  We report macroscopic magnetic measurements carried out in order to detect
and characterize field-induced quantum entanglement in low dimensional spin
systems. We analyze the pyroborate MgMnB_2O_5 and the and the warwickite
MgTiOBO_3, systems with spin 5/2 and 1/2 respectively. By using the magnetic
susceptibility as an entanglement witness we are able to quantify entanglement
as a function of temperature and magnetic field. In addition, we experimentally
distinguish for the first time a random singlet phase from a Griffiths phase.
This analysis opens the possibility of a more detailed characterization of low
dimensional materials.
