Cr-based Compounds Research Articles

Unconventional superconductivity in Cr-based compound Pr3Cr10−xN11

We report results of specific heat and muon spin relaxation (μSR) measurements on a polycrystalline sample of Pr3Cr10−xN11, which shows superconducting state below Tc = 5.25 K, a large upper critical field Hc2 ~ 20 T and a residual Sommerfeld coefficient γ0. The field dependence of γ0(H) resembles γ of the U-based superconductors UTe2 and URhGe at low temperatures. The temperature-dependent superfluid density measured by transverse-field μSR experiments is consistent with a p-wave pairing symmetry. ZF-μSR experiment suggests a time-reversal symmetry broken superconducting transition, and temperature-independent spin fluctuations at low temperatures are revealed by LF-μSR experiments. These results indicate that Pr3Cr10−xN11 is a candidate of p-wave superconductor which breaks time-reversal symmetry.

ThCr2Si2C: An Antiferromagnetic Metal with a Cr2C Square Lattice.

A quaternary compound, ThCr2Si2C, was synthesized by using the arc-melting technique. The compound adopts a tetragonal CeCr2Si2C-type crystal structure. The electronic resistivity and specific heat data exhibit metallic behavior, while the magnetic susceptibility displays a pronounced broad peak at around 370 K, indicating the antiferromagnetic phase transition. The first-principles calculations suggest A-type antiferromagnetic ordering of the Cr sublattice, which is confirmed by neutron diffraction experiments. By comparing the crystal structure of ThCr2Si2C with the isostructural Cr-based compounds, the magnetic state of Cr 3d orbital is discussed in terms of the band-filling effects and indirect spin exchange interaction.

Microstructural development and aging behavior of Al–Cr–Zr heat-resistant alloy fabricated using laser powder bed fusion

Using laser powder bed fusion (L-PBF), we designed and fabricated specimens of a heat-resistant Al–4mass%Cr–1.5mass%Zr alloy (Al–4Cr–1.5Zr). The Al–4Cr–1.5Zr L-PBF specimen achieved high relative density greater than 99.9% by optimizing the laser scan conditions. The hardness and tensile and 0.2% proof stresses of the Al–4Cr–1.5Zr L-PBF specimens significantly increased after aging heat treatments, and the peak-aged specimens exhibited excellent high-temperature strength. The L-PBF specimens consisted of coarse columnar and fine equiaxed crystal grains owing to heterogeneous nucleation by the primarily crystallized Al3Zr phase. In the peak-aged L-PBF specimen, a finely dispersed Al3Zr granular phase on the order of single nanometers was precipitated in the α-Al matrix by aging. Meanwhile, the chromium was supersaturated in an α-Al solid solution even after peak aging, and partially precipitated into coarse granular Al–Cr-based compounds. These multi-scale microstructural observation results revealed that the dominant strengthening factors in the Al–4Cr–1.5Zr L-PBF specimens were precipitation hardening by the fine L12-Al3Zr phase having a strong crystallographic consistency with the α-Al matrix, solid-solution hardening with chromium, dispersion hardening due to the Al–Cr-based compounds, and hardening by the crystal grain refinement mainly with the fine equiaxed grains.

Multiple field-induced phases in the frustrated triangular magnet Cs3Fe2Br9

The recently discovered material Cs$_3$Fe$_2$Br$_9$ contains Fe$_2$Br$_9$ bi-octahedra forming triangular layers with hexagonal stacking along the $c$ axis. In contrast to isostructural Cr-based compounds, the zero-field ground state is not a nonmagnetic $S=0$ singlet-dimer state. Instead, the Fe$_2$Br$_9$ bi-octahedra host semiclassical $S=5/2$ Fe$^{3+}$ spins with a pronounced easy-axis anisotropy along $c$ and interestingly, the intra-dimer spins are ordered ferromagnetically. The high degree of magnetic frustration due to (various) competing intra- and inter-dimer couplings leads to a surprisingly rich magnetic phase diagram. Already the zero-field ground state is reached via an intermediate phase, and the high-field magnetization and thermal expansion data for $H\parallel c$ identify ten different ordered phases. Among them are phases with constant magnetization of 1/3, respectively 1/2 of the saturation value, and several transitions are strongly hysteretic with pronounced length changes reflecting strong magnetoelastic coupling.

The chromium pnictide materials: A tunable platform for exploring new exciting phenomena

Among intermetallic compounds between 3d transition metals and pnictogens, compounds containing chromium and arsenide ions are of special interest due to their rich variety of electronic, magnetic and superconducting properties. The monopnictide CrAs compound, although known since over fifty years ago, was observed to exhibit pressure-induced superconductivity in the vicinity of an antiferromagnetic quantum critical point, making it the first superconductor among Cr-based compounds. After this discovery, seeking for ambient pressure superconductivity in Cr-based compounds, bulk superconductivity was discovered in the pnictide K2Cr3As3. These discoveries boost the search and the investigation of the several interesting phenomena exhibited by these materials that actually need to be properly addressed. Here, we try to give a comprehensive overview on these materials showing that they may provide a tunable platform for emphasising the role played by the quantum criticality, the low dimensionality, the magnetic fluctuations and the topology.

Superconductivity induced by aging and annealing in K1−δCr3As3Hx

There has been a puzzling discrepancy on the physical property of quasi-one-dimensional Cr-based compound ${\mathrm{KCr}}_{3}{\mathrm{As}}_{3}$. While the polycrystalline ${\mathrm{KCr}}_{3}{\mathrm{As}}_{3}$ was originally reported to be nonsuperconducting with a spin-glass ground state, the single-crystalline ${\mathrm{KCr}}_{3}{\mathrm{As}}_{3}$ was later found to exhibit superconductivity at $\ensuremath{\sim}5$ K. Here we demonstrate that both the polycrystals and single crystals can be made either nonsuperconducting or superconducting. The pristine samples show a spin-glass behavior only, and superconductivity below 5 K is actually induced by the post-aging and/or post-annealing. The result can be understood in terms of hydrogen intercalation into the one-dimensional ${\mathrm{Cr}}_{3}{\mathrm{As}}_{3}$ tubes, which was discovered very recently by K. M. Taddei et al. (arXiv:1905.03360). In addition, significant K deficiency and microscopic inhomogeneity have been revealed, suggesting a phase separation scenario with columnar superconductivity in ${\mathrm{K}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{Cr}}_{3}{\mathrm{As}}_{3}{\mathrm{H}}_{x}$. The possible processes of the hydrogen intercalation are given.

Superconductivity in chromium nitrides Pr3Cr10-xN11 with strong electron correlations.

Exploration of superconductivity in Cr-based compounds has attracted considerable interest because only a few Cr-based superconductors (CrAs, A2Cr3As3 and ACr3As3 (A = K, Rb, Cs, Na)) have been discovered so far and they show an unconventional pairing mechanism. We report the discovery of bulk superconductivity at 5.25 K in chromium nitride in Pr3Cr10-xN11 with a cubic lattice structure. A relatively large upper critical field of Hc2(0) ∼ 12.6 T is determined, which is larger than the estimated Pauli-paramagnetic pair-breaking magnetic field. The material has a large electronic specific-heat coefficient of 170 mJ K−2 mol−1—about 10 times larger than that estimated by the electronic structure calculation, which suggests that correlations between 3d electrons are very strong in Pr3Cr10-xN11, and thus quantum fluctuations might be involved. Electronic structure calculations show that the density of states at the Fermi energy are contributed predominantly by Cr 3d electrons, implying that the superconductivity results mainly from the condensation of Cr 3d electrons. Pr3Cr10-xN11 represents a rare example of possible unconventional superconductivity emerging in a 3D system with strong electron correlations. Nevertheless, clarification of the specific pairing symmetry needs more investigation.

Synthesis and crystal structure of La21Cr8-2a Al b Ge7-b C12 [a = 0.22 (2) and b = 0.758 (19)

Single crystals of a new multinary chromium carbide, La21Cr8-2a Al b Ge7-b C12 (henicosa-lanthanum octa-chromium aluminium hexa-germanium dodeca-carbide), were grown from an La-rich self flux and were characterized by single-crystal X-ray diffraction. The face-centered cubic crystal structure is composed of isolated and geometrically frustrated regular Cr tetra-hedra that are co-centered within regular C octa-hedra. These mutually separated Cr4-aC6 clusters are distributed throughout a three-dimensional framework of Al, Ge, and La. The title compound is isotypic with La21-δMn8X7C12 and R21Fe8X7C12 (R = La, Ce, Pr; X = Al, Bi, Ge, Sn, Sb, Te) and represents the first example of a Cr-based compound with this structure-type.

Nano-plasmonic-based structures for DNA sequencing.

We propose novel nano-plasmonic-based structures for rapid sequencing of DNA molecules. The optical properties of DNA nucleotides have notable differences in the ultraviolet (UV) region of light. Using nanopore, bowtie, and bowtie-nanopore compound structures, probable application of the surface plasmon resonance (SPR) in DNA sequencing is investigated by employing the discrete dipole approximation method. The effects of different materials like chromium (Cr), aluminum (Al), rhodium (Rh), and graphene (Gr) are studied. We show that for Cr/Al/Gr/Rh, the nucleotide presented shifts the SPR spectra for the nanopore 1/29/5/34 to 14/39/15/67 nm, bowtie 8/2/49/38 to 31/20/79/55 nm, and bowtie-nanopore compound 25/77/5/16 to 80/80/22/39 nm. The Cr-based compound structure shows excellent sensitivity and selectivity which can make it a promising methodology for DNA sequencing.

Computational discovery of stableM2AXphases

The family of layered ${M}_{n+1}A{X}_{n}$ compounds provides a large class of materials with applications ranging from magnets to high-temperature coatings to nuclear cladding. In this work, we employ a density-functional-theory-based discovery approach to identify a large number of thermodynamically stable ${M}_{n+1}A{X}_{n}$ compounds, where $n=1$, $M=\text{Sc}$, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; $A=\text{Al}$, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, Pb; and $X=\text{C}$, N. We calculate the formation energy for 216 pure ${M}_{2}AX$ compounds and 10 314 solid solutions, ${(M{M}^{\ensuremath{'}})}_{2}(A{A}^{\ensuremath{'}})(X{X}^{\ensuremath{'}})$, relative to their competing phases. We find that the 49 experimentally known ${M}_{2}AX$ phases exhibit formation energies of less than 30 meV/atom. Among the 10 530 compositions considered, 3140 exhibit formation energies below 30 meV/atom, most of which have yet to be experimentally synthesized. A significant subset of 301 compositions exhibits strong exothermic stability in excess of 100 meV/atom, indicating favorable synthesis conditions. We identify empirical design rules for stable ${M}_{2}AX$ compounds. Among the metastable ${M}_{2}AX$ compounds are two Cr-based compounds with ferromagnetic ordering and expected Curie temperatures around 75 K. These results can serve as a map for the experimental design and synthesis of different ${M}_{2}AX$ compounds.

The discovery of superconductivity in Cr-based compounds

The discovery of superconductivity in Cr-based compounds

Cluster spin-glass ground state in quasi-one-dimensionalKCr3As3

We report structural and physical properties of a new quasi-one-dimensional Cr-based compound, KCr$_{3}$As$_{3}$, which is prepared by potassium deintercalation from the superconductive K$_{2}$Cr$_{3}$As$_{3}$. KCr$_{3}$As$_{3}$ adopts the TlFe$_{3}$Te$_{3}$-type structure with space group $P6_{3}$/$m$ (No. 176). The high-temperature magnetic susceptibility obeys the Curie-Weiss law with an effective magnetic moment of 0.68 $\mu_{\mathrm{B}}$/Cr. Below 56 K the susceptibility deviates from the high-temperature Curie-Weiss behavior, coinciding with the rapid increase in resistivity, which suggests formation of spin clusters. The short-range spin correlations are also supported by the specific-heat data. The title material does not exhibit bulk superconductivity; instead, it shows a cluster spin-glass state below $\sim$ 5 K.

Magnetic Properties of Cr-based Ternary Compound CrAlGe

Structural and magnetic properties of Cr-based compound CrAlGe were investigated. The crystal structure was found to be an orthorhombic TiSi2-type with lattice parameters a = 0.4770nm, b = 0.8254nm and c = 0.8725nm at room temperature. Magnetization curve of CrAlGe showed the ferromagnetic behavior. The saturation magnetic moment, spontaneous magnetic moment and Curie temperature of CrAlGe were determined to be 0.45μB/f.u., 0.41μB/f.u. and TC = 80K, respectively. For the temperature T below 30K, the decrease in the square of the spontaneous magnetization M0(T)2 was proportional to T2. However, for 30 <T <TC, the decrease in M0(T)2 was proportional to T4/3. Obtained results suggest that CrAlGe is a weak itinerant electron ferromagnet.

Perpendicular Magnetic Anisotropy in FePt Patterned Media Employing a CrV Seed Layer.

A thin FePt film was deposited onto a CrV seed layer at 400°C and showed a high coercivity (~3,400 Oe) and high magnetization (900–1,000 emu/cm3) characteristic of L10 phase. However, the magnetic properties of patterned media fabricated from the film stack were degraded due to the Ar-ion bombardment. We employed a deposition-last process, in which FePt film deposited at room temperature underwent lift-off and post-annealing processes, to avoid the exposure of FePt to Ar plasma. A patterned medium with 100-nm nano-columns showed an out-of-plane coercivity fivefold larger than its in-plane counterpart and a remanent magnetization comparable to saturation magnetization in the out-of-plane direction, indicating a high perpendicular anisotropy. These results demonstrate the high perpendicular anisotropy in FePt patterned media using a Cr-based compound seed layer for the first time and suggest that ultra-high-density magnetic recording media can be achieved using this optimized top-down approach.

An in-Situ Chloride-Generated Route to Various One-Dimensional Nanostructures of Chromium-Based Compounds

A convenient in-situ chloride-generated route has been developed to fabricate various novel one-dimensional nanostructures of Cr-based compounds including CrSi2, CrN and SiNx-coated CrSi2, CrN (with a trace of CrSi2), and CrN−CrSi2 intermediate composites for the first time. And the evolution of the products has been clearly illuminated on the basis of involved chemistry and the convincing characterization results. The diverse regulation of the products, the simplicity of the preparation procedure, and the wide potential applications of this route make this study both scientifically and technologically interesting.

Role of the presence of transition-metal atoms at the antisites in CrAs, CrSe and VAs zinc-blende compounds

In a recent publication [I. Galanakis, K. Özdog˜an, E. Şaşıog˜lu, B. Aktaş, Phys. Rev. B 74 (2006) 140408(R)] we have shown that in the case of CrAs and related transition-metal chalcogenides and pnictides, crystallizing in the zinc-blende structure, the excess of the transition-metal atoms leads to half-metallic ferrimagnetism. The latter property is crucial for spintronic applications with respect to ferromagnets due to the lower stray fields created by these materials. We extend this study to cover the case where the transition-metal atoms sitting at antisites are not identical to the ones in the perfect sites. In Cr-based compounds, the creation of Mn antisites keeps the half-metallic ferrimagnetic character produced also by the Cr antisites. In the case of VAs, Cr and Mn antisites keep the half-metallic character of VAs (contrary to V antisites) due to the larger exchange splitting exhibited by these atoms.