Effect of Particle Size on the Hysteretic Behavior and Magnetocaloric Effect of La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6) Compound

Bulk Lao.sPro.sFe11.4Sil.6 compound exhibits a large magnetic-entropy change ASm of 28.1 J/（kg K） for a magnetic-field change from 0 to 1.5 T at the Curie temperature, Tc of 186 K, accompanied by a large magnetic hysteresis of 56 J/kg and a noticeable thermal hysteresis of about 1 K. If the bulk sample is ground into middle-size particles （30-60 tm）, then the thermal hysteresis is almost eliminated and the magnetic hysteresis loss is decreased by 29%, while the large ASm maintains. Especially, fine powder with an average size of 2 tm shows the same Tc as the bulk and does not lose stability. Meanwhile, a comparatively large ASm of 13.9 J/（kg K） and a hysteresis reduction of 70% are attained. The hysteresis reduction can be ascribed to the decrease of internal strains and to the improvement of heat transfer due to the increase of the ratio of the surface area to the volume.

Effect of Annealing on the Microwave-absorption Properties of Ni/Al_2O_3 Nanocomposites

Ni/Al2O3 nanocomposites were prepared by the mechanochemical synthesis method. The annealing process enlarges the grain size of both the metal Ni and insulating Al2O3 in the as-milled nanocomposite and leads to an increase of the saturation magnetization and a decrease of the surface anisotropy. An optimal reflection loss （RL） of -23 dB is obtained in the as-milled nanocomposite at 17.8 GHz for an absorber thickness of 6.6 mm. The annealed sample exhibits a RL exceeding -20 dB in the whole Ku-band for an absorber thickness of 6.6-9.7 mm with an optimal RL of -54.7 dB at 13.2 GHz for a layer thickness of 9.3 mm. The excellent microwave-absorption properties are a consequence of a proper match of the dielectric and magnetic losses.

Magnetism and Magnetocaloric Properties of Mn_3Zn_(1-x)Sn_xC and Mn_(3-x)Cr_xZnC Compounds

Upon substitution of Sn for Zn, the Curie temperature of Mn3ZnC is lowered from 380 to 375 K for MnzZno.gsSno.osC and to 305 K for Mn3Zno.75Sno.25C. In accordance with the second-order ferromagnetic-paramagnetic transition, a room-temperature magnetocaloric effect without thermal and magnetic hysteresis is observed over a wide temperature range. The maximum value of the magnetic-entropy change ABM for a magnetic-field change from 0 to 5 T is 2.42 J.kg^-1·-K^-1 at 386 K for Mn3Zno.95Sno.osC and 1.70 J·kg^-1.K^-1 at 308 K for Mn3Zn0.75Sno.25C. Meanwhile, substitution of Cr for Mn lowers the temperature of ferromagnetic-ferrimagnetic transition from 233 K for Mn3ZnC to 230 K for Mn2.9Cro.tZnC and to 175 K for Mn2.iCro.oZnC. An inverse magnetocaloric effect with △Bu equal to 0.28 J·kg^-1.K^-1 at 223 K for a field change from 0 to 1.47 T is observed for Mn2.gCro.zZnC.

Tunable quantum Shubnikov-de Hass oscillations in antiferromagnetic topological semimetal Mn-doped Cd_(3)As_(2)

Three-dimensional Dirac semimetal Cd_(3)As_(2)has been considered as an excellent candidate for applications of electronic devices owing to its ultrahigh mobility and air-stability.However,current researches are focused mainly on the use of gate-voltage to control its carrier transport tunability,while the manipulation of transport properties by element-doping is quite limited.Here we report the tunable magneto-transport properties by adjusting Mn-doping in the Cd_(3)As_(2)compound.We find that Mnelement doping has a strong influence on the Fermi level positions,and the Fermi energy approaches to Dirac point with higher Mn-doping.More importantly,the introduction of Mn atoms transforms diamagnetic Cd_(3)As_(2)to anti ferromagnetic(Cd,Mn)_(3)As_(2),which provides an approach to control topological protected Dirac materials by ma nipulating antiferro magnetic order parameters.The Shubnikov-de Hass oscillation originates from the surface states,and the Landau fan diagram yields a nontrivial Berry phase,indicating the existence of massless Dirac fermions in the(Cd_(1-x)Mn_x)_(3)AS_(2)compounds.Our present results may pave a way for further investigating anti ferromagnetic topological Dirac semimetal and expand the potential applications in optoelectronics and spintronics.

Magnetic transitions and magnetocaloric effect in MnAs_(0.9)P_(0.1)

The compound MnAs0.9P0.1 exhibits a multistep magnetic order-order transition from a helimagnetic γ-phase with Hα-type magnetic order to a ferromagnetic β-phase at 80 K and then to a helimagnetic α-phase at 203 K. The γ-β transition exhibits the characteristics of a first-order transition with a thermal hysteresis as large as 6 K, while the β-α transition is of second order with a thermal hysteresis smaller than 2 K and without magnetic hysteresis. With these two successive helimagnetism-related transitions, magnetic-entropy changes of -2.1 J/（kg·K） at 203 K for a field change from 0 to 5 T and 0.1 J/（kg·K） at 83 K for a field change from 0 to 1 T are obtained. Investigation of the magnetocaloric effect associated with a transition from Hα-type magnetic order to FM order may open a new route to explore candidates for magnetic refrigeration.