Physical properties of CeIrSi with trillium-lattice frustrated magnetism

Magnetic $\left(\chi \right)$, transport $\left(\rho \right)$, and heat capacity $\left(C_{\mathrm{m}}\right)$ properties of CeIrSi are investigated to elucidate the effect of geometric frustration in this compound with trillium type structure because, notwithstanding its robust effective moment, ${\mu }_{\mathrm{eff}}\approx 2.46{\mu }_{\mathrm{B}}$, this Ce-lattice compound does not undergo a magnetic transition. In spite of that it shows broad $C_{\mathrm{m}}\left(T\right)/T$ and $\chi \left(T\right)$ maxima centered at $T_{\max }\approx 1.5$ K, while a $\rho \propto T^2$ thermal dependence, characteristic of electronic spin coherent fluctuations, is observed below $T_{\mathrm{coh}}\approx 2.5$ K. Magnetic field does not affect significantly the position of the mentioned maxima up to $\approx 1$ T, though $\chi \left(T\right)$ shows an incipient structure that completely vanishes at ${\mu }_{0}H\approx 1$ T. Concerning the $\rho \propto T^2$ dependence, it is practically not affected by magnetic field up to ${\mu }_{0}H=9$ T, with the residual resistivity ${\rho }_0\left(H\right)$ slightly decreasing and $T_{\mathrm{coh}}\left(H\right)$ increasing. These results are compared with the physical properties observed in other frustrated intermetallic compounds.

Figure 1

Rietveld refinement of x-ray intensity data of CeIrSi. Very small amounts of ${\mathrm{CeSi}}_{2-x}$ and ${\mathrm{CeIr}}_2{\mathrm{Si}}_2$ are almost invisible (green bars below spectrum). The inset depicts the atom arrangement as well as the Ce-Ce next nearest neighbor configuration (trillium lattice).

Figure 2

Inverse susceptibility, continuous curve represents the fit according to Eq. (1). Inset: Analysis of the spurious ferromagnetic contribution below 10 K. Continuous curve shows the fit with the ${M/H|}_{\mathrm{spur}}$ heuristic function described in the text.

Figure 3

(a) Low temperature magnetic susceptibility evaluated as $M/H\left(T\right)$ performed under relatively weak magnetic fields. The arrows indicate the two anomalies described in the text. The curves are shifted due to the effect of the FM contribution that arises at $T<11$ K. (b) Low temperature magnetization measurements of CeIrSi.

Figure 4

Temperature and field dependent electrical resistivity measurements on CeIrSi. The inset shows the low temperature range between 0 and 12 K revealing coherent spin scattering at low temperature.

Figure 5

(a) Low temperature magnetic contribution $C_{\mathrm{m}}\left(T\right)/T$ up to 20 K and (continuous curve) comparison with theoretic prediction for a trillium-type lattice [18]. Inset: (left axis) Measured specific heat $C_P\left(T\right)/T$ of CeIrSi and LaIrSi up to 90 K and (right axis) entropy variation $S_m\left(T\right)$ normalized to a doublet GS $Rln\left(2\right)$. (b) High temperature $C_{\mathrm{m}}\left(T\right)/T$ of CeIrSi showing the analysis for GS and two excited level contributions (see the text). Error bars are representative of the uncertainty of the $C_P\left(T\right)$ measurements.

Figure 6

(a) Comparison between $\chi \left(T\right)$, $C_{\mathrm{m}}\left(T\right)/T$, and $\rho \left(T\right)$ at $T<3$ K. (b) Specific heat dependence of CeIrSi in magnetic field up to ${\mu }_{0}H=8$ T. Continuous curve: Guide to the eyes tracing the $C_{\mathrm{m}}(T,H)/T$ maxima.

Figure 7

Double logarithmic representation showing the thermal dependence of $C_{\mathrm{m}}\left(T\right)/T$ above the maximum and the corresponding power-law fit (solid curve). Inset: Thermal dependence of the entropy compared with the extrapolation of $S_{\mathrm{fit}}\left(T\right)$ to zero (solid line) at finite temperature.