Magnetic Transition and Magnetic Entropy Change of Gd5Si1.75Ge1.75Sn0.5

Gd5Si2Ge2.2 alloy was synthesized by arcmelting and its phase components, microstructure, and especially the line features were investigated by X- ray diffraction （XRD）, scanning-electron microscope （SEM）, energy-dispersive spectroscopy （EDS）, and transmission-electron microscope （TEM）. Gd5Si2Ge2.2 consists of Gd5Si2Ge2-type and GdGe-type phases and presents eutectic characteristics. There are many regular line features on the Gd5Si2Ge2-type phase according to SEM. EDS shows that the line feature is not the Gd5 （Si,Ge）3-type phase because Gd content decreases at the line features. Two types of line features are found in the fine microstructure of Gd5Si2Ge2-type phase by TEM. Selected area diffraction （SAD） confirms that both line features are not the secondary phase or twins. There is no changes observed in the microstructure of Gd5Si2Ge2 2 from room temperature to 1400 ℃ with in situ high temperature optical microscope, therefore, it is deduced that the line features observed by SEM are formed during the solidification.

Magnetic Transition and Magnetic Entropy Change of Gd5Si1.75Ge1.75Sn0.5

Composition and electron concentration dependence of transformation temperature in Ni_(2 x y)Mn_(1-x)Ga_(1-y), Ni_(2 x)Mn_(1-x)Ga alloys with first order magnetic transition were studied. For Ni_(2 x y)Mn_(1-x)Ga_(1-y) alloys, martensitic transformation temperature T_M increases and Curie temperature T_C decreases with the increase of electron concentration e/a, they intercept at e/a=7.68. T_M and T_C decrease when continue to increase electron concentration. While for Ni_(2 x)Mn_(1-x)Ga alloys, they cross at e/a=7.635. Before their crossing, the change tendency with e/a is the same as Ni_(2 x y)Mn_(1-x)Ga_(1-y) alloys; after their crossing, both T_M and T_C increase slowly. The different relations between T_M and T_C and e/a within two NiMnGa alloys show that T_M and T_C depend not only on e/a, but also on composition.