Rational Synthetic Tuning between Itinerant Antiferromagnetism and Ferromagnetism in the Complex Boride Series Sc₂FeRu_5−nRh_nB₂ (0≤n≤5)

Abstract

Single crystals of the complex boride series Sc(2)FeRu(5-n)Rh(n)B(2) (n=1, 3, 4) were synthesized by arc-melting the elements in water-cooled copper crucibles under argon atmospheres and were chemically characterized by single-crystal XRD and EDX analyses. The new compounds are isotypic and crystallize in the tetragonal space group P4/mbm with Z=2, adopting a substitutional variant of the Ti(3)Co(5)B(2)-type structure. The magnetically active iron atoms are arranged in chains with intra- and interchain distances of about 3.02 and 6.60 A, respectively. Strong ferromagnetic interactions are observed for both Sc(2)FeRuRh(4)B(2) (64 valence electrons (VE), TC approximately 350 K, mu(a)=3.1 mu(B)) and Sc(2)FeRu(2)Rh(3)B(2) (63 VE, T(C) approximately 300 K, mu(a)=3.0 mu(B)), whereas antiferromagnetic interactions are found in the case of Sc(2)FeRu(4)RhB(2) (61 VE, T(N) approximately 10 K, mu(eff)=3.2): The magnetism of the entire Sc(2)FeRu(5-n)Rh(n)B(2) (0<or=n<or=5) series is discussed based on the variable valence-electron count and the resulting Fe-Fe bonding character, and it is also compared with other isoelectronic systems.

Rational Design of Complex Borides – One‐Electron‐Step Evolution from Soft to Semi‐Hard Itinerant Ferromagnets in the New Boride Series Ti2FeRu5–nRhnB2(1 ≤n≤ 5)

“…[17] As mentioned in the Introduction already, upon varying the VEC in series 1 from 60 to 65, the stepwise change of long-range magnetic ordering from strong antiferromagnetism (VEC = 60) to strong ferromagnetism (VEC = 65) was observed together with an increase of the magnetic saturation moment in the ferromagnetic range. [12] The substitution of scandium in series 1 by titanium to produce series 2 leads to a shifting of the VEC range from VEC = 60-65 in the first to VEC = 63-67 in the second (the 62 VE phase was not achieved in series 2). Therefore, both series overlap in the VEC range VEC = 63-65, which corresponds to the ferromagnetic range in series 1.…”

“…Magnetic values for series 2 (Ti 2 FeRu 5-n Rh n B 2 ). the trend in lattice dimensions of the isoelectronic species of series 1 (n = 3, 4, 5 [12] ) and of the isotypic solid solutions Sc 1-x Si x Ir 5 B 2 [9] Figure S1) when keeping the volume nearly constant at approximately 248 Å 3 (see Table 2). Single-crystal structure analyses of all members of series 2 confirmed the order of titanium, iron, and boron atoms on their respective positions as well as the order of rhodium in the case of Ti 2 FeRh 5 B 2 .…”

“…For more details, see synthesis of series 1. [12] According to powder X-ray diffractograms, all ruthenium-rich phases and Ti 2 FeRu 2 Rh 3 B 2 are single-phase, but Ti 2 FeRuRh 4 B 2 and Ti 2 FeRh 5 B 2 are slightly contaminated by the Ti 2 Rh 6 B phase. As it is almost impossible to differentiate rhodium and ruthenium in the same compound by means of X-ray diffraction (they differ from each other by just one electron), the Ru/Rh ratio was very well characterized by energy dispersive X-ray analysis (EDX) with a high-resolution, low-energy SEM of the type LEO 1530 (Oberkochen, Germany) equipped with an EDX system of the type INCA (Oxford, England).…”

“…As it is almost impossible to differentiate rhodium and ruthenium in the same compound by means of X-ray diffraction (they differ from each other by just one electron), the Ru/Rh ratio was very well characterized by energy dispersive X-ray analysis (EDX) with a high-resolution, low-energy SEM of the type LEO 1530 (Oberkochen, Germany) equipped with an EDX system of the type INCA (Oxford, England). EDX measurements on several selected crystals provided the same Fe/Ti ratio (1:2.07) for all compounds: [12] were used as starting models for the structure refinements, [19] replacing Sc by Ti (Table 2). When these starting models are used, the refinements converge rapidly.…”

“…The first set of compounds which has enabled a truly chemical fine-tuning of the magnetic properties was Sc 2 FeRu 5-n Rh n B 2 (series 1) where n = 0, 1, ..., 5 with respective VEC = 60, 61, ..., 65. [12] The phases of series 1 differ exclusively in the ratio of the magnetically "silent" metals Ru and Rh. Upon varying the VEC from 60 to 65, that is, with increasing Rh content, the stepwise change of long-range magnetic ordering from strong antiferromagnetism (VEC = 60) to strong ferromagnetism (VEC = 65) was observed together with an increase in the magnetic saturation moment in the ferromagnetic range.…”