Paramagnetic resonance of Gd3+ as a probe of exchange and crystal-field effects in rare-earth-metal pnictides: Antiferromagnetic and diluted materials

We have extended the previous study of electron paramagnetic resonance (EPR) of dilute Gd3+ impurities in Van Vleck paramagnets to study related antiferromagnetic compounds. The host systems studied are the terbium monopnictides and the cerium monopnictides. We have studied both pure host systems and systems with the host rare-earth metal diluted with yttrium. Since the Gd3+ EPR linewidths are often substantial compared to the resonance field, we have included the antiresonance (negative-frequency) effect in the analysis. The Gd3+ resonance g factor serves to probe the host susceptibility. Of particular interest in this regard is the g-factor behavior for TbP as the host system. This agrees quite closely with the superconducting quantum interference device magnetometer susceptibility behavior (i.e., in extremely small magnetic field) found by Koetzler et al., showing that the EPR g factor obtained indeed measures the linear response of the host system. This effect should be useful for studying systems such as CeSb where the apparent susceptibility, as conventionally measured, is likely to include substantial nonlinear contributions. The linewidth behavior is complex. Fluctuation effects among host crystal-field levels sometimes dominate, and this allows the host crystal-field splitting to be determined