General synthesis of rare-earth orthochromites with quasi-hollow nanostructures and their magnetic properties

Rare-earth orthochromites are extremely interesting because of their potential applications as multifunctional materials. However, it is still a great challenge for the general synthesis of nanostructured full rare-earth orthochromites series. Here, a facile and versatile solvothermal reduction strategy is successfully employed in the preparation of rare-earth chromites with quasi-hollow nanostructures. X-ray diffraction data show that all the products have the orthorhombic perovskite structure. The electron microscopy analysis reveals that the morphology of the product is seriously affected by the rare-earth ionic radius. Tube-like and vesicle-like structures can be formed for the larger and smaller rare-earth cationic radii, respectively. The experimental results suggest that the room-temperature precursors of potassium rare-earth chromates serve as a self-template for the in situ reduction and formation of rare-earth orthochromites hollow structures. The magnetization studies demonstrate that all the products, as it would be expected, undergo a magnetic transition from paramagnetic to antiferromagnetic phase at the Neel temperature (T-N1) attributed to Cr3+-Cr3+ exchange and this critical temperature goes up linearly with an increase in the rare-earth ionic radius. Additionally, some samples exhibit a variety of fancy magnetic properties, including thermal hysteresis suggesting a first-order magnetic transition, magnetization reversal due to the antiparallel polarization of the R3+ paramagnetic moments by the Cr3+ canted antiferromagnetic ones, and magnetic exchange bias related to the spin reorientation transition of the Cr3+ magnetic moments.