Properties of rare-earth iron garnets from first principles

Abstract

Structural and magnetic properties of rare-earth iron garnets (RIG), which contain 160 atoms per unit cell, are systematically investigated for rare-earth elements varying from La to Lu (and including Y), by performing spin polarized density-functional calculations. The effects of 4f electrons (as core or as valence electrons) on the lattice constant, internal coordinates and bond lengths are found to be rather small, with these predicted structural properties agreeing rather well with available experiments. On the other hand, treating such electrons as valence electrons is essential to interpret the total magnetization measured in some RIG at low temperature, the different orientation and magnitude of the magnetizations that Fe and rare-earth ions can adopt and to also explain why some RIG have a compensation temperature while others do not. The magnetic exchange couplings and orbital-projected density of states are also reported for two representative materials, namely Gd3Fe5O12 and Nd3Fe5O12, when accounting for their 4f electrons.

In-field 57Fe M$\ddot {o}$ssbauer spectroscopy study of polycrystalline rare-earth iron garnet (R3Fe5O12; R=Y, Gd, Ho, Tm, & Yb) compounds

“…The crystallite size calculated using Scherrer formula [18] for all the samples is in the range of 60-65 nm. The obtained lattice parameters are shown in Table 1, matching with the literature [6,19].…”

“…The unit cell of RIG contains eight formula units composed of 24 R 3+ ions at dodecahedral (c-) sites, 24 Fe 3+ ions at tetrahedral (d-) sites, 16 Fe 3+ ions at octahedral (a-) sites and 96 O 2ions at (h-) sites, a total of 160 atoms. The strongest superexchange interaction between a-and d-sites results in magnetization of these sites (M d and M a ) to be anti-parallel resulting in a very high ferri to paramagnetic transition Curie temperature (T C ≈ 550±10K), corresponding to, which is approximately same for all RIG regardless of R ions at c-site [5,6].…”

Atomic-scale origin of ultrahigh piezoelectricity in samarium-doped PMN-PT ceramics

“…DFT calculations are carried out using the Vienna ab initio simulation package (VASP) [39]. Notably, the 4 f electrons of rare earth are not treated as valence electrons, since we are not dealing with magnetism here and the structural properties are not sensitive to 4 f electrons [40,41]. Details about the experiments and calculations can be found in the Supplemental Material [26].…”

Atomic-scale insights into quantum-order parameters in bismuth-doped iron garnet

“…The electronic structure was calculated using density functional theory, implemented in the Vienna ab initio simulation package (VASP) (55,56). Projector augmented wave pseudopotentials (57) and the generalized gradient approximation (GGA) for the exchange correlation interaction were used (20,58). Due to the complexity and time consumption of density functional theory (DFT) calculations when substituent elements are considered in strongly correlated iron garnet with large numbers of atoms, Bi-substituted lutetium iron garnet of different Bi/Lu ratio, and unsubstituted samples were each built as a primitive unit cell containing 80 atoms.…”

“…The strength of the Faraday effect, which describes a rotation of the plane of polarization of electromagnetic radiation in a magnetic field, is linearly proportional to the Verdet constant (13,14) for a given material, which for magneto-optical materials such as substituted garnets depends strongly on the coupling effect of multiple quantumorder parameters (15,16), including those of lattice, spin, and electronic orbitals (12,17,18). In particular, diverse polyhedral sites in the garnet structure are bridged via oxygen atoms with a strong exchange interaction effect, resulting in complex electronic and crystal structures (19)(20)(21)(22). Although pure yttrium iron garnet (YIG) has several advantages in terms of magneto-optical response, it has not been widely applied in integrated devices due to its low Verdet constant, resulting in a limited Faraday rotation (23,24).…”