Metamagnetic transitions induced by doping with non-magnetic 4+ions in ludwigites Co5A(O2BO3)2 (A=Zr and Hf)

The novel A-doped Co3O2BO3 (A(4+)=Zr, Hf) ludwigites have been synthetized by the first time and investigated by X-ray diffraction, magnetization and specific heat experiments. The non-magnetic ions place mainly at sites 4 of the structure. This doping strengthens the magnetic interactions rising the magnetic transition temperatures from 42 K, for the undoped compound, to 71 K and 72 K for Zr and Hf, respectively. These magnetic transition temperature are 10 K below that shown by the Sn4+-doped Co3O2BO3. As expected, all these isostructural and isovalent compounds exhibit the same magnetic features. However, low temperature specific heat experiments and magnetization curves with typical metamagnetic behavior revealed that doping with the non-magnetic open-shell ions d(0) Zr and Hf preserves the two-dimensional antiferromagnetic character of the parent ludwigite Co3O2BO3 while the closed-shell d(10 )Sn leads to a three-dimensional magnetism. The experimental results are compatible with an antiferromagnetic structure with a ferromagnetic component for these two compounds. The difference in T-N and dimensionality of these compounds are related to super-superexchange (SSE) interaction between two Co2+ mediated by the nonmagnetic ion A(4+). The non-magnetic closed-shell d(10) ion turned out to be more effective in mediating SSE interactions between 1-2-3 magnetic layers. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The novel A-doped Co3O2BO3 (A(4+)=Zr, Hf) ludwigites were synthesized for the first time and found to exhibit different magnetic properties and dimensions depending on the dopant ion used. Doping with non-magnetic ions Zr and Hf preserved the two-dimensional antiferromagnetic character, while Sn led to three-dimensional magnetism. The experimental results suggest an antiferromagnetic structure with a ferromagnetic component for Zr and Hf dopants.