The effect of treatment conditions on the magnetic and magnetotransport properties of A-site ordered
PrBaMn2O6−δ
manganites is examined. The parent oxygen-stoichiometric A-site ordered
PrBaMn2O6
samples were prepared from oxygen-stoichiometric A-site disordered
Pr0.50Ba0.50MnO3
ones by using a ‘two-step’ synthesis method. The most significant
structural feature of the A-site ordered manganites is that the
MnO2
sublattice is sandwiched by two kinds of rock-salt layers,
PrOx
and BaO. The oxygen-stoichiometric A-site ordered
PrBaMn2O6
demonstrates a ferromagnetic metal to paramagnetic insulator transition with
the Curie point at about 320 K. These compounds are stable in air up to
1300 °C. The A-site
ordered PrBaMn2O6
samples were next reduced in flowing argon as well as being treated
under high pressure conditions. The reduction of the A-site ordered
PrBaMn2O6
samples leads to the appearance of an antiferromagnetic state with a
Néel point of about 140 K, while the A-site order remains. Upon high
pressure treatment the degree of A-site order decreases, which reduces
TC
to 180 K. The magnetotransport properties of A-site ordered manganites treated under
different conditions are discussed in terms of the manganese valence, oxygen content and
degree of A-site order.
We report the investigation of a real part of the admittance σ of granular nanocomposites (Fe 0.45 Co 0.45 Zr 0.10) x (Al 2 O 3) 1−x with 0.30 < x < 0.70 in the dielectric (hopping) regime. An analysis of the σ(T, f, x) dependences in the as-deposited and annealed films over the temperature 77 K < T < 300 K and frequency 50 < f < 10 6 Hz ranges displayed the predominance of an activation (hopping) conductance mechanism with dσ/ dT > 0 for the samples below the percolation threshold x C ≈ 0.76 ± 0.05. Based on the earlier models for hopping AC conductance, computer simulation of the frequency coefficient α f of hopping conductance depending on the probability of jump p, frequency f , and also on the shape of σ(f) curve was performed. The experimental and simulation results revealed a good agreement.
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