K.W. Zhou

Study on stability of RECo5 phases (RE=Dy, Gd)

Abstract The eutectoid decomposition reaction that occurred in RECo5 phases (RE=Dy and Gd) at low temperature was discussed and confirmed by X-ray powder diffraction (XRD), differential thermal analysis, and scanning electron microscopy. The decomposition temperature of the GdCo5 and DyCo5 were identified as 805.8 and 900 °C, respectively. The GdCo5 and DyCo5 phases could not be found in the isothermal section of Gd-Dy-Co ternary system at 800 K. Reasons for the absence of the RE2Co7 phase in the XRD patterns were discussed in detail.

Influence of Carbon on the Giant Magnetocaloric Effect of LaFe11.7Si1.3

The influences of carbon on phase formation, Curie temperature, and magnetic entropy change of the NaZn13-type LaFe11.7Si1.3 were investigated. Seven carbon-containing alloys, LaFe11.7Si1.3C(subscript x) with x=0, 0.03, 0.06, 0.10, 0.20, 0.30, and 0.50, respectively, were prepared for this investigation. Experimental results show that addition of a small amount of carbon in LaFe11.7Si1.3 is favorable for the formation of the NaZn13-type structure of LaFe11.7Si1.3C(subscript x). The lattice constant increases with C addition and x increases in the alloy because of the introduction of C as interstitial atoms. The Curie temperature of LaFe11.7Si1.3C(subscript x) increases from 194 K to 225 K as x increases from 0 to 0.5. Large magnetic entropy changes were observed in these carbon-containing alloys LaFe11.7Si1.3C(subscript x) because of their first-order structural/magnetic transition. The maximum magnetic entropy change of 27.5 J•kg^(-1)•K^(-1) at 202 K for the 0-1.56 T magnetic field change was observed in the alloy with x=0.06. The large magnetic-entropy changes corresponding to low magnetic field change, and the low cost of the material of LaFe11.7Si1.3C(subscript x) makes it a promising candidate to be used as magnetic refrigerants in the corresponding temperature range.

Structure and Magnetocaloric Effect in Tb(Co1-xSnx)2 Alloys

Abstract The phases and magnetocaloric effect in the alloys Tb(Co 1- x Sn x ) 2 with x = 0, 0.025, 0.050, 0.075, 0.100 were investigated by X-ray diffraction analysis and magnetization measurement. The substitution of Sn in TbCo 2 was limited. The cubic MgCu 2 -type structure for the sample of TbCo 2 was confirmed by the results of X-ray powder diffraction and the rest samples consist of the TbCo 2 phase mainly, together with some TbCo 3 and Tb 5 Sn 3 impurity phases. The impurity phases increase with the increase of Sn contents. The magnetic phase transition in all samples keeps second-order transition. T C increases slightly by Sn substitution from 230 K of the alloy with x = 0 to 233 K of the alloy with x =0.050 and then a slight decrease for higher concentration of x . The maximum magnetic entropy change in the samples Tb (Co 1- x Sn x ) 2 with x = 0, 0.025, 0.050, 0.075 are 3.44, 2.29, 1.64, 1.16 J·kg −1 ·K −1 , respectively, with the applied field change from 0 to 2.0 T.

Phase structure and magnetocaloric effect of (Tb1–xDyx)Co2 alloys

Abstract Phase structure and magnetocaloric effect of (Tb 1– x Dy x )Co 2 alloys with x =0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu 2 -type structure; with the increase of Dy content, T C decreased from 240 K (TbCo 2 ) to 130 K (DyCo 2 ), and the maximum magnetic entropy change |Δ S M,max | increased from 3.133 to 8.176 J/kg·K under low magnetic field of 0–2 T. The Arrott plot and the change of |Δ S M,max | showed that magnetic phase transition from second order to first order occured with the increase of Dy content between x =0.6 and 0.8.