Contrasting Magnetism in Isovalent Layered LaSr$_{3}$NiRuO$_{4}$H$_{4}$ and LaSrNiRuO$_{4}$ due to Distinct Spin-Orbital States
Xuan Wen1, Ke Yang1, Hua Wu1,2**
1Laboratory for Computational Physical Sciences (MOE), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433 2Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093
Abstract：The recently synthesized first $4d$ transition-metal oxide-hydride LaSr$_{3}$NiRuO$_{4}$H$_{4}$ with the unusual high H:O ratio surprisingly displays no magnetic order down to 1.8 K. This is in sharp contrast to the similar unusual low-valent Ni$^{+}$-Ru$^{2+}$ layered oxide LaSrNiRuO$_{4}$ which has a rather high ferromagnetic (FM) ordering Curie temperature $T_{\rm C}\sim 250$ K. Using density functional calculations with the aid of crystal field level diagrams and superexchange pictures, we find that the contrasting magnetism is due to the distinct spin-orbital states of the Ru$^{2+}$ ions (in addition to the common Ni$^{+}$ $S=1/2$ state but with a different orbital state): the Ru$^{2+}$ $S=0$ state in LaSr$_{3}$NiRuO$_{4}$H$_{4}$, but the Ru$^{2+}$ $S=1$ state in LaSrNiRuO$_{4}$. The Ru$^{2+}$ $S=0$ state has the $(xy)^2(xz,yz)^4$ occupation due to the RuH$_4$O$_2$ octahedral coordination, and then the nonmagnetic Ru$^{2+}$ ions dilute the $S=1/2$ Ni$^+$ sublattice which consequently has a very weak antiferromagnetic superexchange and thus accounts for the presence of no magnetic order down to 1.8 K in LaSr$_{3}$NiRuO$_{4}$H$_{4}$. In strong contrast, the Ru$^{2+}$ $S=1$ state in LaSrNiRuO$_{4}$ has the $(3z^2-r^2)^2(xz,yz)^3(xy)^1$ occupation due to the planar square RuO$_4$ coordination, and then the multi-orbital FM superexchange between the $S=1/2$ Ni$^+$ and $S=1$ Ru$^{2+}$ ions gives rise to the high $T_{\rm C}$ in LaSrNiRuO$_{4}$. This work highlights the importance of spin-orbital states in determining the distinct magnetism.
(Electron density of states and band structure of crystalline solids)
引用本文:
. [J]. 中国物理快报, 2019, 36(7): 77501-.
Xuan Wen, Ke Yang, Hua Wu. Contrasting Magnetism in Isovalent Layered LaSr$_{3}$NiRuO$_{4}$H$_{4}$ and LaSrNiRuO$_{4}$ due to Distinct Spin-Orbital States. Chin. Phys. Lett., 2019, 36(7): 77501-.
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2019, Vol. 36 
