Enhanced magnetocaloric effect at quantum level crossing for a spin-gapped system

Recent studies dealing with magnetocaloric response of antiferromagnetic (AFM) spin systems have established that being superior coolants they have the potential to replace the paramagnetic salts, which are presently abundant in cooling technology. Presently we report an enhanced magnetocaloric effect (MCE) in one such spin system: NH_{4}CuPO_{4}.H_{2}O (NCP), an AFM spin 1/2 dimer. Experimental magnetization and specific heat data have been presented and these data have been employed to evaluate entropy, magnetic energy and magnetocaloric properties. We witness a sign change in magnetic Gruneisen parameter across the level-crossing field B_{C}. An efficient adiabatic cooling is observed at low temperature by tracing the isentropic curves in temperature-magnetic field plane. Energy-level crossover characteristics in NCP interpreted through MCE analysis are well consistent with the observations made from magnetization and specific heat data.