Anisotropic magnetization and dynamic susceptibility sign change in single-crystalNa0.85CoO2

Abstract

The DC and AC magnetic susceptibilities of Na0.85CoO2 single crystals were measured for the different crystal orientations of H (ab)-and H (c)-axis. The DC-magnetic susceptibility for H (c)-direction exhibited the antiferromagnetic transition at TN = 22 K. The thermal hysteresis between the zero-field-cooled (ZFC) and the field-cooled (FC) magnetization below TN and the large frustration parameter indicated the spin frustration along the c-axis. For an applied magnetic field in H (ab)-plane, the DC magnetic susceptibility exhibited the logarithmic divergent behavior at low temperatures (T ≤ 6.8 K). This could be understood by the impurity spin effect, dressed by the spin fluctuation. From the AC magnetic susceptibility measurements, the real part of the AC-susceptibility for H (ab) exhibited the spin glass-like behavior at low temperatures (T ≤ 4 K). Remarkably, for an applied AC magnetic field with H (c)-axis, the sign of the AC magnetic susceptibility changed from a positive to a negative value with increasing AC magnetic field frequency (f ≥ 3 kHz) at low temperatures (T ≤ 7 K). We interpret the sign change of AC magnetic susceptibility along the c-axis in terms of the sudden sign reversal of the phase difference φ from in-phase to out-of-phase response with an applied AC magnetic field in the AC-susceptibility phase space.

Crystal electric field ofP2-NaxCoO2for the intermediate spin state of CoShu1, Chou2 2013Phys. Rev. B

“…However, it is clear that except for the sample of x=0.71, the µ ef f per Co 4+ values are progressively and significantly higher than 1.732 µ B for x > 0.71, as indicated in Table I. Similar results have also been reported consistently in all early published works, 6,[13][14][15] including for Li x CoO 2 , which has a similar CoO 2 2D triangular lattice. 4 While a Na content higher than ∼0.71 is expected to contain a lower level of Co 4+ and less doped itinerant holes, the increasing Curie constant remains unclear.…”

Ferrimagnetic ordering and spin entropy of field-dependent intermediate spins inNa0.82CoO2

“…[18,19] However, FM-like behavior with different onsets near 8, 22, and 29 K has also been observed, with strong cooling rate and history dependence. [3,20,23,24] In addition, the staging effect for Na-layers with different stack orderings was found to be consistent with the highly sensitive thermal and field history dependence for x between ∼0.71-0.86. [3] We have examined the fitting of Weiss temperature (Θ) from the PM-state spin susceptibility data obtained in fields from zero to 7 Tesla, [17,25] and the Θ values were found to be persistently negative and nearly independent of the field.…”

Coexistence of ferromagnetism and unconventional spin-glass freezing in the site-disordered kagome ferrite SrSn2Fe4O11

“…85 CoO 2 cobaltate[45], and in the BiFeO 3 ferrite, where it was attributed to a modulated magnetic structure[38]. Such a sign change has not been reported previously for RTF materials; verification/clarification of this phenomenon will require more detailed magnetothermal measurements at variable frequency.To clarify the low-temperature dynamics of the spin glass state of SrFe 2 Sn 4 O 11 , we first applied a simple Arrhenius law to describe the frequency dependence of T p ≡ T f , as has been done for conventional spin glasses composed of isolated clusters (superparamagnets), where f = f 0 exp (-E a /k B T f ) (Here, E a and f 0 are the energy barrier and characteristic frequency of a superparamagnet, respectively.…”