Contrasting Magnetism in Isovalent Layered LaSr3NiRuO4H4 and LaSrNiRuO4 due to Distinct Spin-Orbital States
Abstract
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.
- Publication:
-
Chinese Physics Letters
- Pub Date:
- July 2019
- DOI:
- 10.1088/0256-307X/36/7/077501
- arXiv:
- arXiv:1905.10055
- Bibcode:
- 2019ChPhL..36g7501W
- Keywords:
-
- 75.25.Dk;
- 71.70.-d;
- 71.20.-b;
- Condensed Matter - Strongly Correlated Electrons;
- Condensed Matter - Materials Science
- E-Print:
- 6 pages, 4 figures, 1 table