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Spontaneous ferromagnetism at room temperature in oxygen-rich dicalcium cuprate Ca2CuO3+δ
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Stoichiometric Ca2CuO3, having square-planar Cu-chains [C. L. Teske and H. Müller-Buschbaum, Z. Anorg. Allg. Chem. 379, 234 (1970); M. Hjorth and J. Hyldtoft, Acta Chem. Scand. 44, 516 (1990)], is expectedly antiferromagnetic due to 1D intrachain superexchange [K. Okuda, S. Noguchi, K. Konishi, H. Deguchi, and K. Takeda, J. Magn. Magn. Mater. 104–107, 817 (1992)]. Nonetheless, we report remarkable spontaneous ferromagnetism at 293 K after sintering, prominently in oxygen. This apparently introduced excess oxygen at vacant quasioctahedral sites, promoting spin-flip and ferromagnetic interchain coupling. Thermogravimetry (TGA) revealed excess oxygen, ≈0.17 O/Cu. X-ray diffraction (XRD) yielded a comparatively smaller unit cell. Ferromagnetism disappeared by oxygen depletion, mimicking reported nonmagnetism of Ca2CuO3−δ [Okuda et al. (1992)]. Elemental analysis showed insignificant magnetic impurity traces. Tc ranged between 680 K and 723 K, depending on freshness and purity. Saturation magnetization varied with processing, optimally 0.30 A · m2/kg at 1.0 T applied field. Coercivity and remanence varied with purity.
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Title: Spontaneous ferromagnetism at room temperature in oxygen-rich dicalcium cuprate Ca2CuO3+δ
Description:
Stoichiometric Ca2CuO3, having square-planar Cu-chains [C.
L.
Teske and H.
Müller-Buschbaum, Z.
Anorg.
Allg.
Chem.
379, 234 (1970); M.
Hjorth and J.
Hyldtoft, Acta Chem.
Scand.
44, 516 (1990)], is expectedly antiferromagnetic due to 1D intrachain superexchange [K.
Okuda, S.
Noguchi, K.
Konishi, H.
Deguchi, and K.
Takeda, J.
Magn.
Magn.
Mater.
104–107, 817 (1992)].
Nonetheless, we report remarkable spontaneous ferromagnetism at 293 K after sintering, prominently in oxygen.
This apparently introduced excess oxygen at vacant quasioctahedral sites, promoting spin-flip and ferromagnetic interchain coupling.
Thermogravimetry (TGA) revealed excess oxygen, ≈0.
17 O/Cu.
X-ray diffraction (XRD) yielded a comparatively smaller unit cell.
Ferromagnetism disappeared by oxygen depletion, mimicking reported nonmagnetism of Ca2CuO3−δ [Okuda et al.
(1992)].
Elemental analysis showed insignificant magnetic impurity traces.
Tc ranged between 680 K and 723 K, depending on freshness and purity.
Saturation magnetization varied with processing, optimally 0.
30 A · m2/kg at 1.
0 T applied field.
Coercivity and remanence varied with purity.
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