W.Q. Zou

Ferromagnetism in Tb doped ZnO nanocrystalline films

Nanocrystalline Tb-doped ZnO films have been prepared by ion-beam sputtering technique. Magnetic characterization showed that the films are ferromagnetic with Curie temperature (TC) higher than room temperature. By further treated with a rapid thermal annealing process, both the grain size and the carrier concentration of the films increase, while the saturation magnetization of the films decreases. This magnetic behavior can be hardly explained by either bound magnetic polaron model or free carrier mediation model, thus suggests that the grain boundaries play a key role for the origin of ferromagnetism in these films.

Effects of annealing and hydrogenation on the properties of ZnMnO polycrystalline films synthesized by plasma enhanced chemical vapour deposition

For the Mn-doped ZnO polycrystalline films fabricated with plasma enhanced chemical vapour deposition technique followed by thermal treatment at 600 °C for 5 h, the effects on both rapid thermal annealing up to 900 °C in Nitrogen ambient for 2 min and hydrogenation processing have been investigated. It has been indicated that after the rapid thermal annealing the magnetization of the films decreases. The magnetization of the films has been found to increase with the increase in hydrogenation processing duration at the early stage of the processing and gets a saturated value after about 60 min while there is a decrease with increasing electron concentration after a rapid thermal process in nitrogen ambient.

CoMnSb: A magnetocaloric material with a large low-field magnetic entropy change at intermediate temperature

A large magnetocaloric effect (MCE) has been achieved in a rare-earth-free CoMnSb alloy at low magnetic field and intermediate temperature. It is interesting to note that a relatively large magnetic entropy change ∣ΔSM∣ of 2.06J∕kgK with ΔH=0.9T was obtained around 471K. Arrott plots at various temperatures reveal that a second order magnetic transformation occurs near the Curie temperature. The origin of the large ΔSM under the conditions of intermediate temperature and low field is attributed to the magnetic transition from ferromagnetic to paramagnetic. These results suggest that CoMnSb alloy is a good candidate for large MCE when being utilized in intermediate temperature refrigeration systems for some special cases. This investigation demonstrates that some transition metal alloys with large magnetic moments may exhibit large MCE, which extends the region for exploring useful MCE materials.

Giant low-field magnetic entropy changes in Ni45Mn44?xCrxSn11 ferromagnetic shape memory alloys

A series of Ni45Mn44−xCrxSn11 (x = 0, 1, 2) ferromagnetic shape memory alloys were prepared. With slight doping of Cr, the martensitic transition temperatures decrease rapidly. The magnetic entropy changes at a low magnetic field were investigated in these alloys. The maximum value of ΔSM is 23.4 J kg−1 K−1, which was observed in Ni45Mn43CrSn11 alloys. The origin of the magnetic entropy changes in these alloys has been discussed. The giant low-field magnetic entropy changes and low cost make Ni45Mn44−xCrxSn11 alloys a promising candidate for magnetic refrigeration.