  A silicon micromechanical torsional oscillator is used to measure the
hysteresis loops of two manganite La_0.67Ca_0.33MnO_3 nanotubes at different
temperatures, applying an external field along its main axes. These structures
are composed of nanograins with a ferromagnetic core surrounded by a dead
layer. Micromagnetic calculations based on the stochastic
Landau-Lifshitz-Gilbert equation, are performed to validate a simple model that
allows for quantitatively describing the ferromagnetic behavior of the system.
Further simulations are used to analyze the experimental data more in depth and
to calculate the coercive field, the saturation and remanent magnetizations,
and the effective magnetic volume for single nanotubes, over a wide temperature
range.
