Structure and magnetic properties of rare earth garnets

Author

Milan R. Kokta, New Jersey Institute of Technology

Document Type

Dissertation

Date of Award

Spring 6-30-1972

Degree Name

Doctor of Engineering Science in Chemical Engineering

Department

Chemical Engineering and Chemistry

First Advisor

Lawrence Suchow

Second Advisor

Donald G. Lambert

Third Advisor

Raj Pratap Misra

Fourth Advisor

Ching-Rong Huang

Fifth Advisor

Avner Shilman

Abstract

This study deals with preparation and magnetic properties of garnet compounds containing rare earth ions and scandium ions on two crystallographic sites: the dodecahedral and the octahedral. A number of compounds of the types {R_3-yr_y}[r_x Ga_2-x](Ga₃) O_12' {R₃}[Sc₂](Fe_z Ga_3-x) O_12' {R_3-y Sc_y}[Sc₂] (Fe₃) O_12' and {R_3-y r_y)[r₂ (Fe_z Ga_3-z) O_12' where R stands for large rare earth ions such as Nd³⁺ and Pr³⁺, r stands for small rare earth ions such as Lu³⁺, Yb³⁺, Tm³⁺, Er³⁺, Ho³⁺, and Dy³⁺, was prepared. Distribution of rare earth ions was studied in rare earth gallium garnets in order to determine limits of existence of gallium garnets with both dodecahedral and octahedral sites fully occupied by rare earth ions. Attempts were made to replace tetrahedrally coordinated gallium in such compounds by trivalent iron ions. In addition, attempts were made to prepare rare earth iron garnet compounds with iron fully replaced by scandium on the octahedral sites.

All preparations were made by solid state reactions among oxides of pertinent ions at elevated temperatures. The results of reactions were checked by X-ray diffraction. Compositions of reactant mixtures were varied until single phase compounds were obtained. Single phase compounds were subjected to magnetic measurements. Magnetic susceptibilities as functions of temperature were measured with a Faraday apparatus, and Curie constants were calculated and compared with theoretical values.

In studies of ionic distribution, it has been found that the placement of large rare earth ions such as Nd³⁺ or Pr³⁺ on the dodecahedral sites opens up the lattice so that small rare earth ions may enter the octahedral sites. For cases where the small rare earth was Lu, single phase garnets {R₃} [r₂] (Ga₃)O₁₂ were prepared. To prepare single phase compounds with r ions larger than Lu³⁺, it was necessary to place simultaneously determined minimum amounts off( r in the dodecahedral positions according to the general formula {R_3-y r_y}[r₂](Ga₃)O₁₂. Required minimum value of y increases as the difference in ionic radii of ions occupying the dodecahedral and the octahedral sites decreases. Trends found in iron systems were consistent with these findings. The results of magnetic measurements indicate paramagnetic behavior for all garnets which do not contain iron ions. Results of measurements on garnet compounds where the tetrahedral sites contain iron at least to some extent show more complicated magnetic behavior where ferrimagnetic interactions are more likely to be expected.

Recommended Citation

Kokta, Milan R., "Structure and magnetic properties of rare earth garnets" (1972). Dissertations. 1283.
https://digitalcommons.njit.edu/dissertations/1283