Temperature Dependence of the Eu3+ Spin 〈S(T)〉 in EuP

The temperature dependence of the Eu³⁺ spin $\mathrm{〈S(T)〉}$ in the NaCl‐type intermetallic compound EuP has been studied by the observation of the phosphorus nuclear magnetic resonance (NMR) between 100° and 600°K. The phosphorus Knight shift consists of two contributions: (1) a temperature‐independent term K₀ equal to the Knight shift in the nonmagnetic isomorph LaP and (2) a temperature‐dependent term K(T), proportional to the Eu³⁺ spin $\mathrm{〈S(T)〉}$ . The temperature dependence of the Eu³⁺ spin $\mathrm{〈S(T)〉}$ was calculated for a Eu³⁺ ion in an octahedral crystal field and an exchange interaction of the form ${\text{2βH}}_{\mathrm{e\; x}}{\mathrm{S(H}}_{\mathrm{e\; x}}\mathrm{=\lambda 〈S〉)}$ . Good agreement between the calculated and observed temperature dependence of the Knight shift was obtained for E₁ (the energy separation between the J=0 and J=1 states) and λ in the range E₁/k=525°K, λβ/k=0°K to E₁/k=475°K, λβ/k=5°K. An analysis of the Knight shifts showed that these data are relatively insensitive to the effects of the crystal field interaction. Using the uniform‐conduction electron spin‐polarization model for the Knight shift, the resulting s‐f exchange energy for EuP was calculated to be J_sf≃−0.37 eV, in good agreement with the other rare‐earth phosphides.