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

The hexagonal layered compound, EuPtP, exhibits two valence transitions, at T₁ = 235K and T₂ = 190K, and an antiferromagnetic order at T_N = 8.6K. 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 ∼ 22JK^{- 1}mol^{- 1} at room temperature, which is larger than that expected for J = 7/2 of Eu^{2 +} (17.3 JK^{- 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.