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Register a new userStructural, transport, magnetic properties and Raman spectroscopy of orthorhombic Y$1-x$CaxMnO3(0 <= x <= 0.5)
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Orthorhombic Y$_{1-x}$Ca$_x$MnO$_3$ ($0 leq x leq 0.5$) was prepared under high pressure and the variations with $x$ of its structural, magnetic, electrical properties and the polarized Raman spectra were investigated. The lattice parameters change systematically with $x$. Although there are strong indications for increasing disorder above $x = 0.20$, the average structure remains orthorhombic in the whole substitutional range. Ca doping increases conductivity, but temperature dependence of resistivity $rho$(T) remains semiconducting for all $x$. The average magnetic exchange interaction changes from antiferromagnetic for $x < 0.08$ to ferromagnetic for $x > 0.08$. The evolution with $x$ of the Raman spectra provides evidence for increasingly disordered oxygen sublattice at $x geq 0.10$, presumably due to quasistatic and/or dynamical Jahn-Teller distortions.
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We combine the results of magnetic and transport measurements with neutron diffraction data to construct the structural and magnetic phase diagram of the entire family of SrMn$_{1-x}$Ru$_{x}$O$_3$ ($0 leqslant x leqslant 1$) perovskites. We have found antiferromagnetic ordering of the C type for lightly Ru-substituted materials ($0.06 leqslant x leqslant 0.5$) in a similar manner to $R_{y}$Sr$_{1-y}$MnO$_3$ ($R$=La, Pr), due to the generation of Mn$^{3+}$ in both families of manganite perovskites by either $B$-site substitution of Ru$^{5+}$ for Mn$^{4+}$ or $A$-site substitution of $R^{3+}$ for Sr$^{2+}$. This similarity is driven by the same ratio of $d^4$ / $d^3$ ions in both classes of materials for equivalent substitution level. In both cases, a tetragonal lattice distortion is observed, which for some compositions ($0.06 leqslant x leqslant 0.2$) is coupled to a C-type AF transition and results in a first order magnetic and resistive transition. Heavily substituted SrMn$_{1-x}$Ru$_{x}$O$_3$ materials are ferromagnetic due to dominating exchange interactions between the Ru$^{4+}$ ions. Intermediate substitution ($0.6 leqslant x leqslant 0.7$) leads to a spin-glass behavior instead of a quantum critical point reported previously in single crystals, due to enhanced disorder.
We report crystal growth and Raman spectroscopy characterization of pure and mixed bulk topological insulators. The series comprises of both binary and ternary tetradymite topological insulators. We analyzed in detail the Raman peaks of vibrational modes as out of plane Ag, and in plane Eg for both binary and ternary tetradymite topological insulators. Both out of plane Ag exhibit obvious atomic size dependent peak shifts and the effect is much lesser for the former than the latter. The situation is rather interesting for in plane Eg, which not only shows the shift but rather a broader hump like structure. The de convolution of the same show two clear peaks, which are understood in terms of the presence of separate in plane BiSe and BiTe modes in mixed tetradymite topological insulators. Summarily, various Raman modes of well-characterized pure and mixed topological insulator single crystals are reported and discussed in this article.
GdCo$_5$ may be considered as two sublattices - one of Gd and one of Co - whose magnetizations are in antiparallel alignment, forming a ferrimagnet. Substitution of nickel in the cobalt sublattice of GdCo$_5$ has been investigated to gain insight into how the magnetic properties of this prototype rare-earth/transition-metal magnet are affected by changes in the transition metal sublattice. Polycrystalline samples of GdCo$_{5-x}$Ni$_x$ for 0 $ leq x leq $ 5 were synthesized by arc melting. Structural characterization was carried out by powder x-ray diffraction and optical and scanning electron microscope imaging of metallographic slides, the latter revealing a low concentration of Gd$_2$(Co, Ni)$_7$ lamellae for $x leq 2.5$. Compensation - i.e. the cancellation of the opposing Gd and transition metal moments is observed for $1 leq x leq 3$ at a temperature which increases with Ni content; for larger $x$, no compensation is observed below 360 K. A peak in the coercivity is seen at $x approx 1$ at 10K coinciding with a minimum in the saturation magnetization. Density-functional theory calculations within the disordered local moment picture reproduce the dependence of the magnetization on Ni content and temperature. The calculations also show a peak in the magnetocrystalline anisotropy at similar Ni concentrations to the experimentally observed coercivity maximum.
Dirac matters provide a platform for exploring the interplay of their carriers with other quantum phenomena. Sr$_{1-x}$Mn$_{1-y}$Sb$_2$ has been proposed to be a magnetic Weyl semimetal and provides an excellent platform to study the coupling between Weyl fermions and magnons. Here, we report comprehensive inelastic neutron scattering (INS) measurements on single crystals of Sr$_{1-x}$Mn$_{1-y}$Sb$_2$, which have been well characterized by magnetization and magnetotransport measurements, both of which demonstrate that the material is a topologically nontrivial semimetal. The INS spectra clearly show a spin gap of $sim6$ meV. The dispersion in the magnetic Mn layer extends up to about 76 meV, while that between the layers has a narrow band width of 6 meV. We find that the linear spin-wave theory using a Heisenberg spin Hamiltonian can reproduce the experimental spectra with the following parameters: a nearest-neighbor ($SJ_1sim28.0$ meV) and next-nearest-neighbor in-plane exchange interaction ($SJ_2sim9.3$ meV) , interlayer exchange coupling ($SJ_csim-0.1$ meV), and spin anisotropy constant ($SDsim-0.07$ meV). Despite the coexistence of Weyl fermions and magnons, we find no clear evidence that the magnetic dynamics are influenced by the Weyl fermions in Sr$_{1-x}$Mn$_{1-y}$Sb$_2$, possibly because that the Weyl fermions and magnons reside in the Sb and Mn layers separately, and the interlayer coupling is weak due to the quasi-two-dimensional nature of the material, as also evident from the small $SJ_c$ of -0.1 meV.
Here we report the evolution of structural, magnetic and transport properties in MnBi$_{2-x}$Sb$_x$Te$_4$ (0$leq x leq$2) single crystals. MnSb$_2$Te$_4$, isostructural to MnBi$_2$Te$_4$, has the lattice parameters of textit{a}=4.2445(3)$AA$ and textit{c}=40.869(5)$AA$, respectively. With increasing Sb content in MnBi$_{2-x}$Sb$_x$Te$_4$, the textit{a}-lattice decreases linearly following the Vegards law while the textit{c}-lattice shows little compositional dependence. The textit{a}-lattice contraction occurs by reducing Mn-Te-Mn bond angle while Mn-Te bond length remains nearly constant. The anisotropic magnetic properties suggest an antiferromagnetic order below T$_N$=19,K for MnSb$_2$Te$_4$ with the magnetic moments aligned along the crystallographic textit{c}-axis. The antiferromagnetic ordering temperature slightly decreases from 24,K for MnBi$_2$Te$_4$ to 19,K for MnSb$_2$Te$_4$. More dramatic change was observed for the critical magnetic fields required for the spin-flop transition and moment saturation. With increasing Sb content, both critical fields decrease and in MnSb$_2$Te$_4$ a small field of 3,kOe is enough to saturate the moment. In high magnetic fields, the saturation moment shows significant suppression from 3.56$mu_B$/Mn for MnBi$_2$Te$_4$ to 1.57$mu_B$/Mn for MnSb$_2$Te$_4$. Data analyses suggest that both the interlayer magnetic interaction and single ion anisotropy decrease with increasing Sb content. The partial substitution of Bi by Sb also dramatically affects the transport properties. A crossover from n-type to p-type conducting behavior is observed around x=0.63. Our results show close correlation between structural, magnetic and transport properties in MnBi$_{2-x}$Sb$_x$Te$_4$ and that partial substitution of Bi by Sb is an effective approach to fine tuning both the magnetism and transport properties of MnBi$_{2-x}$Sb$_x$Te$_4$.
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