Revealing Site Occupancy in a Complex Oxide: Terbium Iron Garnet

Abstract

Complex oxide films stabilized by epitaxial growth can exhibit large populations of point defects which have important effects on their properties. The site occupancy of pulsed laser-deposited epitaxial terbium iron garnet (TbIG) films with excess terbium (Tb) is analyzed, in which the terbium:iron (Tb:Fe) ratio is 0.86 compared to the stoichiometric value of 0.6. The magnetic properties of the TbIG are sensitive to site occupancy, exhibiting a higher compensation temperature (by 90 K) and a lower Curie temperature (by 40 K) than the bulk Tb 3 Fe 5 O 12 garnet. Data derived from X-ray core-level spectroscopy, magnetometry, and molecular field coefficient modeling are consistent with occupancy of the dodecahedral sites by Tb 3+ , the octahedral sites by Fe 3+ , Tb 3+ and vacancies, and the tetrahedral sites by Fe 3+ and vacancies. Energy dispersive X-ray spectroscopy in a scanning transmission electron microscope provides direct evidence of Tb Fe antisites. A small fraction of Fe 2+ is present, and oxygen vacancies are inferred to be present to maintain charge neutrality. Variation of the site occupancies provides a path to considerable manipulation of the magnetic properties of epitaxial iron garnet films and other complex oxides, which readily accommodate stoichiometries not found in their bulk counterparts.

Temperature Evolution of Magnon Propagation Length in Tm3Fe5O12 Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping

“…Our observation strongly hints at the presence of only one Fe oxidation state, namely the Fe 3+ ion, and hence, we can rule out the contribution of single ion anisotropy of Fe 2+ ions toward the increased magnetic anisotropy. This is also in agreement with recent studies on Tb-rich TbIG thin films , which reveal very low Fe 2+ ion concentrations. Therefore, the increase in H K eff below 200 K in the TmIG films may arise from single-ion anisotropies of the Tm 3+ and Fe 3+ ions as well as from the enhanced contributions of K 1 and K me toward K eff at low temperatures. − …”

“…The decrease in M S at low T is well-known in TmIG , and is a result of the increasing moment of the Tm 3+ ion at low T , which competes with the net moment of the Fe 3+ ions (i.e., the dodecahedral Tm 3+ moment opposes the net moment of the tetrahedral and octahedral Fe 3+ moments). Based on the molecular-field-coefficient theory developed by Dionne, we have performed molecular-field simulations , to determine M S ( T ) for TmIG (see Supplementary Figure 3n) which is consistent with our experimental observation of the decrease in M S at low T . It is apparent from Figure c,d that the temperature evolution of V ISHE signal follows that of M S .…”

Atomic order of rare earth ions in a complex oxide: a path to magnetotaxial anisotropy

“…A series of (Eu x Tm 1- x ) 3 IG films with a thickness of 16–40 nm were grown on (111) GGG by pulsed laser codeposition 27 . By fitting the high-resolution X-ray diffraction (HRXRD) symmetric scans about the (444) reflection (Fig.…”