Spin Dynamics and Unconventional Magnetism in Insulating La(1–2x)Sr2xCo(1–x)NbxO3
19 Aug 2019-Journal of Physical Chemistry C (American Chemical Society)-Vol. 123, Iss: 36, pp 22457-22469
TL;DR: In this paper, the structural, magnetic, transport, and electronic properties of LaCoO3 with Sr/Nb cosubstitution were studied using X-ray and neutron diffraction, dc-and ac-magnetiza...
Abstract: We study the structural, magnetic, transport, and electronic properties of LaCoO3 with Sr/Nb cosubstitution, i.e., La(1–2x)Sr2xCo(1–x)NbxO3 using X-ray and neutron diffraction, dc- and ac-magnetiza...
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01 Jan 2010
TL;DR: In this paper, the authors focus on Mott insulator, and a simple theoritical way to describe this metal insulator transition (MIT) is the Hubbard Model, which is characterized by the conductivity which will be zero in the insulator phase.
Abstract: Metal Insulator transition(MIT) is characterized by the conductivity which will be zero in the insulator phase. In this term paper, we focus on Mott insulator, and a simple theoritical way to describe this MIT is the Hubbard Model .Finally, we will look at the experiments of Mott insulator transition .
166 citations
TL;DR: In this article, the structural, magnetic, and spin-state transitions, and magnetocaloric properties of double perovskites were investigated, and the correlation between complex magnetic interactions and the presence of various Co spin states in the system was discussed.
Abstract: We investigate the structural, magnetic, and spin-state transitions, and magnetocaloric properties of ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{CoNbO}}_{6}$ ($x=0$--1) double perovskites. The structural transition from tetragonal to monoclinic phase at $x\ensuremath{\geqslant}0.6$, and an evolution of (101)/(103) superlattice reflections and Raman active modes indicate the enhancement in the B-site ordering with $x$. The magnetic susceptibility data reveal the transition from weak ferromagnetic (FM) to antiferromagnetic (AFM) ordering for $x\ensuremath{\geqslant}0.6$ with ${T}_{\mathrm{N}}\ensuremath{\approx}9$--15 K. Interestingly, the La substitution drives towards a more insulating state due to an increase in high-spin ${\mathrm{Co}}^{2+}$, whereas a spin-state crossover is observed in ${\mathrm{Co}}^{3+}$ from high-spin to intermediate-/low-spin states with $x$. We discuss the correlation between complex magnetic interactions and the presence of various Co spin states in the system. Moreover, the emergence of metamagnetic nature due to the competition between FM and AFM interactions as well as crossover from conventional to inverse magnetocaloric effect have been demonstrated by a detailed analysis of temperature and field dependent change in magnetic entropy.
21 citations
TL;DR: In this paper, the magnetic and structural properties of bulk and nanoparticle powders of LaCoO3 (LCO) were studied using SQUID magnetometry and neutron diffraction, and a core-interface model was introduced, with the core region exhibiting the strong to weak antiferromagnetic crossover and with FM in the interface region near surfaces and impurity phases.
Abstract: Bulk and nanoparticle powders of LaCoO3 (LCO) were synthesized, and their magnetic and structural properties were studied using SQUID magnetometry and neutron diffraction. The bulk and large nanoparticles exhibit weak ferromagnetism (FM) below T ~ 85K and a crossover from strong to weak antiferromagnetic (AFM) correlations near a transition expressed in the lattice parameters, To ~ 40K. This crossover does not occur in the smallest nanoparticles; instead, the magnetic behavior is predominantly ferromagnetic. The amount of FM in the nanoparticles depends on the amount of Co3O4 impurity phase, which induces tensile strain on the LCO lattice. A core-interface model is introduced, with the core region exhibiting the AFM crossover and with FM in the interface region near surfaces and impurity phases.
14 citations
TL;DR: In this article, X-ray absorption spectroscopy was used to investigate the local structure and electronic properties of bulk La1−ySryCo1−xNbxO3 (y = 2x as LSCNO and y = 0 as LCNO) samples.
Abstract: We use X-ray absorption spectroscopy to investigate the local structure and electronic properties of bulk La1–ySryCo1–xNbxO3 (y = 2x as LSCNO and y = 0 as LCNO) samples. The X-ray absorption near-e...
12 citations
TL;DR: In this article, the specific heat and ac susceptibility for magnetically frustrated double perovskites were analyzed for low-temperature complex magnetic interactions and their evolution with magnetic field.
Abstract: We report the detailed analysis of specific heat $[{C}_{P}(T)]$ and ac susceptibility for magnetically frustrated ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{CoNbO}}_{6}$ $(x=0--1)$ double perovskites to understand low-temperature complex magnetic interactions and their evolution with $x$. Interestingly, the observed Schottky anomaly in the $x\ensuremath{\leqslant}0.4$ samples shifts gradually toward higher temperatures with magnetic field as well as $x$, and the analysis reveals the persistence of the discrete energy states in these samples resulting from the spin-orbit coupling and octahedral distortion. Moreover, the extracted values of the Land\'e $g$ factor indicate the existence of high-spin state ${\mathrm{Co}}^{3+}$ ions energetically close to a nonmagnetic low-spin state. The specific-heat data show the $\ensuremath{\lambda}$-type anomaly for the $x\ensuremath{\geqslant}0.6$ samples due to evolution of the long-range antiferromagnetic ordering. Our analysis of low-temperature ${C}_{P}(T)$ data for the $x\ensuremath{\geqslant}0.6$ samples demonstrates the 3D isotropic Heisenberg antiferromagnetic (AFM) interactions and the temperature-induced second-order AFM-paramagnetic phase transition. More interestingly, we demonstrate the presence of the free ${\mathrm{Co}}^{2+}$-like Kramers doublet ground state in the $x=1$ sample. Further, the ac susceptibility and time evolution of the magnetization data reveal the low-temperature cluster-glass-like behavior in the $x=0--0.4$ samples, where spin-spin correlation strength decreases with $x$.
12 citations
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
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TL;DR: In this paper, it was shown that both electrical conduction and ferromagnetic coupling in these compounds arise from a double exchange process, and a quantitative relation was developed between electrical conductivity and the Ferromagnetic Curie temperature.
Abstract: Recently, Jonker and Van Santen have found an empirical correlation between electrical conduction and ferromagnetism in certain compounds of manganese with perovskite structure. This observed correlation is herein interpreted in terms of those principles governing the interaction of the $d$-shells of the transition metals which were enunciated in the first paper of this series. Both electrical conduction and ferromagnetic coupling in these compounds are found to arise from a double exchange process, and a quantitative relation is developed between electrical conductivity and the ferromagnetic Curie temperature.
5,097 citations
TL;DR: In this paper, it is shown that the spin coupling between the incomplete $d$ shells and the conduction electrons leads to a tendency for a ferromagnetic alignment of $d $ spins.
Abstract: It is assumed (1) that the interaction between the incomplete $d$ shells of the transition elements is insufficient to disrupt the coupling between the $d$ electrons in the same shells, and (2) that the exchange interaction between adjacent $d$ shells always has the same sign irrespective of distance of separation. The direct interaction between adjacent $d$ shells then invariably leads to a tendency for an antiferromagnetic alignment of $d$ spins. The body-centered cubic structure of the transition metals V, Cr, Cb, Mo, Ta, and W is thereby interpreted, as well as more complex lattices of certain alloys. It is demonstrated that the spin coupling between the incomplete $d$ shells and the conduction electrons leads to a tendency for a ferromagnetic alignment of $d$ spins. The occurrence of ferromagnetism is thereby interpreted in a much more straightforward manner than through the ad hoc assumption of a reversal in sign of the exchange integral. The occurrence of antiferromagnetism and of ferromagnetism in various systems is readily understood, and certain simple rules are deduced for deciding which type of magnetism will occur in particular alloys.
1,660 citations