摘要
The recently synthesized first 4d transition-metal oxide-hydride LaSr3NiRuO4H4 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 LaSrNiRuO4 which has a rather high ferromagnetic(FM) ordering Curie temperature TC^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 LaSr3NiRuO4H4, but the Ru^2+S= 1 state in LaSrNiRuO4. The Ru^2+S = 0 state has the(xy)^2(xz, yz)^4 occupation due to the RuH4O2 octahedral coordination, and then the nonmagnetic Ru2+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 LaSr3NiRuO4H4. In strong contrast, the Ru^2+S = 1 state in LaSrNiRuO4 has the(3z^2-r^2)^2(xz, yz)^3(xy)^1 occupation due to the planar square RuO4 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 TC in LaSrNiRuO4. This work highlights the importance of spin-orbital states in determining the distinct magnetism.
The recently synthesized first 4d transition-metal oxide-hydride LaSr3NiRuO4H4 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+-Ru2+ layered oxide LaSrNiRuO4 which has a rather high ferromagnetic（FM） ordering Curie temperature TC～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 Ru2+ions（in addition to the common Ni+S = 1/2 state but with a different orbital state）: the Ru2+S = 0 state in LaSr3NiRuO4H4, but the Ru2+S= 1 state in LaSrNiRuO4. The Ru2+S = 0 state has the（xy）2（xz, yz）4 occupation due to the RuH4O2 octahedral coordination, and then the nonmagnetic Ru2+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 LaSr3NiRuO4H4. In strong contrast, the Ru2+S = 1 state in LaSrNiRuO4 has the（3z2-r2）2（xz, yz）3（xy）1 occupation due to the planar square RuO4 coordination, and then the multi-orbital FM superexchange between the S= 1/2 Ni+ and S= 1 Ru2+ions gives rise to the high TC in LaSrNiRuO4. This work highlights the importance of spin-orbital states in determining the distinct magnetism.
作者
Xuan Wen
Ke Yang
Hua Wu
文轩;杨柯;吴骅(Laboratory for Computational Physical Sciences (MOE), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433;Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093)
基金
Supported by the National Natural Science Foundation of China under Grant Nos 11674064 and 11474059
the National Key Research and Development Program of China under Grant No 2016YFA0300700
