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Register a new userInhomogeneous magnetism in the doped kagome lattice of LaCuO2.66
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The hole-doped kagome lattice of Cu2+ ions in LaCuO2.66 was investigated by nuclear quadrupole resonance (NQR), electron spin resonance (ESR), electrical resistivity, bulk magnetization and specific heat measurements. For temperatures above ~180 K, the spin and charge properties show an activated behavior suggestive of a narrow-gap semiconductor. At lower temperatures, the results indicate an insulating ground state which may or may not be charge ordered. While the frustrated spins in remaining patches of the original kagome lattice might not be directly detected here, the observation of coexisting non-magnetic sites, free spins and frozen moments reveals an intrinsically inhomogeneous magnetism. Numerical simulations of a 1/3-diluted kagome lattice rationalize this magnetic state in terms of a heterogeneous distribution of cluster sizes and morphologies near the site-percolation threshold.
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The layered compound with distorted Kagome nets, Dy3Ru4Al12, was previously reported to undergo antiferromagnetic ordering below (TN=) 7 K, based on investigations on single crystals. Here, we report the results of our investigation of ac and dc magnetic susceptibility (c{hi}), isothermal remnant magnetization (MIRM), heat-capacity, magnetocaloric effect and magnetoresistance measurements on polycrystals. The present results reveal that there is an additional magnetic anomaly around 20 K, as though the Neel order is preceded by the formation of ferromagnetic clusters. We attribute this feature to geometric frustration of magnetism. In view of the existence of this phase, the interpretation of the linear-term in the heat-capacity in terms of spin-fluctuations from the Ru 4d band needs to be revisited. Additionally, in the vicinity of TN, AC c{hi} shows a prominent frequency dependence and, below TN, MIRM exhibits a slow decay with time. This raises a question whether the antiferromagnetic structure in this compound is characterized by spin-glass-like dynamics. In contrast to what was reported earlier, there is a change in the sign of the magnetoresistance (MR) at the metamagnetic transition. A butter-fly-shaped (isothermal) MR loop (interestingly spanning over all the four quadrants) is observed at 2 K with distinct evidence for the magnetic phase co-existence phenomenon in zero field after travelling through metamagnetic transition field. The results on polycrystals thus provide additional information about the magnetism of this compound, revealing that the magnetism of this compound is more complex than what is believed, due to geometric frustration intrinsic to Kagome net.
Strong spin-lattice coupling and prominent frustration effects observed in the 50$%$ Fe-doped frustrated hexagonal ($h$)LuMnO$_3$ are reported. A N{e}el transition at $T_{mathrm N} approx$ 112~K and a possible spin re-orientation transition at $T_{mathrm {SR}} approx$ 55~K are observed in the magnetization data. From neutron powder diffraction data, the nuclear structure at and below 300~K was refined in polar $P6_3cm$ space group. While the magnetic structure of LuMnO$_3$ belongs to the $Gamma_4$ ($P6_3cm$) representation, that of LuFe$_{0.5}$Mn$_{0.5}$O$_3$ belongs to $Gamma_1$ ($P6_3cm$) which is supported by the strong intensity for the $mathbf{(100)}$ reflection and also judging by the presence of spin-lattice coupling. The refined atomic positions for Lu and Mn/Fe indicate significant atomic displacements at $T_{mathrm N}$ and $T_{mathrm {SR}}$ which confirms strong spin-lattice coupling. Our results complement the discovery of room temperature multiferroicity in thin films of $h$LuFeO$_3$ and would give impetus to study LuFe$_{1-x}$Mn$_x$O$_3$ systems as potential multiferroics where electric polarization is linked to giant atomic displacements.
Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several kagome magnets have appeared as the most promising platforms. Here, we explore magnetic correlations in the transition-metal-based kagome magnet TbMn$_{6}$Sn$_{6}$. Our results show that the system exhibits an out-of-plane ferrimagnetic structure $P6/mmm$ (comprised by Tb and Mn moments) with slow magnetic fluctuations in a wide temperature range. These fluctuations exhibit a slowing down below $T_{rm C1}^{*}$ ${simeq}$ 120 K and a slightly modified quasi-static magnetic state is established below $T_{rm C1}$ ${simeq}$ 20 K. A canted variation of the $P6/mmm$ structure is possible, where all moments contribute to a net $c$-axis ferrimagnetic state which exhibits zero net in-plane components. Alternatively, a small incommensurate $k$-vector could arise below $T_{rm C1}$. We further show that the temperature evolution of the anomalous Hall conductivity (AHC) is strongly influenced by the low temperature magnetic crossover. More importantly, the here identified magnetic state seems to be responsible for the large quasi-linear magnetoresistance as well as for the appearance of quantum oscillations, which are related to the quantized Landau fan structure featuring a spin-polarized Dirac dispersion with a large Chern gap. Therefore the exciting perspective of a magnetic system arises in which the topological response can be controlled, and thus explored, over a wide range of parameters.
We present numerical evidence for the crystallization of magnons below the saturation field at non-zero temperatures for the highly frustrated spin-half kagome Heisenberg antiferromagnet. This phenomenon can be traced back to the existence of independent localized magnons or equivalently flat-band multi-magnon states. We present a loop-gas description of these localized magnons and a phase diagram of this transition, thus providing information for which magnetic fields and temperatures magnon crystallization can be observed experimentally. The emergence of a finite-temperature continuous transition to a magnon-crystal is expected to be generic for spin models in dimension $D>1$ where flat-band multi-magnon ground states break translational symmetry.
Sc3Mn3Al7Si5 is a correlated metal in which the Mn moments form a kagome lattice that can frustrate magnetic interactions and no magnetic order develops to the lowest measured temperatures. We have studied the phonon density of states (DOS) in Sc3Mn3Al7Si5 using both inelastic neutron scattering (INS) measurements and ab initio calculations. Above 10 meV, the INS data are dominated by phonon scattering, with peak positions and intensities well described by ab initio simulations of the one-phonon DOS. This indicates phonon anharmonicity is not significant in this material. The partial phonon DOS calculation shows neutron scattering is mainly sensitive to Sc ({sigma}_scatt=23.5 barn), while Mn ({sigma}_scatt=2.15 barn) make only a small contribution. The lattice component of the specific heat is estimated from the measured phonon DOS, and excellent agreement with the measured specific heat from 30 K to 300 K is found, including contributions from lattice dilation and the Sommerfeld coefficient, which are linear in temperature.
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