EPR spectra and magnetization ofEu2+ions in PbSe

Electron-paramagnetic-resonance (EPR) experiments are performed on ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$Se at room temperature and at liquid-helium temperature to identify the different transitions with respect to the central one (1/2⇆-1/2) and to deduce the effective Landé factor g. We found g=1.982±0.002. The fine structure is in agreement with the crystal-field-level splitting (to second order in perturbation theory). The crystal-field coefficients ${\mathit{b}}_4$ and ${\mathit{b}}_6$ are found to be, respectively, ${\mathit{b}}_4$=+269.2 MHz and ${\mathit{b}}_6$=-2.4 MHz at 4.2 K. Furthermore, forbidden transitions and transitions due to pairs are observed. The analysis of magnetization and susceptibility experiments in terms of a modified cluster model of the ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$Se shows two types of pairs with different interactions: the first type is attributed to ferromagnetic interactions between the ${\mathrm{Eu}}^{2+}$ ions’ nearest neighbors with a constant exchange value of ${\mathit{J}}_1$/${\mathit{k}}_{\mathit{B}}$=+0.52 K, and the second is attributed to antiferromagnetic interactions between next-nearest neighbors with a ${\mathit{J}}_2$/${\mathit{k}}_{\mathit{B}}$=-0.32 K.