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Register a new userMagnetic behavior of new compounds, Gd3RuSn6 and Tb3RuSn6
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E. V. Sampathkumaran Professor
Publication date
2017
fields
Physics
and research's language is
English
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We report temperature (T) dependence of dc magnetization, electrical resistivity (rho(T)), and heat-capacity of rare-earth (R) compounds, Gd3RuSn6 and Tb3RuSn6, which are found to crystallize in the Yb3CoSn6-type orthorhombic structure (space group: Cmcm). The results establish that there is an onset of antiferromagnetic order near (T_N) 19 and 25 K respectively. In addition, we find that there is another magnetic transition for both the cases around 14 and 17 K respectively. In the case of the Gd compound, the spin-scattering contribution to rho is found to increase below 75 K as the material is cooled towards T_N, thereby resulting in a minimum in the plot of rho(T) unexpected for Gd based systems. Isothermal magnetization at 1.8 K reveals an upward curvature around 50 kOe. Isothermal magnetoresistance plots show interesting anomalies in the magnetically ordered state. There are sign reversals in the plot of isothermal entropy change versus T in the magnetically ordered state, indicating subtle changes in the spin reorientation with T. The results reveal that these compounds exhibit interesting magnetic properties.
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Quantum spin liquids (QSLs) are an exotic state of matter that is subject to extensive research. However, the relationship between the ubiquitous disorder and the QSL behaviors is still unclear. Here, by performing comparative experimental studies on two kagom{e}-lattice QSL candidates, Tm$_3$Sb$_3$Zn$_2$O$_{14}$ and Tm$_3$Sb$_3$Mg$_2$O$_{14}$, which are isostructural to each other but with strong and weak structural disorder, respectively, we show unambiguously that the disorder can induce spin-liquid-like features. In particular, both compounds show dominant antiferromagnetic interactions with a Curie-Weiss temperature of -17.4 and -28.7 K for Tm$_3$Sb$_3$Zn$_2$O$_{14}$ and Tm$_3$Sb$_3$Mg$_2$O$_{14}$, respectively, but remain disordered down to about 0.05 K. Specific heat results suggest the presence of gapless magnetic excitations characterized by a residual linear term. Magnetic excitation spectra obtained by inelastic neutron scattering (INS) at low temperatures display broad continua. All these observations are consistent with those of a QSL. However, we find in Tm$_3$Sb$_3$Zn$_2$O$_{14}$ which has strong disorder resulting from the random mixing of the magnetic Tm$^{3+}$ and nonmagnetic Zn$^{2+}$, that the low-energy magnetic excitations observed in the specific heat and INS measurements are substantially enhanced, compared to those of Tm$_3$Sb$_3$Mg$_2$O$_{14}$ which has much less disorder. We believe that the effective spins of the Tm$^{3+}$ ions in the Zn$^{2+}$/Mg$^{2+}$ sites give rise to the low-energy magnetic excitations, and the amount of the random occupancy determines the excitation strength. These results provide direct evidence of the mimicry of a QSL caused by disorder.
We present electronic structure calculations for the one-dimensional magnetic chain compounds Ca_3CoRhO_6 and Ca_3FeRhO_6. The calculations are based on density functional theory and the local density approximation. We use the augmented spherical wave (ASW) method. The observed alternation of low- and high-spin states along the Co-Rh and Fe-Rh chains is related to differences in the oxygen coordination of the transition metal sites. Due to strong hybridization the O 2p states are polarized, giving rise to extended localized magnetic moments centered at the high-spin sites. Strong metal-metal overlap along the chains leads to a substantial contribution of the low-spin Rh 4d_{3z^2-r^2} orbitals to the exchange coupling of the extended moments. Interestingly, this mechanism holds for both compounds, even though the coupling is ferromagnetic for the cobalt and antiferromagnetic for the iron compound. However, our results allow to understand the different types of coupling from the filling dependence of the electronic properties.
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