Pressure and magnetic field dependence of valence and magnetic transitions in EuPtP

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).