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Register a new userEvolution of structural, magnetic and transport properties in MnBi2-xSbxTe4
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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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We show that type-II Weyl point formation in MnBi2-xSbxTe4 is more likely than in MnBi2Te4 when x reaches 0.5, as the alloy case does not suffer from the same degree of lattice parameter sensitivity as in MnBi2Te4. To further substantiate the stability of type-II Weyl points in MnBi2-xSbxTe4, we demonstrate that among the three conditions of establishing a type-II Weyl point, two are robustly satisfied by the zone-folded dispersion of Bi and Te pz orbitals and spin-orbit coupling already available in MnBi2Te4, and that the control over MnBi2-xSbxTe4 alloy composition provides a rational means to satisfy the third condition. The stability of type-II Weyl points in MnBi1.5Sb0.5Te4 is thus intimately associated with orbital interactions, providing a concrete foundation for future efforts in band engineering and the rational design of topological electronic structures.
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.
Electrical conductivity, thermopower and magnetic properties of Fe-intercalated Fe0.33VSe2 has been reported between 4.2K - 300K. We observe a first order transition in the resistivity of the sintered pellets around 160K on cooling. The electronic properties including the transitional hysteresis in the resistance anomaly (from 80K-160K) are found to be very sensitive to the structural details of the samples, which were prepared in different annealing conditions. The thermopower results on the sintered pellets are reported between 10K - 300K. The magnetic measurements between 2K - 300K and up to 14 Tesla field show the absence of any magnetic ordering in Fe0.33VSe2. The magnetic moment per Fe -atom at room temperature (between 1.4 to 1.7 Bohr Magneton) is much lower than in previously reported anti-ferromagnetic FeV2Se4. Furthermore, the Curie constant shows a rapid and continuous reduction and combined with the high field magnetization result at 2K suggests a rapid decrease in the paramagnetic moments on cooling to low temperatures and the absence of any magnetic order in Fe0.33VSe2 at low temperatures.
Nanostructured La0.67Ca0.33MnO3 (NS-LCMO) was formed by pulsed-laser deposition on the surface of porous Al2O3. The resistance peak temperature (Tp) of the NS-LCMO increases with increasing average thickness of the films, while their Curie temperatures (Tc) remain unchanged. The coercive field of the samples increases with decreasing film thickness and its temperature dependence can be well described by Hc(T) = Hc(0)[1-(T/TB)1/2]. A large magnetoresistance and strong memory effect were observed for the NS-LCMO. The results are discussed in terms of the size effect, Coulomb blockade and magnetic tunneling effect. This work also demonstrates a new way to get nanostructured manganites.
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.
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