Pressure Effect on the Anomalous Phase Transition in CeOs2Al10

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We report the pressure effects on the anomalous phase transition at T_{0} = 28.5 K in CeOs2Al10 by means of magnetic susceptibility \chi, resistivity \rho, and Hall coefficient measurements. With increasing pressure, the activation energy in \rho(T) at T > T_{0} decreased steeply, while that at T < T_{0} gradually approaches zero at P_{\text{c}} = 2.5 GPa. By contrast, T_{0} is almost constant up to 2 GPa and disappears suddenly at P_{\text{c}}. These observations are at variance with the pressure response of a conventional charge-density-wave transition and an antiferromagnetic order arising from RKKY-type interaction. The phase transition manifests itself in a distinct jump of \mathrm{d}(\chi T)/\mathrm{d}T at T_{0}, which is proportional to the magnetic contribution of the specific heat. The jump linearly decreases to zero as pressure is increased to P_{\text{c}}, suggesting the decrease in the magnetic entropy associated with the transition. It is indicated that the volume fraction of the ordered phase decreases linearly with pressure and vanishes at P_{\text{c}}, where T_{0} suddenly disappears.
2011-06-15