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Register a new userMagnetic interactions in the tripod-kagome antiferromagnet Mg$_{2}$Gd$_{3}$Sb$_{3}$O$_{14}$ probed by static magnetometry and high-field ESR spectroscopy
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We report an experimental study of the static magnetization $M(H,T)$ and high-field electron spin resonance (ESR) of polycrystalline MgGd, a representative member of the newly discovered class of the so-called tripod-kagome antiferromagnets where the isotropic Gd$^{3+}$ spins ($S = 7/2$) form a two-dimensional kagome spin-frustrated lattice. It follows from the analysis of the low-$T$ $M(H)$-curves that the Gd$^{3+}$ spins are coupled by a small isotropic antiferromagnetic (AFM) exchange interaction $|J| approx$ 0.3,K. The $M(H,T)$-dependences measured down to 0.5,K evidence a long-range AFM order at $T_{text{N}} = 1.7$,K and its rapid suppression at higher fields $geq 4$,T. ESR spectra measured in fields up to 15,T are analyzed considering possible effects of demagnetizing fields, single-ion anisotropy and spin-spin correlations. While the demagnetization effects due to a large sample magnetization in high fields and its shape anisotropy become relevant at low temperatures, the broadening of the ESR line commencing already at $Tlesssim 30$,K may indicate the onset of the spin-spin correlations far above the ordering temperature due to the geometrical spin frustration in this compound.
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We present a systematic study of the structural and magnetic properties of two branches of the rare earth Tripod Kagome Lattice (TKL) family A$_{2}$RE$_{3}$Sb$_{3}$O$_{14}$ (A = Mg, Zn; RE = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb; here, we use abbreviation textit{A-RE}, as in textit{MgPr} for Mg$_{2}$Pr$_{3}$Sb$_{3}$O$_{14}$), which complements our previously reported work on textit{MgDy}, textit{MgGd}, and textit{MgEr} cite{TKL}. The present susceptibility ($chi_{dc}$, $chi_{ac}$) and specific heat measurements reveal various magnetic ground states, including the non-magnetic singlet state for textit{MgPr}, textit{ZnPr}; long range orderings (LROs) for textit{MgGd}, textit{ZnGd}, textit{MgNd}, textit{ZnNd}, and textit{MgYb}; a long range magnetic charge ordered state for textit{MgDy}, textit{ZnDy}, and potentially for textit{MgHo}; possible spin glass states for textit{ZnEr}, textit{ZnHo}; the absence of spin ordering down to 80 mK for textit{MgEr}, textit{MgTb}, textit{ZnTb}, and textit{ZnYb} compounds. The ground states observed here bear both similarities as well as striking differences from the states found in the parent pyrochlore systems. In particular, while the TKLs display a greater tendency towards LRO, the lack of LRO in textit{MgHo}, textit{MgTb} and textit{ZnTb} can be viewed from the standpoint of a balance among spin-spin interactions, anisotropies and non-Kramers nature of single ion state. While substituting Zn for Mg changes the chemical pressure, and subtly modifies the interaction energies for compounds with larger RE ions, this substitution introduces structural disorder and modifies the ground states for compounds with smaller RE ions (Ho, Er, Yb).
We present the structural and magnetic properties of a new compound family, Mg$_2$RE$_3$Sb$_3$O$_{14}$ (RE = Gd, Dy, Er), with a hitherto unstudied frustrating lattice, the tripod kagome structure. Susceptibility (ac, dc) and specific heat exhibit features that are understood within a simple Luttinger-Tisza type theory. For RE = Gd, we found long ranged order (LRO) at 1.65 K, which is consistent with a 120 $^{circ}$ structure, demonstrating the importance of diople interactions for this 2D Heisenberg system. For RE = Dy, LRO at 0.37 K is related to the kagome spin ice (KSI) physics for a 2D system. This result shows that the tripod kagome structure accelerates the transition to LRO predicted for the related pyrochlore systems. For RE = Er, two transitions, at 80 mK and 2.1 K are observed, suggesting the importance of quantum fluctuations for this putative XY system.
We have studied the ground state of the classical Kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$. Strong magnetic Bragg peaks observed in the $d$-spacing shorter than 6.0 AA were indexed by the propagation vectors of $boldsymbol{k}_{0} = (0,0,0)$. Additional peaks with weak intensities in the range of the $d$-spacing longer than 8.0 AA were indexed by the incommensurate vectors of $boldsymbol{k}_{1}=(0.3209(2),0.3209(2),0)$ and $boldsymbol{k}_{2}=(0.3338(4),0.3338(4),0)$. Magnetic structure analysis exhibits that the 120$^{circ}$ structure with the {it tail-chase} geometry having $boldsymbol{k}_0$ is modulated by the incommensurate vectors. The classical calculation of the Kagome Heisenberg antiferromagnet having the antiferromagnetic 2nd-neighbor interaction, the ground state of which is degenerated 120$^{circ}$ structures with $boldsymbol{k}_0$, reveals that the magnetic dipole-dipole (MDD) interaction including up to the 4th neighbor terms selects the tail-chase structure. The observed modulation of the tail-chase structure is indicated to be due to a small perturbation such as the long-range MDD interaction or the interlayer interaction.
A single crystal S=3/2 perfect kagome lattice antiferromagnet $mathrm{KCr_3(OH)_6(SO_4)_2}$ (Cr-jarosite) has been studied by X-band and high-frequency electron spin resonance (ESR). The g-values perpendicular to the kagome plane (c-axis) and in the plane are determined to be $g_c=1.9704 pm 0.0002$ and $g_xi=1.9720 pm 0.0003$, respectively, by high-frequency ESR observed at 265 K. Antiferromagnetic resonances (AFMR) with the antiferromagnetic gap of 120 GHz are observed at 1.9 K, which is below $T_N$=4.5 K. The analysis of AFMR modes by the conventional molecular field theory shows $d_p=0.27$ K and $d_z=0.07$ K, where $d_p$ and $d_z$ are in-plane and out-of-plane components of DM d vector, respectively. From these results and the estimated exchange interaction J=6.15 K by Okuta et al., the ground state of Cr-jarosite is discussed in connection with the Monte Carlo simulations result with classical Heisenberg spins on the kagome lattice by Elhajal et al. Finally, the angular dependence of linewidth and the lineshape observed at 296 K by X-band ESR show typical behavior of a two-dimensional Heisenberg antiferromagnet, suggesting a good two-dimensionality of Cr-jarosite.
An electron spin resonance (ESR) study of the heavy fermion compound YbRh2Si2 for fields up to ~ 8 T reveals a strongly anisotropic signal below the single ion Kondo temperature T_K ~ 25 K. A remarkable similarity between the T-dependence of the ESR parameters and that of the specific heat and the 29Si nuclear magnetic resonance data gives evidence that the ESR response is given by heavy fermions which are formed below T_K and that ESR properties are determined by their field dependent mass and lifetime. The signal anisotropy, otherwise typical for Yb{3+} ions, suggests that, owing to a strong hybridization with conduction electrons at T < T_K, the magnetic anisotropy of the 4f states is absorbed in the ESR of heavy quasiparticles. Tuning the Kondo effect on the 4f states with magnetic fields ~ 2 - 8 T and temperature 2 - 25 K yields a gradual change of the ESR g-factor and linewidth which reflects the evolution of the Kondo state in this Kondo lattice system.
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