Effect of Size on Magnetic Properties of ${\hbox {NdMn}}_2{\hbox {O}}_5$ Nanorods

The effects of size on the magnetic properties of NdMn₂O₅ nanorods were studied by X-ray diffractometry, transmission electron microscopy, and measurements of magnetic susceptibility and hysteresis. Five types of nanorods with different axial lengths (〈L_C〉)×diameters(〈L_D〉)-68(36) nm×31(14) nm, 78(30) nm×33(8) nm, 95(36) nm×40(12) nm, 122(48) nm×54(16) nm, 249(46) nm×142(36) nm were made. The axial directions of the five types of nanorod were parallel to the c axis of the crystal. No particular radial direction is found. All samples crystallize with orthorhombic Pbam symmetry. Upon cooling, only the sample with 〈L_C〉 = 249 nm occurs in ferrimagnetic and antiferromagnetic ordering at 80 K and 9 K, respectively. Hysteresis testing reveals a ferrimagnetic domain between 10 K and 50 K only in the 〈L_C〉 = 249 nm sample. These tests reveal that the magnetic critical size of NdMn₂O₅ is between 〈L_C〉 = 249 nm and 122 nm. For memory storage applications, the estimated maximal capacity of NdMn₂O₅ nanorods as upstanding pillars is about 32 Gbit/in².