We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Néel temperature TN of approximately 235 K the magnetization of the CoO shell is modulated by two wave vectors, q1=(1/2 1/2 1/2)2pi/a and q2=(100)2pi/a. Oxidation affects the q1 component of the magnetization very little, but hugely enhances the q2 component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment.

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Inderhees etal Reply:In our Letter, we reported on measurements of the specific heat of two single crystals of YBa2Cu307-<5 near the superconducting transition temperature T c . We observed a deviation from the usual mean-field discontinuity, which we attributed to Gaussian thermodynamic fluctuations. For a conventional superconductor, the amplitude ratio C + IC~ would be expected to be that of an O(n) Ginzburg-Landau theory, with «=2. In this case, the amplitude ratio is a universal number, 2 allowing us to test the hypothesis that YBa2Cu3C>7-5 is a conventional superconductor. Analyzing our data as if they corresponded to an OOi) model, we found that 5.6