Zero-field NMR and NQR studies of magnetically ordered state in charge-ordered EuPtP

Abstract

EuPtP undergoes two valence transitions and has two kinds of valence states of Eu ions at low temperatures. In the charge-ordered state, this compound shows an antiferromagnetic order ascribed to magnetic divalent Eu ions. We investigated the antiferromagnetically ordered state of EuPtP by nuclear magnetic resonance (NMR) measurement and nuclear quadrupole resonance (NQR) measurement in a zero external magnetic field. The observed $^{153}\mathrm{Eu}$ NMR signals of a magnetic divalent state and $^{151,153}\mathrm{Eu}$ NQR signals of a nonmagnetic trivalent state clearly demonstrate that the spins order in the hexagonal basal plane and the internal magnetic field is not canceled out, even at the ${\mathrm{Eu}}^{3+}$ layers which are in the middle of magnetic ${\mathrm{Eu}}^{2+}$ layers. In addition, the observation of ${}^{31}\mathrm{P}$ and $^{195}\mathrm{Pt}$ NMR spectra allowed us to discuss a possible magnetic structure. We also evaluated the nuclear quadrupole frequencies for both ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}$ ion states.