Magnetic and Structural Studies of G-Phase Compound Mn6Ni16Si7 (original) (raw)
Related papers
On the crystal structure of the Mn–Ni–Si G-phase
Journal of Alloys and Compounds, 2009
The crystal structure of Mn 6 Ni 16 Si 7 was reinvestigated by X-ray powder, single crystal and neutron powder diffraction data in form of a combined refinement. In contrast to the various structure variants observed for titanium aluminium-based G-phases Ti 6 ({Fe,Co,Ni} 1−x Al x) 23+1 as well as for Ti 6 Ni 16+x Si 7 , Mn 6 Ni 16 Si 7 was confirmed to crystallize as a simple ordered variant of the Th 6 Mn 23 structure type (a = 1.11674(6) nm, Mg 6 Cu 16 Si 7type; space group Fm3m): Ni atoms adopt two 32f sites, Si atoms occupy 4a and 24d sites and Mn-atoms are located at 24e sites. A Fourier difference map proved the absence of atoms in the 4b site (1/2, 1/2, 1/2). Thus the crystal structure of Mn 6 Ni 16 Si 7 is a true representative of the Mg 6 Cu 16 Si 7-type.
Absence of first order magnetic transition, a curious case of Mn 3 InC
Journal of Applied Physics
The volume expanding magnetostructural transition in Mn 3 GaC and Mn 3 SnC has been identified to be due to distortion of Mn 6 C octahedra. Despite a similar lattice volume as Mn 3 SnC and similar valence electron contribution to density of states as in Mn 3 GaC, Mn 3 InC does not undergo a first order magnetostructural transformation like the Ga and Sn antiperovskite counterparts. A systematic investigation of its structure and magnetic properties using probes like x-ray diffraction, magnetization measurements, neutron diffraction and extended x-ray absorption fine structure (EXAFS) reveal that though the octahedra are distorted resulting in long and short Mn-Mn bonds and different magnetic moments on Mn atoms, the interaction between them remains ferromagnetic. This has been attributed to the strain on the Mn 6 C octahedra produced due to relatively larger size of In atom compared to Sn and Ga. The size of In atom constricts the deformation of Mn 6 C octahedra giving rise to Mn-Mn distances that favor only ferromagnetic interactions in the compound.
The structures and magnetic properties of Mn clusters containing 13, 15, 19, and 23 atoms have been predicted from ab initio electronic structure calculations. The lowest energy structures of the 13-, 19-, and 23-atom clusters are icosahedral and have ordered spin configurations in which blocks of ferromagnetically coupled spins are antiferromagnetically coupled with each other. The 15-atom cluster is body-centered cubic with antiferromagnetic coupling. The net moments are small and lie in the range of 0.2-1.2 B /atom; however, the average local atomic moments have high values close to 4 B . These results are discussed in light of recent Stern-Gerlach experiments.
Dalton Transactions, 2009
ethylenediamine (H 4 edte) with MnCl 2 ·4H 2 O or FeCl 3 ·6H 2 O in MeOH or MeCN with different bases yield four butterfly-like tetranuclear clusters with fused defective dicubane M 4 O 6 cores: [Mn II 2 Mn IV 2 (m 4 -Hedte) 2 (thme) 2 ]·MeCN (1) (H 4 edte = N,N,N¢,N¢-tetrakis(2-hydroxyethyl)ethylenediamine, H 3 thme = 1,1,1-tris(hydroxymethyl)ethane), [Mn II 2 Mn IV 2 (m 4 -Hedte) 2 (thme) 2 ]·2MeOH (2), [Fe III 4 (m 4 -Hedte) 2 (N 3 ) 6 ]·2MeCN and [Fe III 4 (m 4 -edte) 2 -(N 3 ) 4 (MeOH) 2 ] (4). Both 1 and 3 crystallize in the triclinic space group P1, while 2 and 4 crystallize in the monoclinic space group P2 1 /c and P2 1 /n, respectively. The hexadentate Hedte 3ligand in 1-3, and the edte 4ligand in 4 acts in a similar m 4 :h 1 :h 1 :h 1 :h 2 :h 2 :h 3 coordination mode to bridge four metal ions into butterfly-like tetranuclear clusters with fused defective dicubane M 4 O 6 cores. Magnetic studies show that 2 has the spin ground state S T = 8 while 4 has the spin ground state S T = 0. Within the Mn 4 O 6 cluster core of 2, both Mn(IV) ◊ ◊ ◊ Mn(II) and Mn(II) ◊ ◊ ◊ Mn(II) ferromagnetic interactions (J Mn(IV) ◊ ◊ ◊ Mn(II) = +2.91 cm -1 and J Mn(II) ◊ ◊ ◊ Mn(II) = +7.94 cm -1 ) occur contrary to the Fe 4 O 6 core, where antiferromagnetic exchange exists (J aptical-Fe(III) ◊ ◊ ◊ central-Fe(III) = -15.4 cm -1 and J central-Fe(III) ◊ ◊ ◊ central-Fe(III) = -4.5 cm -1 ).
Journal of Solid State Chemistry, 2004
The crystal structure of the quasi-one-dimensional oxide PbNi 1.88 Mg 0.12 V 2 O 8 has been studied by Rietveld analysis of combined high-resolution neutron and X-ray powder diffraction data at 300 K and at low temperatures. The (Ni/Mg)O 6 octahedral units share a common edge and form spiral chains along the c-axis of the tetragonal unit cell, without deviating the I4 1 cd (Z ¼ 8) symmetry upon cooling. DC magnetic susceptibility measurements show that the system undergoes a magnetic phase transition below T N D3:4 K. Rietveld analysis of the medium resolution neutron powder diffraction data confirms that impurity-induced antiferromagnetic order (with propagation vector, j ¼ ½000) takes over from the Haldane ground state of the parent compound. The power-law [b ¼ 0:31ð3Þ] temperature evolution of the strongest magnetic Bragg peak intensity indicates three-dimensional Ising-type magnetic interactions, while the reduced magnitude of the Ni 2+ moment [/mS ¼ 0:98ð3Þ m B ] suggests important zeropoint spin fluctuations. Structural considerations are consistent with small changes in the interatomic distances around the bridging tetrahedral VO 4 entities separating the chains. However, no bulk structural phase transition concurrent to the Ne´el ordering is found. We show that the modification of intra-and inter-chain Ni-Ni distances upon cooling promotes the magnetic coupling of the end-of-chain liberated S ¼ 1=2 spins and leads to antiferromagnetic ordering. r 2004 Elsevier Inc. All rights reserved. PACS: 61.10.Nz; 61.12.Ld; 75.; 75.30.Hx
Journal of Magnetism and Magnetic Materials
The antiferromagnet Mn 5 Si 3 has recently attracted attention because a noncollinear spin arrangement has been shown to produce a topological anomalous Hall effect and an inverse magnetocaloric effect. Here we synthesize single crystals of Mn 5 Si 3 using flux growth. We determine the phase diagram through magnetization and measure the magnetoresistance and the Hall effect. We find the collinear and noncollinear antiferromagnetic phases at low temperatures and, in addition, a third magnetic phase, in between the two antiferromagnetic phases which has ferromagnetic character. The latter magnetic phase might be caused by strain produced by Cu inclusions that lead to quenched fluctuations of the mixed character magnetic ordering in this compound.
Physical Review B, 2011
The tetragonal σ phase and the hexagonal (hex) phase in the Mn-Si-V(Cr) transition-metal-alloy systems are stable approximant phases of a dodecagonal (12-fold) quasicrystal that can be prepared in bulk quantities. We have synthesized samples of the σ and hex phases of composition Mn 76 Si 18 Cr 6 and determined their magnetic properties. In the σ -Mn 76 Si 18 Cr 6 , a spin-freezing transition to a canonical spin-glass phase was detected below T f ≈ 8 K, characterized by a maximum in the zero-field-cooled susceptibility, a frequency-dependent cusp in the ac susceptibility, M(H ) hysteresis, and ultraslow time decay of the thermoremanent magnetization. In contrast, no spin-glass transition was observed in the hex-Mn 76 Si 18 Cr 6 phase down to the lowest investigated temperature of 2 K. The analysis of the susceptibility has shown that the coupling of spins in both phases is antiferromagnetic (AFM), but the coupling strength is considerably stronger in the σ phase. Since both phases are structurally described by the triangle-square tiling scheme related to that of the dodecagonal quasicrystal, which imposes geometric frustration of the AFM-coupled spins on triangles, the absence of spin-glass transition in the hex-Mn 76 Si 18 Cr 6 could be due to shifting of this transition below the lowest temperature of our experimental setup, as a consequence of weaker spin coupling and smaller moment sizes in the hex phase. In both investigated samples, tiny Mn 3 O 4 inclusions that undergo a transition to a ferrimagnetic phase at T C ≈ 42 K were detected in the magnetic signal. Geometric frustration of interactions between the AFM-coupled spins placed at the vertices of the triangle-square tiling should be a general feature of dodecagonal quasicrystals and their approximants, so that spin-glass-type ordering is expected to occur quite commonly in the dodecagonal phases.
Phase separation and effect of strain on magnetic properties of Mn 3Ga 1 − xSn xC
Journal of Applied Physics, 2018
While the unit cell volume of compounds belonging to the Mn 3 Ga 1−x Sn x C, (0 ≤ x ≤ 1) series shows a conformity with Vegard's law, their magnetic and magnetocaloric properties behave differently from those of parent compounds Mn 3 GaC and Mn 3 SnC. A correlation between the observed magnetic properties and underlying magnetic and local structure suggests that replacing Ga atoms by larger atoms of Sn results in the formation of Ga-rich and Sn-rich clusters. As a result, even though the long range structure appears to be cubic, Mn atoms find themselves in two different local environments. The packing of these two different local structures into a single global structure induces tensile/compressive strains on the Mn 6 C functional unit and is responsible for the observed magnetic properties across the entire solid solution range.