Nature of the magnetism of iridium in the double perovskite Sr2CoIrO6
S. Agrestini, K. Chen, C. -Y. Kuo, L. Zhao, H. -J. Lin, C. -T. Chen, A. Rogalev, P. Ohresser, T. -S. Chan, S. -C. Weng, A. C. Komarek, K. Yamaura, M. W. Haverko… 展开作者
S. Agrestini, K. Chen, C. -Y. Kuo, L. Zhao, H. -J. Lin, C. -T. Chen, A. Rogalev, P. Ohresser, T. -S. Chan, S. -C. Weng, A. C. Komarek, K. Yamaura, M. W. Haverkort, Z. Hu, L. H. Tjeng
We report on our investigation on the magnetism of the iridate double perovskite Sr$_2$CoIrO$_6$, a nominally Ir$^{5+}$ Van Vleck $J_{eff}=0$ system. Using x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy at the Ir-$L_{2,3}$ edges, we found a nearly zero orbital contribution to the magnetic moment and thus an apparent breakdown of the $J_{eff}=0$ ground state. By carrying out also XAS and XMCD experiments at the Co-$L_{2,3}$ edges and by performing detailed full atomic multiplet calculations to simulate all spectra, we discovered that the compound consists of about 90% Ir$^{5+}$ ($J_{eff}=0$) and Co$^{3+}$ ($S=2$) and 10% Ir$^{6+}$ ($S=3/2$) and Co$^{2+}$ ($S=3/2$). The magnetic signal of this minority Ir$^{6+}$ component is almost equally strong as that of the main Ir$^{5+}$ component. We infer that there is a competition between the Ir$^{5+}$-Co$^{3+}$ and the Ir$^{6+}$-Co$^{2+}$ configurations in this stoichiometric compound.
High purity polycrystalline Na0.5La0.5RuO3 was synthesized by a solid state method, and its properties were studied by magnetic susceptibility, heat capacity and resistivity measurements. We find it to be a tetragonal perovskite, in contrast to an earlier report, with random La/Na mixing. With a Curie-Weiss temperature of -231 K and effective moment of 2.74 uB/mol-Ru, there is no magnetic ordering down to 1.8 K. A broad hump at 1.4 K in the heat capacity, however, indicates the presence of a glassy magnetic transition, which we attribute to the influence of the random distribution of Na and La…
Robust Half-Metallic Character and Large Oxygen Magnetism in a Perovskite Cuprate
新型钙钛矿铜酸盐材料Sr $_{8}$ CaRe $_{3}$ Cu $_{4}$ O $_{24}$具有铁磁性质，居里温度高（$T_c \sim$ 440 K），通过密度泛函理论计算发现，在空穴掺杂或化学取代后，表现出几个令人惊讶的性质：（1）通过用W或Mo取代Re实现了半金属（HM），而$T_c$保持较高;（2）空穴掺杂的Sr $_{8}$ CaRe $_{3}$ Cu $_{4}$ O $_{24}$也是具有高$T_c$的HM。此外，我们发现，O原子将携带一个大的磁矩空穴掺杂后，这是在强烈的对比，在固体磁性的普遍接受的概念，需要部分填充的$d$或$f$电子在阳离子的壳。因此，材料Sr $_8$ CaRe $_3$ Cu $_4$ O $_{24}$有望为材料设计和开发提供非常有用的平台。
AMX$_3$ compounds are structurally diverse, a notable example being the post-perovskite structure which adopts a two-dimensional framework with corner- and edge-sharing octahedra. Few molecular post-perovskites are known and of these, none have reported magnetic structures. Here we report the synthesis, structure and magnetic properties of molecular post-perovskites: CsNi(NCS)$_3$, a thiocyanate framework, and two new isostructural analogues CsCo(NCS)$_3$ and CsMn(NCS)$_3$. Magnetisation measurements show that all three compounds undergo magnetic order. CsNi(NCS)$_3$ (Curie temperature, $T_\ma…
We present a comprehensive experimental study of magnetization and magnetocaloric effect (MCE) in double perovskite (DP) materials $R_2$NiMnO$_6$ with $R =$ Pr, Nd, Sm, Gd, Tb, and Dy. While a paramagnetic to ferromagnetic transition, with T$_{\rm C}$ in the range $\sim 100 - 200~$K, is a common feature that can be attributed to the ordering of Mn$^{4+}$ and Ni$^{2+}$ magnetic moments, qualitatively distinct behavior depending on the choice of $R$ is observed at low temperatures. These low-temperature anomalies in magnetization are also manifest in the change in magnetic entropy, $-ΔS_{M}$, wh…
Understanding the controlling principles of band gaps trends in d electron perovskites is needed both for gauging metal-insulator transitions, as well as their application in catalysis and doping. The magnitude of this band gap is rather different for different magnetic spin configurations. We find via electronic structure theory that the factors that connect gapping magnitudes to magnetism depend on the nature of the band edge orbital character (BEOC) and surprisingly scale with the number of antiferromagnetic contacts z$_i$ between neighboring transition metal ions. The dependence is weak wh…
Strongly frustrated 2D magnetism in a 3D hexagonal perovskite
East China Normal University（华东师范大学）；University of Science and Technology of China（中国科学技术大学）；Chinese Academy of Sciences（中国科学院）；Huazhong University of Science and Technology（华中科技大学）；Shanghai Jiao Tong University（上海交通大学）
Spin-orbit-entangled frustrated magnetism in fcc Ba$_2$(Yb,Nd)NbO$_6$ double perovskites
Shiv Nadar Institution of Eminence（Shiv Nadar卓越学院）；Bennett University（贝内特大学）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）；Indian Institute of Science Education and Research, Thiruvananthapuram（印度科学教育与研究研究所，特里凡得琅）；Japan Atomic Energy Agency（日本原子能机构）
Multiferroics with coupling between ferroelectricity and magnetism have been pursued for decades. However, their magnetoelectric performances remain limited due to the common trade-off between ferroelectricity and magnetism. Here, a family of nitride perovskites is proposed as multiferroics with prominent physical properties and nontrivial mechanisms. Taking GdWN$_3$ as a prototype, our first-principles calculations found that its perovskite phases own large polarizations (e.g. $111.3$ $μ$C/cm$^2$ for the $R3c$ phase) and a magnetic moment $7$ $μ_{\rm B}$/Gd$^{3+}$. More interestingly, its fer…
Lattice dynamics and structural correlations in antiferromagnet SrLaCoNbO$_6$ double perovskite
Ames National Laboratory, U.S. Department of Energy, Iowa State University（艾姆斯国家实验室）；Department of Physics, Indian Institute of Technology Delhi（德里印度理工学院物理系）；School of Physics, The University of New South Wales (UNSW)（新南威尔士大学物理学院）
The magnetic structures of rare-earth quadruple perovskite manganites $R$Mn$_7$O$_{12}$
本文报道了四元钙钛矿锰氧化物$R$ Mn $_7$ O $_{12}$的中子粉末衍射研究，其中$R$ = La，Ce，Nd，Sm，Eu。我们发现，在所有测量的化合物伴随的$A$和$B$锰亚晶格的磁有序发生在低于N $\mathrm{\acute{e}}$ EL温度冷却。相应的磁结构是共线的，如在体磁化测量中观察到的，每个公式单元具有一个未补偿的Mn $^{3+}$矩。结果表明，LaMn $_7$ O $_{12}$和NdMn $_7$ O $_{12}$在低温下都发生了第二次磁相变，这导致了$B$亚晶格磁矩的倾斜，这种倾斜在LaMn $_7$ O $_{12}$中是公度的，而在NdMn $_7$ O $_{12}$中是不公度的.这种自旋倾斜与源自$B$位置轨道顺序的磁不稳定性一致。此外，NdMn $_7$ O $_{12}$显示了第三个磁相变，在该第三个磁相变中，Nd亚晶格的长程有序改变了无公度自旋倾斜的周期性。我们的研究结果表明，过渡金属磁性，轨道顺序，和晶格，这可能是微调阳离子取代和稀土磁性之间的相互作用。
