Rh Substitution in

Dec 13, 2016 - Synopsis. The single-phase synthesis, characterizations, and magnetic properties of the new quaternary boride series FeRh6−nRunB3 (n ...
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Chemical Tuning of Magnetic Properties through Ru/Rh Substitution in Th7Fe3‑type FeRh6−nRunB3 (n = 1−5) Series Pritam Shankhari,† Patrick R. N. Misse,‡ Mohammed Mbarki,‡ Hyounmyung Park,† and Boniface P. T. Fokwa*,†,‡ †

Department of Chemistry, University of California Riverside, Riverside, California 92521, United States Institute of Inorganic Chemistry, RWTH Aachen University, D-52056 Aachen, Germany

‡

S Supporting Information *

ABSTRACT: The new quaternary boride series FeRh6−nRunB3 (n = 1−5) was synthesized by arc melting and characterized by powder and single-crystal X-ray diffraction (XRD), energy-dispersive X-ray analysis, and superconducting quantum interference device magnetometry. Single-crystal structure refinement showed the distribution of the iron atoms in two of three possible crystallographic 4d metal sites in the structure (Th7Fe3-type, space group P63mc). Rietveld refinements of the powder XRD data indicated singlephase synthesis of all the members. A linear decrease of the lattice parameters and the unit cell volume with increasing Ru content was found, indicating Vegard’s behavior. Susceptibility measurements show decreasing Curie temperature and magnetic moment (μa5T) recorded at 5 T with increasing Ru content from TC = 295 K and μa5T = 3.35 μB (FeRh5RuB3) to TC = 205 K and μa5T = 0.70 μB (FeRhRu5B3). The measured coercivities lie between 1.0 and 2.2 kA/m indicating soft to semihard magnetic materials.

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decreased anti-ferromagnetic interactions from 60 to 62 e−; then a transition from anti-ferromagnetism to ferromagnetism occurred between 62 and 63 e−. Adding more electrons (63−65 e−) further increased the ferromagnetic interactions in the series. These results were also confirmed by density functional theory (DFT) calculations.14 Unsurprisingly, all members of the series Ti2FeRu5−nRhnB2 (63−67 e−)12 were found to order ferromagnetically below their Curie temperatures. Interestingly, they provided the first semihard magnetic borides of transition metals with coercive field values (Hc) up to 23.9 kA/m (Hc values below 1 kA/m were recorded in the Sc2FeRu5−nRhnB2 series).11 Finally, using the 5d element iridium led to the series Sc2FeRu5−xIrB2, two members (with 62 and 63 e−) of which possess the highest coercivity measured for transition-metal borides so far, up to 52.4 kA/m.13 Motivated by the above-mentioned successful tuning of the magnetic properties of various itinerant magnets, we started similar investigations on boride series adopting the Th7Fe3 structure type. In the recently reported Crx(Rh1−yRuy)7−xB3 series, two distinct paramagnetic behaviors were found; while a Pauli paramagnetic state was observed in the Rh-rich side of the series, an additional temperature-dependent term in the Ru-rich side was present.15 These findings demonstrated that in the Th7Fe3 structure type, variation of the Ru/Rh content also has a significant impact on the magnetic properties in a given series, similar to the above-mentioned series with Ti3Co5B2-type

INTRODUCTION The non-centrosymmetric hexagonal Th7Fe3 structure (space group P63mc)1 is a versatile structure type that has drawn attention because of the interesting physical properties emanating from this particular structural arrangement. For example, giant magnetoresistance was found in Tb7Rh3,2 ferromagnetic transition was observed at 334 K in Gd7Pd3,3 and superconductivity was reported in the binary boride Ru7B3,4 just to name a few. Although some ternary boride phases of this structure type, containing magnetically active elements, were reported some 40 years ago such as Co0.77Re6.23B35 and Ni0.5Re6.5B3,6 magnetic ordering was found only recently through the discovery of the itinerant ferromagnetic ternary borides FeRh6B3 (TC = 240 K) and CoRh6B3 (TC = 150 K).7 In recent years, chemists have been increasingly interested in itinerant magnets, a traditional physicists’ research field, and by using rational synthetic tuning the magnetic properties of many materials could be drastically modified. For example, chemicalpressure-driven magnetic ordering changes were reported in Pr1−xEuxCo2P2 and ACo2As2 (A = Eu, Ca),8,9 and valence electron (VE)-dependent studies leading to different magnetic ordering phenomena have been studied in several series of compounds crystallizing with the prolific Ti3Co5B2-type structure.10−13 The latter studies focused on tuning the magnetic properties of boride series while maintaining the magnetically active element (Fe) constant: In the series Sc2FeRu5−nRhnB2 (n = 0−5, VE = 60−65 e−),11 gradually increasing the number of VE from 60 to 65 e− first resulted in © 2016 American Chemical Society

Received: September 28, 2016 Published: December 13, 2016 446

DOI: 10.1021/acs.inorgchem.6b02341 Inorg. Chem. 2017, 56, 446−451

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Inorganic Chemistry

= 7.450 (1) Å, c = 4.748 (1) Å),7 because Ru successively replaces the slightly larger Rh atoms. Throughout the series, as more rhodium is replaced by ruthenium, the lattice parameters and hence the cell volume decrease in a Vegard-like manner (Figure 1). In fact, the changes observed for the lattice parameter a are very small (0.009 Å in the entire series for a if compared to 0.042 Å for c), and no change at all for a is observed for the two Ru-richer phases (n = 4 and 5, see Figure 1). However, the lattice parameter c decreases greatly throughout the series (see above) and in a nearly linear manner; consequently, it dictates the behavior of the unit cell volume (see Figure 1, bottom). These findings are similar to the behaviors of the lattice parameters found in the isotypic CrRh6−nRunB3 series.15 Furthermore, the behaviors of a and c in these two series differ from those found in Ti3Co5B2-type series (e.g., Sc2FeRu5−nIrnB2), where both lattice parameters vary in opposite directions.13 These contrasting variations of the lattice parameters in series with these two structure types will surely have a direct influence on their magnetic behaviors (see Magnetism section below). Crystal Chemistry. Crystal Structure. A single crystal, found for the FeRh5RuB3 composition, allowed a detailed crystallographic study, the results of which have confirmed isotypism with Th7Fe3 structure type (space group P63mc, No. 186, Z = 2). Also, the same atom distribution as in the Rh-rich part of the CrRh6−nRunB3 series resulted,15 however, using iron instead of chromium. All relevant crystallographic data and experimental details of the data collection are given in Table 1.

structure. However, the two structure types are structurally completely different; thus, it is impossible to predict the impact of a Ru/Rh content variation in a magnetically ordered Th7Fe3type phase, for example, ferromagnetic FeRh6B3. The present work is, therefore, devoted to the new series FeRh6−nRunB3 (n = 1−5), for which we have investigated the impact on crystal structure and magnetism of a gradual Ru substitution for Rh in the itinerant ferromagnetic FeRh6B3.

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RESULTS AND DISCUSSION Phase Analysis and Structure Refinement. The phase analysis of each product within the FeRh6−nRunB3 (n = 1−5) series was conducted by Rietveld refinement of the powder Xray diffraction data. The refinements were based on the singlecrystal structure model of FeRh5RuB3 reported below, and all the peaks in each powder X-ray diffractogram could be assigned to the Th7Fe3 structure type (see Figure S1, Supporting Information). Thus, the compounds synthesized in this series were all single phases, and the presence of all metals in each composition were further confirmed by energy-dispersive X-ray (EDX) analysis (see spectrum in Figure S1 and Table S1, Supporting Information). The refinement results of all synthesized compositions are summarized in Table S2 (Supporting Information). The refined lattice parameters (a and c) of all compounds are listed in Table S1 (Supporting Information), and they have been plotted in Figure 1 as well. As expected, the lattice parameters of all quaternary members of the new series are smaller than those of the parent ternary compound FeRh6B3 (a

Table 1. Crystallographic and Single-Crystal Structure Refinement Data of Fe0.86Rh5.12Ru1.02B3 formula formula weight (g/mol) F(000) crystal size (mm3) θ-range (deg) hkl range

no. of reflections; Rint no. of independent reflections no. of obs. reflections I > 2σ(I) no. of parameters space group; Z cell parameters a (Å) c (Å) V (Å3) calculated density (g·cm−3) absorption coefficient μ (mm−1) GOF R1; wR2 (all I) difference peak/hole (e Å−3) CSD depository numbera

Fe0.86Rh5.12Ru1.02B3 703.42 618 0.08 × 0.06 × 0.04 5.34 ≤ θ ≤ 35.53° −12 ≤ h ≤ 8 −8 ≤ k ≤ 12 −7 ≤ l ≤ 7 2355; 0.0320 411 393 21 P63mc; 2 7.440(2) 4.7420(7) 227.30(6) 10.28 22.66 1.13 0.020; 0.032 1.074/−0.792 431 933

a

Additional crystallographic information is available in the Supporting Information.

Table 2 contains the atomic coordinates and the equivalent displacement parameters (see Supporting Information Table S2 for the anisotropic displacement parameters and Table S4 for selected interatomic distances). The lattice parameters obtained from the single-crystal measurement were found to be very close to those obtained from the powder analysis, indicating

Figure 1. Lattice parameters a and c (top) and unit cell volume V (bottom) as a function of ruthenium content (n) for the series FeRh6−nRunB3 (n = 1−5). 447

DOI: 10.1021/acs.inorgchem.6b02341 Inorg. Chem. 2017, 56, 446−451

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Inorganic Chemistry

trigonal prisms. Three (T1)3(T2)2T3 trigonal prisms are connected via three edges and a corner to form a T3-centered trigonal unit. Such trigonal units again connect to each other via corners and to the octahedral units via faces to finally form a three-dimensional structure. As found through structure refinement, iron is present in two (T2 and T3) of three metal sites in the FeRh6−nRunB3 series, a result that differs from the iron distribution in the parent FexRh7−xB3 (x ≤ 1) structure, where Fe was found only in one site (T2). Generally, for ternary phases with the formulas MxRh7−xB3 (M = Cr, Mn, Fe, Co, Ni) and MxRu7−xB3 (M = Mn, Fe, Co, Ni), there is a critical value of x (xc) below which M can occupy only the T2 site, and above xc M can occupy both T2 and T3 sites. As result, ternary Rh-rich phases have xc ≈ 1, while ternary Ru-rich phases have xc < 0.5.15−19 The series under investigation lies between these two scenarios, and Fe was found in both T2 and T3 sites but with a strong preference for the T2 site. Nevertheless, the presence of iron in two sites in the crystal structure of this new series differentiates it in terms of magnetism from the ternary ferromagnetic FeRh6B3 parent phase (see Magnetic section below). Chemical Bonding. Substituting Ru for Rh leads to gradual decrease of the unit cell volume as discussed above, and thus the overall bonding distances slightly decrease throughout the series, but they remain in the range observed for similar borides compounds.15−19 The metal−boron distances (see Table S4, Supporting Information) in the structure of Fe0.86Rh5.12Ru1.02B3 are the shortest ones, with an average value of 2.16 Å, which is very similar to that found in the Cr-based series Crx(Rh1−yRuy)7−xB3.15 Other ternary phases of the Th7Fe3 structure type, containing rhodium or ruthenium, have similar bond lengths.15−19 Using DFT calculations, these distances have been found to be the strongest in Th7Fe3-type ternary borides, but metallic interactions were found to also play a great role on their overall stability.20,21 The T2−T2 bonds (T2 = Ru/Rh/Fe, average 2.63 Å) are significantly shorter than all other metal−metal distances (>2.71 Å), because more Fe (smaller in size than rhodium and ruthenium) is present in the T2 site than in all other metal sites. The remaining metal− metal distances (T1−T1, T1−T2, T1−T3, or T2−T3, average 2.83 Å) are somewhat larger than the distances found in metallic rhodium (or ruthenium) for CN 12 (2.69 Å).23 However, they are short enough for bonding, and similar bonding distances have been found in other rhodium (or ruthenium) borides, such as in A2MRh5B2 with average Rh−Rh distances of 2.95 Å (A = Mg and Sc; M = main group and 3d elements)24 and in Sc2Ru5B4 with average Ru−Ru distances of 2.89 Å. Magnetism. The recently discovered first binary boride of a 3d transition metal with Th7Fe3 type of structure, metastable Ni7B3, was found to be paramagnetic, even though the phase is Ni-rich.25 This finding is in agreement with all ternary phases of this structure type studied until now and containing nickel as magnetically active element: Pauli paramagnetism was found in M0.5Ru6.5B3 (M = Cr, Mn, Co, Ni)16 and MxRh7−xB3 (M = Cr, Ni, x = 0.39−1),17 whereas temperature-dependent paramagnetism was observed in NiRh6B3 and Mn0.5Ru6.5B3. So far magnetic ordering has been found only in FeRh 6 B 3 (ferromagnetic, TC = 240 K) and CoRh6B3 (ferromagnetic, TC = 150 K).7 FeRh6B3 shows ferromagnetic behavior below 240 K and a large and positive Weiss constant θ = 238 K.7 Additionally, the role of rhodium atoms as mediators of long-range ferromag-

Table 2. Atomic Coordinates and Isotropic (Uiso for Boron) and Equivalent (Ueq) Displacement Parameters for Fe0.86Rh5.12Ru1.02B3a Wyckoff site occupation x, y, z Ueq (Å2) Wyckoff site occupation x, y, z Ueq (Å2) Wyckoff site occupation x, y, z Ueq (Å2) Wyckoff site occupation x, y, z Uiso (Å2)

Fe0.86Rh5.12Ru1.02B3 T1, 6c Rh1/Ru1 0.83:0.17 0.87519(3), 1 − x, 0.306 00(4) 0.0082(2) T2, 6c Rh2/Ru2/Fe2 0.614(6):0.123(2):0.263(7) 54 399(3), 1 − x, −0.0166(2) 0.0080(2) T3, 2b Rh3/Ru3/Fe3 0.77(1):0.16(2):0.07(2) 1/3, 2/3, −0.0158(2) 0.0070(2) B, 6c 1 0.1887(5), 0.8113(5), 0.214(2) 0.011(2)

a

Ueq is defined as 1/3 of the trace of the orthogonalized Uij tensors (see Supporting Information Table S2).

that the single-crystal composition should be very close to that of the bulk and thus also hints at its single-phase nature as found through Rietveld refinement. In the first steps of solving the crystal structure, three Wyckoff sites were identified for the transition metals {6c (T1 = Rh1/Ru1), 6c (T2 = Rh2/Ru2/Fe2), and 2b (T3 = Rh3/ Ru3/Fe3)}, and one site was found for boron (6c). We then assigned the Rh/Ru ratio obtained from the EDX data on all three sites (T1, T2, and T3). We found that two (T2 and T3) of these three sites had to be mixed with the lighter iron, due to their higher displacement parameters, which then became all nearly identical after iron insertion (see Table 2 and Table S3 in Supporting Information). The final composition was determined to be Fe0.86Rh5.12Ru1.02B3. Figure 2 shows a representative view of the crystal structure of the quaternary series FeRh6−nRunB3. The crystal structure is composed of two main building blocks: empty (T1)6 octahedra and the boroncentered (T1)3(T2)2T3 trigonal prisms. The (T1)6 octahedra are linked with each other via faces to form a one-dimensional string along the [001] direction perpendicular to the layer of

Figure 2. Projection of the crystal structure of the boride series FeRh6−nRunB3 along [001] highlighting the empty (T1)6 octahedra and the interconnected boron-filled [(T1)3(T2)2T3] trigonal prisms. T1 = Rh1/Ru1, T2 = Rh2/Ru2/Fe2, and T3 = Rh3/Ru3/Fe3. 448

DOI: 10.1021/acs.inorgchem.6b02341 Inorg. Chem. 2017, 56, 446−451

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Inorganic Chemistry netic interactions in this compound was shown by theoretical calculations.20,21 In contrast, the isotypical ruthenium-rich compound Fe0.5Ru6.5B3 shows predominantly anti-ferromagnetic interactions (θ = −74 K) and an overall ferrimagnetic behavior with TC ≈ 5 K.26 These findings indicate the different magnetic phenomena induced by either Ru or Rh in these phases. However, the fact that less iron is present in the Rubased ternary Fe0.5Ru6.5B3 implies22 that it is impossible to directly compare its magnetic behavior with those of the Fericher phases FeRh6B3 and the new series FeRh6−nRunB3. Furthermore, the crystal structures of these phases show different iron positions and occupations: while in FeRh6B3 only one iron position was found (T2); in Fe0.5Ru6.5B3 and FeRh6−nRunB3, however, two positions are observed (T2 and T3, with a strong preference of iron for T2). A consequence of this compositional and structural analysis is that all three systems should have distinct magnetic behaviors. Nevertheless, a gradual substitution of a magnetically “inactive” element (Rh) by another (Ru) in the FeRh6−nRunB3 series has drastic effects on the magnetic properties in this series. The magnetic measurements reported in this work (see Figures 3 and 4 as well as Figure S2 in Supporting Information)

Figure 4. Hysteresis loops for all members of the series FeRh6−nRunB3 (n = 1−5) at 5 K.

Table 3. Curie Temperature (TC), Weiss Constant (Θ), Coercive Force (Hc), and Largest Measured Magnetic Moment (μa5T, at 5 T) Obtained at B0 = 0.01 T for the Series FeRh6−nRunB3 (n = 1−5) with 70−66 Valence Electrons (VE)

a

formula

VE

TC (K)

Θ (K)

Hc (kA/m)

μa5T (μB)a

FeRh5RuB3 FeRh4Ru2B3 FeRh3Ru3B3 FeRh2Ru4B3 FeRhRu5B3

70 69 68 67 66

295(10) 285(10) 275(15) 250(10) 205(30)

290(15) 325(15) 350(10)

2.2 1.6 1.6 1.0 1.9

3.35 2.54 1.96 1.10 0.70

Magnetic moment at B0 = 5 T.

The 1/χm − T curves show two distinct behaviors in the series. While for the rhodium-rich members (n = 1−3) Curie− Weiss-like behavior is found at high temperatures (see, e.g., Figure 3, bottom), for the two ruthenium-rich members no Curie−Weiss behavior was found. Extrapolations of the Curie− Weiss lines for the rhodium-rich members give large and positive Weiss constants (θ) in all cases (see Table 3), indicating the presence of strong ferromagnetic interactions. All Weiss constants are very close to each other, between 290 and 350 K, indicating similarly strong ferromagnetic interactions in this rhodium-rich part of the series. The extrapolated Curie temperatures (see Figure 3 top, as well as Figure S2 in Supporting Information) are found to be also very close to each other in the Rh-rich part of the series, between 275 and 295 K (see Table 3), thus confirming the similar nature of the ferromagnetic interactions in this region. In the ruthenium-rich part, however, smaller TC values were found (250 and 205 K) indicating weaker ferromagnetic interactions. Generally, decreasing Curie temperature with increasing Ru content (or decreasing valence electrons) is found in the series. On the basis of the above-discussed Curie temperature (TC), the Rh-richer side of the series has greater ferromagnetic interactions than the Ru-richer side, and a decrease of TC with increasing Ru content was found. Field-dependent studies reveal a similar behavior; in fact, the measured hysteresis (see Figure 4) saturates for n = 1 already at 4 T, but for n = 2 and 3 no saturation is reached until 5 T, and the degree of hysteresis unsaturation increases with increasing Ru content. Furthermore, a linear decrease of the largest magnetic moment recorded at 5 T and 5 K is observed throughout the series (see Figure 5). This magnetic behavior may be understood by assuming canting of the magnetic spins on the iron atoms: If the canting angle increases with increasing ruthenium content

Figure 3. Magnetic moment vs temperature (top, μa − T diagram) and inverse susceptibility vs temperature (bottom, 1/χm − T diagram) for FeRh3Ru3B3 at B0 = 0.01 T. The obtained Curie temperature is TC ≈ 275 K (top), and the Weiss constant is θ ≈ 350 K (bottom). The dashed line indicates the Curie−Weiss behavior.

were performed using a superconducting quantum interference device (SQUID) magnetometer in the temperature range from 2 to 400 K and at an applied magnetic field of B0 = 0.01 T. In addition, a hysteresis loop in the field range of ±5 T was measured at a temperature of 5 K for each compound. Table 3 summarizes the obtained magnetic quantities. 449

DOI: 10.1021/acs.inorgchem.6b02341 Inorg. Chem. 2017, 56, 446−451

Inorganic Chemistry

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CONCLUSIONS

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EXPERIMENTAL SECTION

The new quaternary boride series FeRh6−nRu3B3 (n = 1−5) has been successfully synthesized and characterized by powder and single-crystal X-ray diffraction as well as EDX analysis and SQUID magnetometry. The refined unit cell volume decreases linearly with increasing ruthenium content. Single-crystal X-ray diffraction proved the presence of iron on two out of three available Ru/Rh sites, and the Rietveld structure refinements of all members of the series confirmed isotypism with the noncentrosymmetric Th7Fe3-type structure. Temperature-dependent as well as field-dependent magnetic measurements revealed the presence of significant ferromagnetic interactions in all members of the series; however, the Rh-rich side shows significantly higher Curie temperatures and magnetic moments than the Ru-rich part. Furthermore, a linear decrease of the magnetic moment with increasing ruthenium content is found. The measured coercivity forces indicate soft to semihard magnetic materials.

Figure 5. Measured magnetic moment (at 5 T and 5 K) plotted against the ruthenium content (n) in FeRh6−nRu3B3 (n = 1−5). The dashed line shows the linear dependency of the magnetic moment with respect to n.

in the series, it would explain the weaker spin interactions and the difficulty to reach saturation at high Ru content. However, neutron diffraction studies will be needed to verify this assumption, provided large amount of polycrystalline powder samples of good quality (or large single crystals) can be synthesized and the magnetic structure can be solved. Such studies are planned. As shown above, the Ru/Rh substitution has a drastic influence on the magnetic properties in the new series FeRh6−nRu3B3 (n = 1−5); however, the here-found evolution of the magnetic properties is completely different from that found in other previously reported boride series. In all series of the Ti3Co5B2 structure type studied until now, a linear variation of the magnetic moment or Curie temperature throughout the series has never been observed, even though a clear decrease of the magnetic moment with increasing Ru content was also found.11−13 These contrasting results are the consequence of the different behaviors of the lattice parameters in series of these two structure types: In fact, in the here-reported series, both lattice parameters decrease with increasing Ru content, whereas in series with Ti3Co5B2 structure type the lattice parameters vary in opposite direction. Nevertheless, in both series, greater ferromagnetic interactions are found in the Rhrich side and weaker in the Ru-rich one. Per a theoretical analysis on the Ti3Co5B2-type Sc2FeRh5−xRuxB2 series some years ago,14 the magnetic exchange coupling JRh−Fe was found to be significantly higher than JRu−Fe, leading to greater ferromagnetic interactions and higher magnetic moment on Fe atoms in the Rh-rich side of the series and predominantly anti-ferromagnetic interactions and smaller magnetic moments in the Ru-based side. We expect a similar mechanism in the present series. The measured coercive forces of all members have values between 1 kA/m and 2.2 kA/m. These values are in the same range as those recorded previously for the isotypic ferromagnets FeRh6B3 (2.1 kA/m) and CoRh6B3 (1.7 kA/ m).7 However, no real coercivity trend is apparent in the new series, which is in strong contrast with behaviors found in other boride series (Ti2FeRu5−nRhnB2 and Sc2FeRu5−nIrnB2), where drastic increase of the coercive force with increasing ruthenium content has been found.12,13 This is another great example of structure−property-based relationships. On the basis of the recorded coercive forces, the members of the new series FeRh6−nRu3B3 (n = 1−5) may be classified as soft to semihard magnetic materials.

Synthesis. The compounds of the series FeRh6−nRunB3 (n = 1−5) were synthesized by arc-melting pelletized powders of the elemental components in the appropriate stoichiometric ratio under argon atmosphere. The starting materials used for the synthesis were powders of cobalt (99.99%, Alfa Aesar), iron (99.99%, Alfa Aesar), rhodium (100% UMICORE AG & Co. KG, Hanau), and boron (amorphous 97%, ABCR; or crystalline pieces, 99.999%, Alfa Aesar). The argon gas was purified prior to use over silica gel, molecular sieves, and titanium sponge (at 950 K). The elements were weighed in the respective atomic ratios with a total mass of ∼0.3 g and were pressed into pellets. Each synthesis was performed on a water-cooled copper crucible using a tungsten tip as the second electrode, where the pellet was melted for several seconds by an electric arc plasma with a direct current of 40 A until a homogeneous melting was achieved. The reaction product was remelted several times to ensure good homogeneity of the sample. Weight losses during the melting process were negligible. The obtained metallic shiny regulus was mechanically cracked apart and pulverized for characterization using a mortar and a pestle. The samples are stable in air as a compact bulk as well as finely ground powders. Powder X-ray Diffraction and EDX analysis. Powder diffraction methods were applied for the phase identification and the determination of lattice parameters at room temperature, using a powder diffractometer [STOE Stadi P, transmission geometry; Cu Kα1 radiation (λ = 1.540 59 Å), Ge monochromator, image plate detector, and silicon as standard]. The lattice parameters were indexed and refined with the WinXPOW program. The recorded powder X-ray diffractograms were refined by means of the Rietveld method (fullmatrix least-squares refinement) as implemented in the FULLPROF program suite.27 The X-ray data of a single crystal of FeRh5RuB3 were collected at room temperature on a CCD single-crystal diffractometer (Bruker SMART APEX) with graphite-monochromatized Mo Kα radiation (λ = 0.710 73 Å). The X-ray intensities were corrected with respect to absorption using a semiempirical procedure.28 The crystal structure was solved by means of direct method and refined by full-matrix leastsquares refinement (based on F2) using anisotropic displacement parameters for the metals and isotropic one for boron.29 The compositions were analyzed by semiquantitative EDX on a high-resolution low-energy SEM of the type LEO 1530 (Oberkochen, Germany) equipped with an EDX system of the type INCA (Oxford, England). Magnetic Measurements. Temperature-dependent susceptibility data on the compounds FeRh6−nRunB3 (n = 1−5) were recorded with a SQUID magnetometer (MPMS-XL5, Quantum Design) in the temperature range from 2 to 400 K and at a field of up to 5 T. Details concerning sample arrangement and measurement technique are 450

DOI: 10.1021/acs.inorgchem.6b02341 Inorg. Chem. 2017, 56, 446−451

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Inorganic Chemistry described elsewhere, and the interpretation of the magnetic data followed the recommendations of Hatcher et al.30

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02341. X-ray crystallographic information (CIF) Rietveld refinement plot, magnetic moment versus temperature plot, semiquantitative EDX analysis, Rietveld refinement results, anisotropic displacement parameters, interatomic distances of FeRh5RuB3 (PDF) Further details of the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax: +49-7247-808-666; E-Mail: crysdata@fiz-karlsruhe.de).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Boniface P. T. Fokwa: 0000-0001-9802-7815 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Deutsche Forschungsgemeinschaft and UC Riverside (startup fund to B.P.T.F.) for financial support. REFERENCES

(1) Malik, S. K.; Wallace, W. E.; Takeshita, T. Hydrogen induced change from superconducting to magnetically ordered state in Th7Fe3. Solid State Commun. 1978, 28, 359. (2) Sengupta, K.; Iyer, K. K.; Sampathkumaran, E. V. Magnetic and magnetoresistance behavior of Tb7Rh3, an intermetallic compound with a negative temperature coefficient of electrical resistivity in the paramagnetic state. Solid State Commun. 2006, 139, 351. (3) Talik, E.; Klimczak, M.; Troć, R.; Kusz, J.; Hofmeister, W.; Winiarski, A. Comparison of magnetic and transport properties of Gd6YPld3 and Gd7Pd3 single crystals. J. Alloys Compd. 2008, 460, 1. (4) Kase, N.; Akimitsu, J. Superconducting State of the Binary Boride Ru7B3 with the Noncentrosymmetric Crystal Structure. J. Phys. Soc. Jpn. 2009, 78, 044710. (5) Chepiga, M. V.; Kuz’ma, Y. B. The system rhenium-cobalt boron. Inorg. Mater. 1973, 9, 1505. (6) Chepiga, M. V. Rhenium-nickel-boron system. Lviv. Serzh. Univ. (ser. Khim.) 1972, 14, 27. (7) Misse, P. R. N.; Gilleßen, M.; Fokwa, B. P. T. Site-Preferential Design of Itinerant Ferromagnetic Borides: Experimental and Theoretical Investigation of MRh6B3 (M = Fe, Co). Inorg. Chem. 2011, 50, 10303. (8) Kovnir, K.; Reiff, W. M.; Menushenkov, A. P.; Yaroslavtsev, A. A.; Chernikov, R. V.; Shatruk, M. Chemical Metamagnetism”: From Antiferromagnetic PrCo2P2 to Ferromagnetic Pr0.8Eu0.2Co2P2 via Chemical Compression. Chem. Mater. 2011, 23, 3021. (9) Tan, X.; Fabbris, G.; Haskel, D.; Yaroslavtsev, A. A.; Cao, H. B.; Thompson, C. M.; Kovnir, K.; Menushenkov, A. P.; Chernikov, R. V.; Garlea, O. V.; Shatruk, M. A Transition from Localized to Strongly Correlated Electron Behavior and Mixed Valence Driven by Physical or Chemical Pressure in ACo2As2 (A = Eu and Ca). J. Am. Chem. Soc. 2016, 138, 2724. (10) Fokwa, B. P. T. Transition-Metal-Rich Borides − Fascinating Crystal Structures and Magnetic Properties. Eur. J. Inorg. Chem. 2010, 2010, 3075. 451

DOI: 10.1021/acs.inorgchem.6b02341 Inorg. Chem. 2017, 56, 446−451