A method to determine contributions to the hyperfine field at Ce probes in magnetic hosts: Application to Ce impurities at RE sites in REAg (RE = Gd, Tb, Dy, Ho) compounds

Abstract

In this paper, a model based on the molecular field theory is used to fit experimental data of the magnetic hyperfine field (mhf) at nuclei of a magnetic dilute impurity in a magnetic host and determine separately the contributions of the host and the impurity to mhf, which otherwise would not be possible. The model is used to fit data on the temperature dependence of mhf at 140Ce nuclei as an impurity replacing rare-earth (RE) ions in REAg (RE = Gd, Tb, Dy, Ho) hosts. Experimental data on GdAg and DyAg are available in the literature and data on the temperature dependence of mhf for TbAg and HoAg were measured by perturbed gamma–gamma angular correlation (PAC) spectroscopy. Due to the magnetic interplay between host and impurity magnetic ions, the behavior of the temperature dependence of mhf below respective TN of each compound shows an accentuated deviation from an expected Brillouin-like pattern for each compound. This unusual behavior is a consequence of an additional magnetic interaction which emerges from the polarization of localized moments of Ce induced by the magnetic field from RE ions. The impurity contribution calculated from the model are shown to follow the same behavior of the reduced hyperfine field determined from experimental data. The host contribution is discussed in terms of the indirect magnetic coupling between the magnetic RE ions of the host and the obtained values are supported by first-principles calculations based on the density functional theory (DFT). It is also shown that both contributions calculated by the model have values within the expected experimental systematic. Moreover, density of states (DOS) from first-principles calculations explain the mechanism responsible by the observed anomalous behavior of the temperature dependence of mhf. The model presented here can be applied to understand the complex phenomenon of interactions between the magnetic ions of a ordered host and dilute magnetic impurity atoms. The physical description of these magnetic interactions might have an important impact to new applications in spintronics and quantum computing.