A Delicate Balance between Antiferromagnetism and Ferromagnetism: Theoretical and Experimental Studies of A₂MRu₅B₂ (A=Zr, Hf; M=Fe, Mn) Metal Borides

Abstract

Metal-rich boridesw ith the Ti 3 Co 5 B 2 -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 boridesw ith the general composition A 2 MRu 5 B 2 (A = Zr,H f, M = Fe, Mn) are presented.T otal energy calculations show that the phases Zr 2 FeRu 5 B 2 and Hf 2 FeRu 5 B 2 prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M-chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically andcreates astrong competition between FM and AFM states with as light preference for AFM in Zr 2 MnRu 5 B 2 andf or FM in Hf 2 MnRu 5 B 2 .M agnetic property measurements show af ield dependence of the AFM transition (T N ): T N is found at 0.1 Tf or all phases with predicted AFM states whereasf or the predicted FM phase it is found at am uch lower magneticf ield (0.005 T). Furthermore, T N is lowest for aH f-based phase (20 K) and highest for aZ r-basedo ne (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf-based phases.I nterestingly,t he AFM transitions vanish in all compounds at higherf ields (> 1T)i nf avor of FM transitions, indicating metamagnetic behaviors for these Ru-richphases.[a] Dr.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Rare-Earth-Free Magnets: Enhancing Magnetic Anisotropy and Spin Exchange Toward High-TC Hf2MIr5B2 (M = Mn, Fe)

“…Consequently, the similarity in stabilization energies confirms that these interchain interactions are rather weak, thus they can easily be affected by external stimuli such as magnetic field or pressure. This finding corroborates our recent report on the Ru-based series A 2 M Ru 5 B 2 ( A = Zr, Hf and M = Fe, Mn), the magnetic orderings of which were found to be highly magnetic-field-dependent. While the predicted FM ground state is in perfect agreement for Hf 2 FeIr 5 B 2 , if compared with previously reported Ti 3 Co 5 B 2 -type compounds (Table S2), AFM1 is somewhat unexpected for Hf 2 MnIr 5 B 2 .…”

“…In fact, AFM1 is mostly preferred in Fe-based Ru-rich compounds with 63 VE or fewer, while FM is more stable for phases that are richer in group-9-elements (Co, Rh, and Ir) and have 63 VE or more. Examples of calculated AFM1 compounds include: Sc 2 FeRu 5– n Ir n B 2 ( n = 0–2; 60–62 VE), Zr 2 FeRu 5 B 2 (62 VE), Hf 2 FeRu 5 B 2 (62 VE), Ti 2 FeRu 4 RhB 2 (63 VE), and Sc 2 FeRu 3 Ir 2 B 2 (62 VE), while the calculated FM compounds are Sc 2 FeRu 5– n Ir n B 2 ( n = 3–5; 63–65 VE), Hf 2 FeIr 5 B 2 (67 VE, present work), Ti 2 FeRh 5 B 2 (67 VE), Ti 2 FeCo 5 B 2 (67 VE), and Hf 2 FeCo 5 B 2 (67 VE) …”

Triangular Arrangement of Ferromagnetic Iron Chains in the High‐TC Ferromagnet TiFe1−xOs2+xB2

“…Typically, selective substitution is utilized to introduce magnetic 3 d elements into existing crystal structures that lack them. Recent examples include the Nb 7 Ir 6 B 8 and Hf 3 Ir 5 B 2 structures, where the substitution of an early transition metal by a magnetic 3 d element M (Mn or Fe) has respectively led to M ‐chains in Nb 6 M 1− x Ir 6+ x B 6 [11] and Hf 2 M Ir 5 B 2 , [12–14] thereby producing ferromagnetic (and ferrimagnetic) orderings with Curie temperatures near or above room temperature. Different chains of magnetic elements were discovered in Ti 9 Fe 2 Ru 18 B 8 (Fe ladder) [15] and in TiCrIr 2 B 2 (chain of Cr 3 ‐triangles) [16] .…”

The First Quaternary Phase of the NbRuB Structure Type: Experimental and Computational Investigations of TiFe1.3Os3.9B2.8

“…Interestingly, the FM model is only 13 meV less stable than the AFM model. Considering recent studies such as A 2 MRu 5 B 2 (A = Zr, Hf; M = Mn, Fe), [25] Ti 5-x Fe 1-y Os 6 + x + y B 6 [13] and TiFe 1-x Os 2 + x B 2 , [20] where such small energy differences were also found between the same types of AFM and FM models, and that in many cases a variation in either the external magnetic field or the composition led to ferromagnetic ordering being favored experimentally, it is likely that our synthesized phase could be dominated by ferromagnetic interactions as the mixed occupations observed experimentally and involving Fe could not be modeled theoretically. Furthermore, the experimental composition, TiFe 1.3 Os 3.9 B 2.8 , has 108 valence electrons (VE) per unit cell, i. e. 2 VE more than the ideal composition (TiFeOs 4 B 3 used for calculations), which assuming a valid rigid band model would shift the Fermi energy (E F ) by + 0.12 eV (Figure 3, red dashed line).…”