Size effect on multiferroic HoMn₂O₅ nanorods

The effects of size on the magnetic properties of HoMn₂O₅ nanorods were studied. Nanorods were made with five radial (〈LC〉) × axial lengths-24(7) nm × 49(19) nm, 33(14) nm × 66(25) nm, 31(9) nm × 69(25) nm, 54(13) nm × 95(27) nm, and 114(52) nm × 409(109) nm. The axial directions of the nanorod were parallel to the c-axis of the crystals. All samples crystallized with orthorhombic Pbam symmetry with no phase change between 15 and 300 K. Upon cooling, only the sample with 〈L_C〉 = 409 nm exhibited incommensurate and incommensurate-to-commensurate antiferromagnetic transitions at 43 and 38 K, respectively. No sample yielded an obvious hysteresis loop at 2 K. Measurements of magnetic susceptibility reveal that the critical range of sizes for magnetic ordering in HoMn₂O₅ is between 〈L_C〉 = 95 and 409 nm.