Speaker
Description
We study the magnetic properties of the metallic kagome system (Fe$_{1-x}$Co$_x$)Sn by a combination of $\mu$SR, magnetic susceptibility and STM measurements, in single crystal specimens with Co concentrations $x=0,0.11,0.8$. In FeSn, we find possible signatures for a previously unidentified phase that sets in at $T^*\sim 50$ K, well beneath the Neel temperature $T_N \sim 376$ K, as indicated by a peak in the relaxation rate $1/T_1$ observed in ZF and LF $\mu$SR measurements, with a corresponding anomaly in the ac and dc-susceptibility, and an increase in the static width $1/T_2$ in ZF measurements. No signatures of spatial symmetry breaking are found in STM down to $7$ K. In Fe$_{0.89}$ Co$_{0.11}$Sn, where disorder eliminated the field-cancellation effect, all the implanted muons exhibit precession and/or relaxation in the ordered state. In Fe$_{0.2}$Co$_{0.8}$Sn, we find canonical spin glass behavior with freezing temperature $T_{g} \sim 3.5~K$; the ZF and LF time spectra exhibit results similar to those observed in dilute alloy spin glasses CuMn and AuFe, with a critical behavior of $1 / T_{1}$ at $T_{g}$ and $1 /T_{1}\rightarrow$ as $T \rightarrow 0$. The absence of spin dynamics at low temperatures makes a clear contrast to the spin dynamics observed by $\mu$SR in many geometrically frustrated spin systems. The spin glass behavior is shown to originate primarily from the randomness of doped Fe moments rather than due to geometrical frustration of the underlying lattice.
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