ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Recent magnetic studies of polycrystalline CoCl2⋅H2O showed an antiferromagnetic ordering transition at TN∼14 K and an apparent spin glass transition at ∼7 K. We now have extended the magnetic susceptibility measurements up to 300 K. The results above TN can be well described if the lowest electronic states of Co2+ in this salt are two Kramers doublets separated by ΔE/k=230 K, and if a predominantly ferromagnetic mean field interaction is introduced. The heat capacity of CoCl2⋅H2O over the range 0.6–80 K has also been measured. Below ∼10 K, Cp≈aT−2+bT3. The first term is the hyperfine contribution of the 59Co2+ nuclei. The second is the sum of lattice vibrational and electronic spin parts. Cp exhibits a λ-type peak at TN1=15.0±0.05 K, and a second λ anomaly of comparable size at TN2=13.9±0.05 K, which appears to be associated with a spin reorientation transition. Correcting the observed Cp data for the nuclear spin contribution, one may calculate the sum of lattice vibration and electron spin entropies, and thus obtain at TN1 an upper limit to the critical magnetic entropy. This amounts to 0.38 R ln 2, suggesting that a substantial part of the spin ordering in this system is of short-range and lower dimensionality. Cp also exhibits an inflection point near 4.5 K, where an unusual feature in the temperature dependence of the spin glass thermoremanent magnetization was found.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.355678
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