Itinerant Electron Metamagnetism in η-Carbide-Type Compound Co₃Mo₃C

Abstract

We report the magnetic properties of the cobalt molybdenum -carbide-type compounds Co 3 Mo 3 C and Co 3 Mo 3 N. The magnetic susceptibility of Co 3 Mo 3 C shows a Curie-Weiss temperature dependence at high temperatures and a broad maximum at around 100 K, whereas that of Co 3 Mo 3 N shows a nearly temperature-independent enhanced Pauli paramagnetic behavior. The absence of a magnetic long-range order was confirmed by the nuclear magnetic resonance technique in both the compounds. As expected from the broad maximum of , we observed an itinerant electron metamagnetic transition at around 37 T in Co 3 Mo 3 C.Ternary transition-metal interstitial compounds M 3 M 0 3 X (M: 3d transition metal, M 0 : 4d, 5d transition metal of early groups) are known to have the -carbide-type structure with the cubic space group Fd " 3 3m (227). Because of their hardness and catalytic ability, -carbide-type compounds have been studied for about half a century from a technological viewpoint. However, their electronic properties were less studied. In the structure, M, M 0 , and X atoms occupy the Wyckoff positions 16d/32e, 48f, and 16c, respectively. Focusing on M, which is expected to contribute mainly to the magnetic properties of the system, the 16d/32e sites form a three-dimensional (3D) network of the stella quadrangula (SQ) lattice. 1) SQ is a polyhedron as each face of a tetrahedron composed of 32e atoms is capped with another tetrahedron whose extra apex is a 16d atom. Because the SQ lattice is composed of tetrahedrons, magnetic properties are interesting from the aspect of geometrical frustration. Recently, we have reported a non-Fermi-liquid behavior in pure Fe 3 Mo 3 N without any tuning of pressure or concentration. 2) The magnetic properties of isostructural compounds are also expected to be of a wide variety.The synthetic routes of cobalt molybdenum -carbidetype compounds Co 3 Mo 3 X (X ¼ C, N) have been studied well. Co 3 Mo 3 N was first synthesized by Houmes et al. by ammonolysis of oxide precursors. 3) Following them, several methods of the reduction and nitridation of oxide precursors such as the plasma method 4) and urea method 5) have been reported. The resistivity shows a metallic behavior 5,6) and the magnetic susceptibility is of a Pauli paramagnet. 4,7) A superparamagnetic behavior and the absence of a magnetic long-range order were also suggested. 7) Although Co 3 Mo 3 C was first made by arc melting of elements, more moderate methods have been developed to avoid the excess occupation of Mo atoms of the 16d site. 8,9) Typical methods are reduction by H 2 and successive CO/CO 2 buffered gas treatment with cobalt tris(ethylenediamine) molybdate, 10)

Itinerant electron magnetism of η-carbides Co6M6C and Ni6M6C (M = Mo and W)

“…However their detailed electronic properties remain to be investigated. Recently, a wide variety of magnetic properties of η-6 have been reported by our group [4,5,6,7] and others [8,9,10,11,12,13,14]. For example, we have found that Fe 3 Mo 3 N show a non-Fermi-liquid behavior at low temperatures [4], and proposed that, in Fe 3 Mo 3 N, long-range magnetic order is suppressed by the geometric frustration inherent to the η-carbide structure in spite of strong magnetic correlation [5].…”

“…Figure 4 shows field dependences of the magnetization M and its field coefficient dM/dH measured for antiferromagnetic Co 6 W 6 C at 4.2 K and up to 54 T. The magnetization of paramagnetic Co 6 Mo 6 C is also included in the figure for comparison. The magnetization of Co 6 Mo 6 C is nearly linear in contrast to the η-6 counterpart, Co 3 Mo 3 C, in which an itinerant electron metamagnetic transition was observed at ∼30 T [6]. Generally, the material which shows a hump in χ(T ) shows an itinerant electron metamagnetism and vice versa [24,25].…”

Itinerant electronic ferromagnetism in Sr2ScO3CoAs with largely spaced CoAs conduction layers

“…Several new topics have recently sprung from this field, e.g., iron-based η-carbide-type compounds with the stella quadrangula network, where itinerant electronic magnetism collaborates with a geometrical frustration, 1,2 and UCoGe in which superconductivity and itinerant electronic ferromagnetism coexist. [3][4][5] Collaboration between low-dimensionality and itinerant electronic magnetism is also one of the interesting topics.…”

Magnetic properties of Fe2GeMo3N; an experimental and computational study

“…Nitrides with the so-called h-carbide structure, 1 for example Fe 3 Mo 3 N and Co 3 Mo 3 N, have been the subject of many recent studies that have addressed either their mechanical properties and hardness, 2,3 their catalytic activity [4][5][6][7][8] or their electrical 9 and magnetic properties. [10][11][12][13] Our interest lies in the latter. Although an earlier study 14 reported that Fe 3 Mo 3 N is antiferromagnetic below 120 K, the most recent neutron diffraction and M€ ossbauer data 11 show convincingly that no long-range magnetic order is present at 4.5 K. The temperature dependence of the electrical resistivity and the specific heat led Waki et al to describe this compound as behaving like a non-Fermi liquid close to a ferromagnetic quantum critical point.…”

“…The isostructural compound Co 3 Mo 3 N has been described as a Pauli paramagnet, with the absence of long-range magnetic order having been proved by nuclear magnetic resonance spectroscopy. 10 A study 15 of the mixed-metal system Fe 3Àx Co x Mo 3 N revealed a large enhancement of the magnetisation of Fe 2.5 Co 0.5 Mo 3 N below 30 K in a field of 100 Oe, but no evidence for long-range magnetic order was apparent in neutron diffraction data collected at 5 K; the compound was described as a superparamagnet. It was also observed that the distribution of iron and cobalt over the two available sites in the structure was not random.…”