Although a considerable body of data exists on the parametrization of the ground-state splittings of S-state ions in crystals, relatively little progress has been made in obtaining a quantitative understanding of the mechanisms which determine these parameters. In the course of summarizing our present understanding, we emphasize the need for making planned experiments explicitly aimed at testing theoretical models, such as those proposed in this article. The variable frequency E.P.R. technique is described in some detail, as it has proved to be particularly useful in this respect.

Interpretation of S-state ion E.P.R. spectra

Some experimental aspects of spin glasses: A review

Publisher Summary This chapter discusses rare earth pnictides. The rare earth elements are transitional in their chemical properties between the alkaline-earth elements, especially Ba, and the 5d transition elements Hf, Ta. With certain exceptions they behave like transition elements of the Sc group with additional f electrons in discrete levels. The exceptions are mainly because of the high stability of the empty, half- or completely-filled 4f shell. Certain compounds formed by Eu and Yb, in some cases also Sm and Tm, therefore, show close similarities with the corresponding alkaline-earth compounds whereas Ce and Tb in fluorides and oxides resemble Hf4+ and Th4+ compounds. The chapter discusses the preparation of the rare earth pnictides. All lanthanide elements react in the solid state with pnigogen vapors. Except for nitrogen, the chemical reaction takes place at temperatures below the melting point of the elementary pnigogen; therefore, they can be performed in fused-silica tubes. The reaction products are microcrystalline powders, which usually serve only as starting materials for single-crystal growth.

Chapter 33 Rare earth pnictides

Spin-mechatronics [Journal of the Physical Society of Japan, ISSN 0031-9015, Jan 2017, v. 86(1)]

A new EPR determination of the spin-Hamiltonian parameters for Gd3+:YAG has been made. A direct comparison of garnet crystal-field and spin-Hamiltonian parameters, as well as the success of the superposition model analysis, enables us to eliminate the possibility of large non-linear (e.g. quadratic) crystal-field contributions to the Gd3+ ground-state splitting. Spin-Hamiltonian superposition model parameters are derived and an analysis of the n=2 crystal-field and spin-Hamiltonian parameters suggests that the coordinate angles derived from X-ray data are in error by about 1 degrees .

Interpretation of Gd3+ spin-Hamiltonian parameters in garnet host crystals

We have studied the use of paramagnetic resonance of dilute Gd impurities as a probe of exchange and crystal-field effects in the singlet-ground-state systems $\mathrm{Tm}X$ and $\mathrm{Pr}X$ (where $X$ is one of the group-$\mathrm{V}A$ elements, P, As, Sb, Bi), i.e., the thulium and praseodymium monopnictides of NaCl structure. Analysis of the temperature-dependent resonance $g$-value behavior yields values for the Gd-Tm and Gd-Pr exchange interactions. The Gd-Tm exchange changes sign with increasing lattice parameter (on going from the phosphide and arsenide to the antimonide and bismuthide); while the Gd-Pr exchange becomes increasingly negative with increasing lattice parameter. Analysis of the temperature dependence of the linewidth yields values for the crystal-field splitting of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ in agreement with those from neutron scattering. We briefly mention recent experiments using EPR of Gd in TbP to probe the behavior of the staggered susceptibility in the critical region.

Paramagnetic resonance of Gd 3 + as a probe of exchange and crystal-field effects in singlet-ground-state systems

We have extended the previous study of electron paramagnetic resonance (EPR) of dilute Gd/sup 3 +/ 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 Gd/sup 3 +/ EPR linewidths are often substantial compared to the resonance field, we have included the antiresonance (negative-frequency) effect in the analysis. The Gd/sup 3 +/ 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.

Paramagnetic resonance of Gd/sup 3 +/ as a probe of exchange and crystal-field effects in rare-earth-metal pnictides: Antiferromagnetic and diluted materials

K. Sugawara

Papers

Paramagnetic resonance of Gd 3 + as a probe of exchange and crystal-field effects in singlet-ground-state systems

Paramagnetic resonance of Gd/sup 3 +/ as a probe of exchange and crystal-field effects in rare-earth-metal pnictides: Antiferromagnetic and diluted materials

Anomalous resistivity behavior in singlet-ground-state systems