Department of Physics, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
J Phys Condens Matter. 2010 Jun 9;22(22):226003. doi: 10.1088/0953-8984/22/22/226003. Epub 2010 May 12.
The hexagonal layered compound, EuPtP, exhibits two valence transitions, at T₁ = 235 K and T₂ = 190 K, and an antiferromagnetic order at T(N) = 8.6 K. We have examined the effects of magnetic field and pressure, and the specific heat. Analysis of the high-field experiments confirms that half of Eu are in a divalent state at the lowest temperature, and that the number of Eu(² + ) increases discontinuously at T₂ and T₁ with increasing temperature. The magnetic entropy reaches ~ 22 J K⁻¹ mol⁻¹ at room temperature, which is larger than that expected for J = 7/2 of Eu(²+ ) (17.3 J K⁻¹ mol⁻¹). This is in good agreement with the magnetic entropy deduced from the interconfigurational fluctuation model, which explains the valence transition in Eu(Pd(₁- x)Pt(x))₂Si₂. The application of pressure shifts T₁ and T₂ higher and suppresses the intermediate phase (β phase, T₂ < T < T₁), whereas it does not change the properties of the low-temperature phase (γ phase, T < T₂) and the T(N).
六方层状化合物 EuPtP 在 T₁=235 K 和 T₂=190 K 处发生两个价态转变，并在 T(N)=8.6 K 处呈现反铁磁有序。我们研究了磁场和压力以及比热的影响。对高场实验的分析证实，在最低温度下，Eu 的一半处于二价态，并且随着温度的升高，Eu(²⁺)的数量在 T₂和 T₁处不连续增加。在室温下，磁熵达到约 22 J K⁻¹ mol⁻¹，大于 Eu(²⁺)的 J=7/2 时的预期值（17.3 J K⁻¹ mol⁻¹）。这与从组态混合模型推断的磁熵非常吻合，该模型解释了 Eu(Pd(₁- x)Pt(x))₂Si₂中的价态转变。压力的施加会使 T₁和 T₂升高，并抑制中间相（β相，T₂< T < T₁），但不会改变低温相（γ相，T < T₂）和 T(N)的性质。
