Weakly ferromagnetic microspheres bearing paramagnetic CrBO3 core and nonmagnetic polyvinylbutyral shell

A new class of core–shell microspheres was prepared through a modified solvent evaporation technique by coating chromium orthoborate (CrBO₃) particles with a commercial resin, namely Mowital®B30HH (polyvinyl butyral, PVB). Well‐shaped spherical particles were obtained in diameters ranging from 40 to 420 µm. The morphological, structural, thermal, and magnetic properties were characterized by SEM, FTIR, UV–Vis, VSM (Vibrating Sample Magnetometry), and thermal analysis techniques. Uncoated CrBO₃ is paramagnetic at room temperature and antiferromagnetic at low temperatures (T_N = 12 K) while PVB itself is nonmagnetic at room temperature. The results indicated that the microspheres having a paramagnetic core and nonmagnetic shell displayed weakly ferromagnetic properties at room temperature. The observed ferromagnetism was correlated with the particle size and higher saturation magnetization values were achieved with smaller microspheres. This unconventional magnetic behavior can be tuned by varying the particle size and may allow CrBO₃/PVB microspheres to serve as a smart material in future applications. Copyright © 2009 John Wiley & Sons, Ltd.