Bose-Einstein Condensation of Magnons in NiCl2-4SC(NH2)2

A Bose-Einstein condensation (BEC) has been observed in magnetic insulators in the last decade. The bosons that condensed are magnons, associated with an ordered magnetic phase induced by a magnetic field. We review the experiments in the spin-gap compound NiCl2-4SC(NH2)2, in which the formation of BEC occurs by applying a magnetic field at low temperatures. This is a contribution to the celebration for the 50th anniversary of the Solid State and Low Temperature Laboratory of the University of S\~ao Paulo, where this compound was first magnetically characterized.