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Magnetism
Spin state of Co$^{3+}$ ions in EuBaCo$_{2-x}$O$_{5.5-\delta}$ in the paramagnetic temperature range
T. I. Arbuzova,
S. V. Naumov,
S. V. Telegin Institute of Metal Physics, Ural Division of the Russian Academy of Sciences, Ekaterinburg
Abstract:
The magnetic studies of EuBaCo
$_{2}$O
$_{5.50}$, EuBaCo
$_{1.93}$O
$_{5.40}$, and EuBaCo
$_{1.9}$O
$_{5.36}$ have been performed. Layered cobaltites EuBaCo
$_{2-x}$O
$_{5.5-\delta}$ demonstrated the ferrimagnetic ordering in the temperature range 200 K
$<T<$ 650 K. The ferromagnetic Curie temperature
$T_C$ almost did not change as the number of Co
$^{3+}$–O–Co
$^{3+}$ bonds decreased. The contributions of the ferro- and antiferromagnetic interactions were nearly the same and determine the relationship
$T_{C}>T_{N}$ and
$T_{C}<T_{N}$. At
$T>T_C$, the antiferromagnetic order was retained in the EuBaCo
$_{1.90}$O
$_{5.36}$. As temperature increased, EuBaCo
$_{2-x}$O
$_{5.5-\delta}$ conserved the IS state in pyramids, and gradual LS
$\to$ IS
$\to$ HS transitions occurred in octahedron sites. The increase in the effective magnetic moment
$\mu_{\operatorname{eff}}$ in EuBaCo
$_{1.90}$O
$_{5.36}$ at
$T>$ 580 K demonstrated the transition of Co
$^{3+}$ ions to the HS state at lower temperatures as compared to the EuBaCo
$_{2}$O
$_{5.5}$ stoichiometric composition, and the structural distortions and the increase in the unit cell volume favored to this transition.
Received: 02.08.2016
DOI:
10.21883/FTT.2017.03.44162.314