Temperature dependence of electric field gradient in LaCoO₃perovskite investigated by perturbed angular correlation spectroscopy

Abstract

The time differential perturbed angular correlation (TDPAC) technique was used to study the temperature dependence of electric field gradient (EFG) in LaCoO 3 perovskite using 111 In → 111 Cd and 181 Hf → 181 Ta nuclear probes. The radioactive parent nuclei 111 In and 181 Hf were introduced into the oxide lattice through a chemical process during sample preparation and were found to occupy only the Co sites in LaCoO 3 . The PAC measurements with 111 Cd and 181 Ta probes were made in the temperature range of 4.2-1146 K and 4.2-1004 K, respectively. No long-range magnetic order was observed up to 4.2 K. The EFGs at 111 Cd and 181 Ta show very similar temperature dependences. They increase slowly between 4.2 and about 77 K and then decrease almost linearly with increasing temperature until about 500-600 K, where a broad peak-like structure is observed, followed by linear decrease at still higher temperatures. These discontinuities at about 77 K and 500-600 K have been interpreted as thermally activated spin state transitions from the low-spin (t 6 2g e 0 g ) ground state configuration to the intermediate-spin (t 5 2g e 1 g ) state and from the intermediate-spin to the high-spin (t 4 2g e 2 g ) state of the Co 3+ ion, confirming previous observation in other recent studies. An indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.

Temperature dependence of electric field gradient in TbCoO3

“…These discontinuities are seen more clearly for the data taken with 111 Cd probe at Co sites. Similar discontinuities were also observed in PAC measurements in LaCoO 3 [4] and were attributed to thermally induced spin state transition in Co atoms from low-spin (LS) nonmagnetic state (t 6 2g e 0 g ) to an intermediate-spin (IS) state (t 5 2g e 1 g ) and then from the intermediate-spin (IS) state to high-spin (HS) state (t 4 2g e 2 g )respectively. In the present case transition from LS or IS state to HS state was observed in a wide Fig.…”

“…The observed quadrupole frequencies at 77 K ν Q = 133(1) MHz (η = 0.14) and ν Q = 44.4(4) MHz (η = 0.47) were associated to 111 Cd probe nuclei at Tb and Co sites, respectively. This assignment is based on results of previous PAC results for several rare-earth perovskites [4,6,8]. The measurements with 181 Ta probe showed a single fraction with well-resolved quadrupole interaction, which was associated to 181 Ta at Co sites.…”

“…Recently, theoretical calculations as well as experimental work [2,3] in LaCoO 3 have reported that the transition from low to high spin configurations occurs through an intermediate spin state (t 4 2g e 2 g ). Other RCoO 3 perovskites exhibit an insulator to metal transition at 500-700 K, witch was associated with a transition from the IS state to HS state [4,5]. It would be therefore interesting to investigate other rare earth cobaltite using a sensitive local technique in order to search for spin transitions.…”

Investigation of hyperfine interactions in RMO 3 (R = La, Nd; M = Cr, Fe) antiferromagnetic perovskite oxides using PAC spectroscopy

“…These interactions were assigned to 181 Ta probe nuclei occupying Cr(Fe) sites. The assignments are based on evidence obtained from previous PAC studies of LaCrO 3 and LaFeO 3 and LaMnO 3 [5,6]. From the results of magnetic interactions in LaCrO 3 , LaFeO 3 it was concluded that the spin density transferred from the nearest Cr 3+ (Fe 3+ )ions to rare-earth sites in super exchange interaction should be much smaller than to Cr or Fe sites.…”

Investigation of hyperfine interactions in GdCrO3 perovskite oxide using PAC spectroscopy

“…These interactions were attributed to 181 Ta probe nuclei occupying Cr sites. The assignment is based on the evidence obtained in a previous PAC study of La(Cr,Fe,Mn)O 3 perovskites [7,8]. From the magnetic interactions observed in La(Cr,Fe)O 3 it was concluded that the spin density transferred from the nearest Cr 3+ (Fe 3+ ) ions to rare-earth atom site via oxygen orbital in super exchange interaction is much smaller compared to the Cr or Fe sites.…”