A Delicate Balance between Antiferromagnetism and Ferromagnetism: Theoretical and Experimental Studies of A 2 MRu 5 B 2 (A=Zr, Hf; M=Fe, Mn) Metal Borides

• Published in: Chemistry : a European journal Vol. 26; no. 9; pp. 1979 - 1988
• Main Authors: Shankhari, Pritam, Bakshi, Nika G, Zhang, Yuemei, Stekovic, Dejan, Itkis, Mikhail E, Fokwa, Boniface P T
• Format: Journal Article
• Language: English
• Published: Germany 11-02-2020
• Subjects: density functional theory (DFT); Ti3Co5B2-type structure; borides; antiferromagnetism; ferromagnetism
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201904572

Metal-rich borides with the Ti
Co
B
-type structure represent an ideal playground for tuning magnetic interactions through chemical substitutions. In this work, density functional theory (DFT) and experimental studies of Ru-rich quaternary borides with the general composition A
MRu
B
(A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr
FeRu
B
and Hf
FeRu
B
prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M-chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically and creates a strong competition between FM and AFM states with a slight preference for AFM in Zr
MnRu
B
and for FM in Hf
MnRu
B
. Magnetic property measurements show a field dependence of the AFM transition (T
): T
is found at 0.1 T for all phases with predicted AFM states whereas for the predicted FM phase it is found at a much lower magnetic field (0.005 T). Furthermore, T
is lowest for a Hf-based phase (20 K) and highest for a Zr-based one (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf-based phases. Interestingly, the AFM transitions vanish in all compounds at higher fields (>1 T) in favor of FM transitions, indicating metamagnetic behaviors for these Ru-rich phases.