Magnetic Behavior of Cobalt in Garnets. I. Spin Resonance in Cobalt-Doped Yttrium Gallium Garnet

Abstract

We have studied the spin resonance at 24 and 56 kMc/sec of cobalt in single crystals of yttrium gallium garnet (YGaG). We find resonances associated with four different combinations of site and charge state. Tetrahedral Co 2+ has the M 2 ground term with the tetragonal splitting parameter 2J9= -36 cm -1 . Octahedral Co 2+ has the 4 7\ ground term with the trigonal splitting A t = +650 cm -1 . It is seen in otherwise pure YGaG, as well as in crystals counterdoped with Si 4+ . Tetrahedral Co 3+ has the 5 E ground term, with Z>^14 cm -1 , |»| =0.66 cm -1 . This value of a, the fourth-order cubic field-splitting parameter, is exceptionally large and makes possible strong magnetic-dipole transitions between states with S z~± :2. Electric-dipole transitions are also observed between these states. Octahedral Co 4+ has the strong-field 2 Ti ground term, with A* = +1000 cm -1 ; its spectrum is very weak relative to Co 3+ , even in crystals counterdoped with Ca 2+ . The absence of a resonance from octahedral Co 3+ implies that this ion has the strong-field l A i ground term. Cobalt does not appear to enter the dodecahedral site in our crystals. Our results are complementary to, and on the whole consistent with, the optical data of Wood and Remeika. We review the information available on crystal fields at the octahedral and tetrahedral sites in garnet, and on the hyperfine structure of cobalt.

Magnetic anisotropy in geometrically frustrated kagome staircase lattices

“…[20,21]) nevertheless, the results obtained confirm significant contribution of single-ion mechanism to the effective magnetic anisotropy in Co 3 V 2 O 8 single crystals.…”

Theoretical studies of the spin-Hamiltonian parameters and their stress dependences for Ru3+ and Ir4+ ions in Y3Ga5O12 crystals

“…The parameter v is much more sensitive to the trigonal distortion angleť han to the bonding length R. So, we only consider the local angular compressibility dˇ/dP here. Under the stress P||C 3 axis, we haveˇ(P) =ˇ+ (dˇ/dP)P. From the observed stress dependences (dg ⊥ /dP) ≈ 2.4 and 1.5 × 10 −12 dyn −1 cm 2 for Ru 3+ and Ir 4+ in YGG [12], respectively, we obtain dď P ≈ −1.10 × 10 −13 and − 2.09 × 10 −13 rad dyn −1 cm 2 (9) for YGG:Ru 3+ and YGG:Ir 4+ , respectively. The comparisons between the calculated and observed dg ⊥ /dP for both systems are shown in Table 1.…”

“…According to crystal-field theory, the perturbation formulas of SH parameters based on the one-SO-parameters model for the lowspin d 5 ions in a trigonally distorted octahedron read [9,10,13]:…”

“…So, the defect natures and defect structures of TM ions in garnets attract much attention. Since the EPR spectra of TM ions in crystals are sensitive to their immediate environments and hence to the defect natures and structures, many EPR investigations have been made for TM ions in garnets [1,3,[5][6][7][8][9][10][11][12]. Among them, the EPR studies for the 3d n TM ions are much more than those for the 4d n and 5d n ions in garnets.…”

Spin-Hamiltonian parameters and off-center displacements for Rh4+and Ir4+ions in rhombohedral BaTiO3

“…The trigonal crystal field splits the 2 T 2 state into the 2 E and 2 A 1 states, and the energy separation between 2 E and 2 A 1 is characterized by the trigonal field parameter ν. According to the first-order theory of resonance in a 2 T 2 term (9,(15)(16)(17), the spin-Hamiltonian parameters for the low-spin d 5 ions in trigonal symmetry can be expressed as…”