries.

The following six papers based on workshop presentations have been selected for publication in a dedicated section of physica status solidi (b):

The article by G. Suchaneck et al.^[1] reviews the resistivity behavior of granular SFMO ceramics comprising intergrain tunnel barriers. The low-field magnetoresistance properties in double-perovskite SFMO core-shell structures arise from spin-dependent tunneling through a barrier formed by the shell. It is strongly dependent on synthesis conditions. Based on this generalization, the modification of the tunneling process with barrier thickness and interface conditions is demonstrated. For the first time, equations for the magnetoresistance in each special case are derived.

N. Kalanda et al.^[2] elucidate the role of the degree of superstructural ordering on the magnetic, magnetocaloric, and electric transport properties of SFMO double perovskites. The saturation magnetization and the Curie temperature of the samples correlate with the degree of superstructural ordering. The Banerjee criterion indicates that the compounds studied undergo a second-order phase transition. Additional low-temperature annealing changes the sample conductivity of metallic type for semiconducting one and significantly increases magnetoresistance due to the intergrain electron tunneling.

R. Lanovsky et al.^[3] studied the properties of Sr_1–xY_xCoO_3–δ layered cobaltites by synchrotron X-ray and neutron powder diffraction and measurements of magnetic and magnetotransport properties. They have shown that crystal structure changes from tetragonal P4/mmm (a_p × a_p × 2a_p) to monoclinic A2/m (4 √ 2a_p × 2 √ 2a_p × 4a_p up to the magnetic ordering temperature and 2 √ 2a_p × 2 √ 2a_p × 4a_p above) through the intermediate tetragonal I4/mmm (2a_p × 2a_p × 4a_p) with alternating layers of CoO₆ and CoO_4+δ. The basic magnetic structure is G-type antiferromagnetic with Co³⁺ ions in a high-spin/low-spin state mixture in both structural layers. The Co³⁺ magnetic moments in the CoO₆ and CoO_4+δ layers are 1.5 μ_B/Co and 2 μ_B/Co for x = 0.1 and 1.8 μ_B/Co and 2.7 μ_B/Co for x = 0.2, respectively. The antiferromagnetic–“ferromagnetic” transition in compounds with x > 0.2 is associated with the structural and orbital disorder. Magnetic transitions are accompanied by structural phase transitions. The presence of the ferromagnetic component is associated with the monoclinic distortions and canting of magnetic moments in anion-deficient layers due to orbital ordering. A sharp drop of the magnetization for x > 0.2 is caused by the LS Co³⁺ stabilization and orbital disordering. No spontaneous magnetization was found for compounds with x > 27%.

The following articles were dedicated to low-dimensional magnetic structures.

K. Tsysar et al.^[4] performed a first-principles study of magneto-optical properties of oxidized Co nanowires on vicinal Pt surfaces. The study reveals a change of magnetic coupling in Co nanowires under oxidation, which is sensitive to the step-edge geometry of the vicinal surface. The dielectric tensor and reflectivity have been calculated for oxide structures in order to find their main features in optical characteristics. Besides, the reflectance difference spectra were constructed for pure and oxidized nanowires in order to reveal the effect of the interplay between magnetic state and oxidation on the optical properties of magnetic nanowires, which could be useful for tailoring their magnetic properties in spintronic devices.

J. Fedotova^[5] sintered silica-coated FeCo nanoparticles ((Fe₂₅Co₇₅)_x(SiO₂)_100–x (90 ≥ x ≥ 10 wt.%) NPs). A study of the morphology and phase composition of the respective nanopowders evidences the formation of agglomerations of NPs with a medium individual diameter of ≈20–50 nm containing partially oxidized cores of α-FeCo bcc alloy covered with amorphous SiO₂. Mössbauer spectroscopy reveals that coverage with SiO₂ shells promotes up to fourfold enhancement of resistance of FeCo cores to the undesirable formation of surface Fe(Co) hydroxides. Temperature dependencies of magnetization for uncoated and silica-coated nanopowders indicate that some fraction of NPs being in the single-domain state form superferromagnetic long-range order.

C. Keßler and G. Gerlach^[6] demonstrate magnetic functionalization of poly(N-isopropyl acrylamide) hydrogels crosslinked with Laponite XLS for sensor applications. The work aimed at introducing high densities of magnetic particles with a homogeneous distribution into the gel. Particles were coated with 3-(trimethoxysilyl)propyl methacrylate to bind them into the network structure. The swelling behavior and temperature response of gels containing pure and modified particles were compared to the unmodified clay gel. Ferrogels were further synthesized in a magnetic field to align magnetic nanoparticles in the network permanently. This resulted in permanently embedded rod-like structures spanning the entire length of the gel. The influence of this anisotropic distribution on the mechanical properties of the hydrogel was investigated through compression measurements.

The workshop was an exciting and fruitful event, a forum for reporting and discussing new findings, exchanging new ideas, and inspiring new concepts and designs.

We greatly acknowledge the University of Aveiro, the Physics Department of the University of Aveiro and the Associate Laboratory i3N/FSCOSD – Institute of Nanostructures, Nanomodelling and Nanofabrication (Aveiro unit) for institutional and administrative support which allowed the successful organization of the IWAMO workshop and the gathering of researchers from various countries. Wiley-VCH kindly arranged the workshop publication.

The Guest Editors

本文章集基于 2021 年 11 月 24 日至 26 日在葡萄牙阿威罗大学在线举行的高级磁性氧化物国际研讨会 (IWAMO) 上的精选演讲而出现。IWAMO-2021 是在欧洲项目 H2020–MSCA–RISE–2017–778308–SPINMULTIFILM 的框架内组织的——“基于用于磁传感器和 MRAM 的多层金属氧化物薄膜的新型 SPINtronic 材料创建的物理原理”。

在 2019 年第一版 IWAMO 之后的时间被电晕大流行所掩盖，这使得国际合作异常困难。维持和发展科学交流更为重要，即使大部分是在线形式。

研讨会继续在磁性双钙钛矿领域交流思想和专业知识，特别是在 IWAMO-2019 开始的钼酸锶 (SFMO) 领域，但研讨会的范围再次比这个主题更广泛。磁性是一个了不起的研究领域，每天都会获得新的成果，我们从主题演讲中学到了很多新信息，并在我们的研讨会计划中提供了演示文稿。

研讨会计划共包括 14 场主题演讲、16 场口头报告和 6 场海报展示。报告作者来自 18 个国家。

以下六篇基于研讨会演讲的论文已被选中在physica status solidi (b)的专门部分发表：

G. Suchaneck 等人的文章。^{[ 1 ]}回顾了包含晶间隧道势垒的粒状 SFMO 陶瓷的电阻率行为。双钙钛矿 SFMO 核壳结构中的低场磁阻特性源于通过壳层形成的势垒的自旋相关隧穿。它强烈依赖于合成条件。基于这种概括，证明了具有势垒厚度和界面条件的隧穿过程的修改。首次导出了每种特殊情况下的磁阻方程。

N. Kalanda 等人。^{[ 2 ]}阐明了上层结构有序度对 SFMO 双钙钛矿的磁性、磁热和电输运性质的作用。样品的饱和磁化强度和居里温度与上层结构有序程度相关。Banerjee 准则表明所研究的化合物经历了二级相变。额外的低温退火改变了用于半导体的金属类型的样品电导率，并且由于晶间电子隧道效应而显着增加了磁阻。

R.拉诺夫斯基等人。^{[ 3 ]}通过同步加速器 X 射线和中子粉末衍射以及磁性和磁输运性质的测量，研究了 Sr _{1– x} Y _x CoO _{3– δ层状钴酸盐的性质。}他们表明晶体结构从四方 P4/mmm ( a _p  ×  a _p  × 2 a _p ) 变为单斜晶 A2/m (4 √ 2 a _p  × 2 √ 2 a _p  × 4 a _p直至磁有序温度和 2 √ 2 a _p  × 2 √ 2 a _p × 4 a _p以上）通过中间四方 I4/mmm (2 a _p  × 2 a _p  × 4 a _p ) 与 CoO ₆和 CoO _{4+ δ}交替层。基本磁性结构是G型反铁磁性，在两个结构层中具有高自旋/低自旋态混合物的Co ^3+离子。对于x  = 0.1 和 1.8 μ _B /Co 和 2.7 μ _{B ，CoO 6}和 CoO _{4+ δ}层中的 Co ³⁺磁矩为 1.5 μ _B /Co 和 2 μ _{B /Co}/Co 分别表示x  = 0.2。x > 0.2的化合物中的反铁磁-“铁磁”跃迁 与结构和轨道紊乱有关。磁跃迁伴随着结构相变。由于轨道排序，铁磁成分的存在与阴离子缺陷层中的单斜晶畸变和磁矩倾斜有关。x > 0.2的磁化强度急剧下降 是由LS Co ³⁺稳定化和​​轨道无序引起的。对于x  > 27%的化合物，没有发现自发磁化。

以下文章致力于低维磁性结构。

K. Tsysar 等人。^{[ 4 ]}对邻位 Pt 表面上氧化的 Co 纳米线的磁光特性进行了第一性原理研究。该研究揭示了氧化下钴纳米线中磁耦合的变化，这对邻面的阶梯边缘几何形状很敏感。已经计算了氧化物结构的介电张量和反射率，以便找到它们在光学特性中的主要特征。此外，构建了纯纳米线和氧化纳米线的反射率差异光谱，以揭示磁性纳米线和氧化之间的相互作用对磁性纳米线光学性质的影响，这可能有助于在自旋电子器件中调整其磁性。

J. Fedotova ^{[ 5 ]}烧结二氧化硅包覆的 FeCo 纳米颗粒（(Fe ₂₅ Co ₇₅ ) _x (SiO ₂ ) _{100– x} (90 ≥  x  ≥ 10 wt.%) NPs）。对各个纳米粉末的形态和相组成的研究表明，形成了中等直径约 20-50 nm 的 NPs 团聚体，其中包含覆盖有非晶 SiO _2的α -FeCo bcc合金的部分氧化核。穆斯堡尔光谱揭示了 SiO _2的覆盖壳将 FeCo 核对表面 Fe(Co) 氢氧化物的不希望形成的抵抗力提高了四倍。未涂覆和涂覆二氧化硅的纳米粉末的磁化温度依赖性表明部分处于单畴状态的纳米颗粒形成超铁磁长程有序。

C. Keßler 和 G. Gerlach ^{[ 6 ]}展示了与 Laponite XLS 交联的聚（N-异丙基丙烯酰胺）水凝胶的磁性功能化，用于传感器应用。该工作旨在将具有均匀分布的高密度磁性颗粒引入凝胶中。用甲基丙烯酸3-(三甲氧基甲硅烷基)丙酯涂覆颗粒以将它们结合到网络结构中。将含有纯颗粒和改性颗粒的凝胶的溶胀行为和温度响应与未改性的粘土凝胶进行了比较。在磁场中进一步合成铁凝胶，以使网络中的磁性纳米颗粒永久排列。这导致永久嵌入的棒状结构跨越凝胶的整个长度。通过压缩测量研究了这种各向异性分布对水凝胶机械性能的影响。

研讨会是一个激动人心且富有成果的活动，是一个报告和讨论新发现、交流新想法、启发新概念和设计的论坛。

我们非常感谢阿威罗大学、阿威罗大学物理系和 i3N/FSCOSD 副实验室——纳米结构、纳米建模和纳米制造研究所（阿威罗单位）提供的制度和行政支持，使 IWAMO 研讨会的成功组织和来自不同国家的研究人员的聚会。Wiley-VCH 友好地安排了研讨会出版物。

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