Hong Zeng

Preparation, microstructure, and magnetic properties of bulk nanocrystalline Gd metal

Bulk nanocrystalline gadolinium metal was prepared using spark plasma sintering (SPS) and subsequent annealing process. The SPS Gd metal had a single phase with a mean grain size of about 10nm. A pressure-induced C-axis crystal texture was found in the SPS Gd sample. With the decrease of Gd grains from micrometer to nanometer range, the Curie temperature TC decreased by 10.7K and the magnetic moment per Gd atom at 5K dropped noticeably from 7.81μB to 6.31μB. These results indicate the remarkable influence of the nanostructure on the magnetism of Gd due to the finite size effect.

Magnetocaloric effect in layer structural Gd5(SixGe1−x)4∕Gd composite material

A series of layer structural composite magnetic refrigerant materials with composition of (Gd5Si2Ge2)x(Gd)y(Gd5Si1.85Ge2.15)z was synthesized via spark plasma sintering technique. The adiabatic temperature change (ΔTad) of the composites and of the three individual components was measured directly from 245to315K with a magnetic field change of 1.5T using a homemade magnetocaloric effect measuring apparatus. For all composites with different x:y:z ratios, their resultant ΔTad uniformly peaks at 246, 276, and 296K, respectively, corresponding to the magnetic transition temperature of the three components. In addition, proper x:y:z ratio can improve both the value and the constancy of ΔTad of the composite. Compared with the three components, the value of ΔTad of the composites exhibits a more constant tendency, which is more suitable for practical application in room temperature refrigeration, when compared to those of the three components.

Magnetocaloric effect in Gd5Si2Ge2/Gd composite materials

Spark plasma sintering technique has been applied to synthesize composite Gdx(Gd5Si2Ge2)1−x (x=0.3, 0.5, and 0.7) with layer structure using high-purity gadolinium (Gd) metal and Gd5Si2Ge2 alloys. The magnetocaloric effect of the composites was studied by directly measuring adiabatic temperature change (ΔTad) with a magnetic-field change of 1.5T using a homemade magnetocaloric effect measuring apparatus. With increasing x from 0.3 to 0.7, ΔTad peak temperature shifted from 286to293K and the peak values of ΔTad slowly increased from 1.6to2.0K at a magnetic-field change of 1.5T. Meanwhile, the ΔTad peak of the composite broadened as Gd content was increased. For x=0.7, the composite showed a ΔTad ranging from 1.1to2.0K at a magnetic-field change of 1.5T in a temperature range of 260–300K, which adapted to work as a room-temperature refrigerant.

Binary Gdx(Gd5Si2Ge2) 1-x (x= 0.25, 0.33, 0.5, 0.67, 0.75 ) magnetic refrigerants for room-temperature applications

In present study, spark plasma sintering (SPS) technique, an ideal technique for quick jointing different materials, has been introduced to prepare layer structural binary composite Gdx(Gd5Si2Ge2)1-x magnetic refrigerants. In spite of their excellent magneto-thermal properties, the MCE of these materials are usually pronounced only in the vicinity of the magnetic phase transition temperature and decrease remarkably at other temperature, which will not satisfy the design requirement of a magnetic refrigerator covering a large temperature span.