We report the effect of iron vacancies on the magnetic property of spin and charge ordered system YbFe 2 O 4 single crystals. The excess amount of iron compensates for the evaporation of iron during crystal growth. We concluded that samples grown with the standard method contain iron vacancies of more than 10%. It is considered that increasing the iron in the starting material recovers the iron stoichiometry, and the proper magnetic property appears. With recovery of the chemical stoichiometry, the magnetic hysteresis loop changes from a double loop to a single loop, which indicates the development of spin coherence and the appearance of a large ferrimagnetic domain. The anomaly found in the thermomagnetization curve at approximately 150 K, the so-called T LT transition, disappears with better stoichiometry. This fact indicates that T LT is not a kind of phase transition but an effect of iron vacancy. Our discovery demonstrates that most of the crystals used in RFe 2 O 4 research might contain many iron vacancies. The confused discussions on this material about the spin order model, the charge order model, and so on might reconsider such chemical stoichiometry, including iron vacancies.
Alkali superoxide CsO 2 is one of candidates for the spin-1 2 one-dimensional (1D) antiferromagnet, which may be sequentially caused by an ordering of the π-orbital of O − 2 molecule below T S ∼ 70 K. Here, we report on the magnetism in powder CsO 2 and high-magnetic field magnetization measurements in pulsed-magnetic fields of up to 60 T. We obtained the low temperature phase diagram around the antiferromagnetic ordering temperature T N = 9.6 K under the magnetic field. At 1.3 K, remarkable up-turn curvature in the magnetization around a saturation field of ∼ 60 T is found, indicating the low-dimensional nature of the spin system. The saturated magnetization is also estimated to be ∼ 1µ B , which corresponds to the spin-1 2 . We will compare it with the theoretical calculation.
Polycrystalline rubidium superoxide (RbO2) has been synthesized by using solution method followed by the reaction process under the cooling condition of-40 °C. X-ray Powder Diffraction (XRD) spectra showed that RbO2 was successfully synthesized by this method. The magnetic susceptibility and pulsed muon spin relaxation (μSR) measurements were carried out in order to study the magnetic properties of RbO2.
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