Critical behavior and the absence of glass state in ferromagnetic La _0.7Ca _0.3CoO ₃ nanowires

We report a systematic study of the magnetic and thermodynamic properties of uniform La _0.7Ca _0.3CoO ₃ nanowires prepared by a hydrothermal method, and compare them with the bulk counterpart. The nanowires, ∼59 nm in diameter, are single crystalline as revealed by electron microscopy. With decreasing temperature, the bulk La _0.7Ca _0.3CoO ₃ shows a ferromagnetism followed by a reentrant glass state, whereas the nanowires show only a purely ferromagnetic ground state. The thermopower and specific heat results indicate that there exist enhanced spin and/or orbital fluctuations in the nanowires that could be responsible for the absence of the glass state. Critical behavior analysis shows that the nanowires fall into a three-dimensional Heisenberg ferromagnet class.