Switching from unusual to usual ferromagnetism in “112” LnBaCo2O5.50±δ: By calcium doping

On the Location of Host Ca Atoms Responsible for Ferrimagnetism in the Layered Cobaltites YBaCo2O5.5

“…7 The present samples were prepared under identical conditions of temperature, time, and oxygen flow; and therefore, we expect the same oxygen stoichiometry (δ ≃ 0.47 − 0.5). This was confirmed by the magnetic and electrical characterization (not shown) in excellent agreement with our previously published results, 6,7 as well as those from M. Seikh et al 23 and Sarkar et al 11 Having said this, let us now examine the valence state of cobalt. It has been proposed that, even when the nominal valence of Co is 3+, there must exist a disproportionation into Co 2+ and Co 4+ , possibly located near the Ca atoms, for the Co 3+ −O−Co 4+ FM superexchange interactions to account for the ferrimagnetic/AFM competition observed.…”

“…Our neutron diffraction studies led us to propose for the parent compound (x = 0) a two-phase scenario, which was later confirmed by other authors. 8,9 Other recent reports on substituted cobaltites 11,12,21,23,24 have opened up the possibility that the substitution site for Ca atoms might not be obvious. Motin Seikh et al 23 presented a study of the (Y 0.9 Ca 0.1 )BaCo 2 O 5.5 compound showing very similar magnetic properties as our Y(Ba 0.9 Ca 0.1 )Co 2 O 5.5 samples.…”

“…8,9 Other recent reports on substituted cobaltites 11,12,21,23,24 have opened up the possibility that the substitution site for Ca atoms might not be obvious. Motin Seikh et al 23 presented a study of the (Y 0.9 Ca 0.1 )BaCo 2 O 5.5 compound showing very similar magnetic properties as our Y(Ba 0.9 Ca 0.1 )Co 2 O 5.5 samples. More recently, Sarkar et al 11 took one step further and compared both cases, studying samples with the two possible nominal substitution sites.…”

Thermal expansion of layered cobaltites Y(Ba1 −xSrx)Co2O5 + δwithx= 0, 0.05 and 0.10

“…The layered cobaltites RBaCo 2 O 5+δ (R being a rare earth or yttrium) are a family of magnetic oxides which present a very rich variety of phenomena such as spin state order [1][2][3][4][5][6][7], spin state transitions [8,9], metal-insulator transition [10][11][12], magnetic phase coexistence [7,[13][14][15], oxygen non-stoichiometry, etc. Their physical properties depend on the interplay of factors such as R cation size, δ value, vacancy arrangements and disorder introduced by doping with different cations, such as Ca and Sr [13,16,17].…”

Comparison of magnetic and thermoelectric properties of (Nd,Ca)BaCo2O5.5 and (Nd,Ca)CoO3

“…9 The same substitution for intermediate-size europium in EuBaCo 2 O 5.5Àd extends the ferromagnetism down to 10 K and with increasing T C up to 320 K, but does not affect the metal-insulator transition temperature. 10 R 1Àx Ca x BaCo 2 O 5þd with other intermediate-size R ions (Y, Gd, and Sm) demonstrate similar behavior with a negligible change of T C for R ¼ Y and that the change of T C increases with the ionic size of R. 11 In comparison, of simple R 1Àx A x CoO 3 perovskites, where R ¼ La, Pr, Nd, A ¼ Ba, Sr, Ca, Nd 1Àx Ca x CoO 3 demonstrates the most pronounced enhancement of the Seebeck coefficient, 12 which is promising for thermoelectric applications.…”