Study On Structure And Magnetic Correlation Properties Of ?Nd,Dy,Ho?Co₂ Related Compounds

In this paper,the structure and magnetic correlation properties of?Nd,Dy,Ho?Co₂related compounds were studied.Nd Co_2-xMn_x?Dy Co_2-xGe_x?Dy Co_2-xCr_xand Ho Co₂B_xcompounds were prepared by arc melting.The crystal structure were characterized and analyzed by XRD and Fullprof,and the magnetic properties were tested by PPMS.The wave absorbing properties of Dy Co₂and Ho Co₂compounds were tested by HP8722ES microwave vector network analyzer.The XRD results show that Nd Co_2-xMn_x?x=0.0-0.5?compounds have a good single-phase structure,and their lattice constant cell volume and the curie temperature?T_C?gradually increase with the increase of x content.The T_Cincreased from 102 K?x=0.0?to202 K?x=0.5?,further approaching room temperature.All the compounds are second-order phase transition materials.Although the magnetic entropy change??S_M?of Nd Co_2-xMn_xcompounds decreases with the increase of Mn composition,their operating temperature range are wider than that of Nd Co₂compounds,so their relative cooling capacity?RCP?are larger than that of Nd Co₂compound.Because Mn is cheaper and Nd Co_2-xMn_xcompounds have higher T_Cand RCP values,they have potential research value in the field of magnetic refrigeration technology.XRD data show that Ge and Cr can only be dissolved in a small amount of Dy Co₂compound.With the increase of Ge content,the T_Cof Dy Co_2-xGe_xcompounds increased from 151 K?x=0.0?to 179 K?x=0.2?.The replacement of Cr had little effect on T_C,but compared with Dy Co₂,the T_Cvalue of Dy Co_2-xCr_xcompounds were reduced.The hysteresis loop at 10 K indicates that both Dy Co_2-xGe_xand Dy Co_2-xCr_xcompounds have a certain degree of coercivity?H_C?,which increases linearly with the increase of x content.Arrott curves show that both Dy Co_2-xGe_xand Dy Co_2-xCr_xhave undergone the transition from first-order phase transition to second-order phase transition.It is worth mentioning that the Dy Co_1.95Ge_0.05compound still maintained the characteristics of first-order phase transition when x=0.05.Although,they had lower?S_Mvalue,but they have wide working range,which have great RCP value also have the potential research value in the field of magnetic refrigeration.Studied on Ho Co₂B_x?x=0.0-0.2?compounds shown that interstitial atoms B can only be doped into the Ho Co₂compound in trace amounts.The isothermal magnetization curves of Ho Co₂B_xcompounds are shown the shape of S near T_C,indicating that they have undergone the transformation from paramagnetism to ferromagnetism under the induction of magnetic field.All compounds still maintained the characteristics of first order phase transition.Ho Co₂B_xcompounds still have a large?S_Mafter B doping.Under the magnetic field of 1 T,the?S_Mof Ho Co₂B_x?x=0.0-0.15?compounds ware 12.9,12.58,10.11 and8.07 J/kg.K,respectively.It shows that Ho Co₂B_xhave potential prospect in the application of low field magnetic refrigeration technology.The minimum reflectivity of both Dy Co₂and Ho Co₂compounds are less than-10d B?the absorption rate is more than 90%?,the minimum reflectivity of Dy Co₂compound is-18.7d B?the absorption rate is 98.6%?and the minimum reflectivity of Ho Co₂compound is-29d B?the absorption rate is 99.8%?.Both Dy Co₂and Ho Co₂compounds have certain bandwidth effects and may have potential research value in absorbing materials.