Giant magnetic moment of oxygen-free CuNi nanoparticles.

We prepared CuNi nanoparticles by using a newly developed technique, the so-called plasma melting technique inside an oxygen-free Ar inert gas atmosphere and studied the magnetic properties. The magnetization of these nanoparticles is enormously increased over the bulk value while the size of the particle is reduced. A weak ferromagnetic behavior is observed from the magnetic hysteresis. The giant magnetic moment, which is almost inversely linear in temperature, and the weak ferromagnetic behavior support the Langevin-type superparamagnetic nature of CuNi nanoparticles. In this case, uncompensated spins on the surfaces of the particles play an important role, even though it is not enough to explain such giant magnetic moment. These properties are related to the oxygen-free nanoparticles produced by using the plasma melting technique.