The temperature dependence of the dc magnetization and the specific heat capacity are systematically investigated for the perovskite YbCrO3 chromites. The results show that there exist two complex sequences of magnetic transitions with the characteristics of magnetization reversal and Yb3+/Cr3+ spin ordering at different temperature, respectively. The antiferromagneticlike transition around TN=118 K is attributed to the antiferromagnetic ordering of the Cr3+ spins and a negative magnetization, accompanied with a tendency to the plateau below 10 K caused by the Yb3+ ordering. We obtain the Weiss constant of −197.0 K and an effective moment of 5.99μB for the sum of the free ion values of 4.53μB for Yb3+ and 3.87μB for high-spin Cr3+ from the experiments, which shows an antiferromagnetic interaction and the existence of weak canted antiferromagnetic (CAFM) characteristics. Corresponding to the magnetic phase transition in the Cr sublattice, the specific heat capacity under zero fields exhibits a sharp λ-shape peak near temperature TN, which is depressed and broadened smoothly with the increase in the magnetic field. And a shoulder-shaped Schottky-type anomaly below 12 K is observed in the specific heat capacity curves. This can be interpreted by accounting for the molecular field approximation by assuming that the induced polarization of the paramagnetic ytterbium ions is opposite to the ferromagnetic moment of the chromium ions. According to the results of the zero fields cooling and the field cooling magnetization, the possible existence of spin ordering for the Yb3+ moments can be predicted.

A novel cold-seeding approach of top-seeded melt growth of RE-Ba-Cu-O bulk was studied by employing a MgO crystal seed and a buffer pellet. The growth process is divided into two steps. The MgO seed is used to texture-grow the small RE-Ba-Cu-O pellet with high melting point (T p ) and the textured pellet induces the texture growth of the bulk at lower temperature. Undercooling and RE211 content of the pellet are adjusted to avoid the misorientation caused by lattice mismatch between MgO and the RE-Ba-Cu-O matrix. Bulk samples prepared with this method show good growth sections and superconducting performance. One of the promising advantages of this method is to process high T p RE-Ba-Cu-O bulks with a cold-seeding method, for example Nd-Ba-Cu-O bulk.

The seeded infiltration and growth of Gd-Ba-Cu-O single grains using a YBa 2 Cu 3 O y pressed pellet as the liquid source has successfully solved the liquid source leakage problem even at T max ∼ 1100 • C. As a development of this process, a simple but essential modification to insert a liquid source pellet at the bottom of the pre-form was made to the top-seeded melt growth process. The present method resulted in a significant enhancement of the trapped flux density of the Gd-Ba-Cu-O grains. In the growth kinetics, we interpreted that the enriched liquid source surrounding the growth front leads to a more uniform distribution of Gd 2 BaCuO 5 in the matrix and an enlarged c-orientation growth area, which help suppress the formation of high angle grain boundaries. Furthermore, we demonstrated that the present method is of great advantage in multi-seeded processes.

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