Nanocrystals of gadolinium orthoferrite (GdFeO₃) with morphology close to isometric and superparamagnetic behavior were successfully synthesized using direct, reverse and microreactor co-precipitation of gadolinium and iron(III) hydroxides with their subsequent heat treatment in the air. The obtained samples were investigated by PXRD, FTIR, low-temperature nitrogen adsorption-desorption measurements, HRTEM, SAED, DRS and vibration magnetometry. According to the X-ray diffraction patterns, the GdFeO₃ nanocrystals obtained using direct co-precipitation have the smallest average size, while the GdFeO₃ nanocrystals obtained using reverse and microreactor co-precipitation have approximately the same average size. It was shown that the characteristic particle size values are much larger than the corresponding values of the average crystallite size, which indicates the aggregation of the obtained GdFeO₃ nanocrystals. The GdFeO₃ nanocrystals obtained using direct co-precipitation aggregate more than the GdFeO₃ nanocrystals obtained using reverse co-precipitation, which, in turn, tend to aggregate more strongly than the GdFeO₃ nanocrystals obtained using microreactor co-precipitation. The bandgap of the obtained GdFeO₃ nanocrystals decreases with decreasing crystallite size, which is apparently due to their aggregation. The colloidal solutions of the obtained GdFeO₃ nanocrystals with different concentrations were investigated by ¹H NMR to measure the T₁ and T₂ relaxation times. Based on the obtained r₂/r₁ ratios, the GdFeO₃ nanocrystals obtained using microreactor, direct and reverse co-precipitation may be classified as T₁, T₂ and T₁–T₂ dual-modal MRI contrast agents, respectively.

The sample of GdFeO₃ nanoparticles obtained by ultrasound-assisted co-precipitation synthesis may be classified as a T₁-contrast agent for MRI at 0.47 and 1.5 T, as a T₁–T₂ dual-modal contrast agent at 3 T and as a T₂-contrast agent at 4.7 T.