One-step room-temperature synthesis of nanocrystallme Mn3O4 hausmannite, without heating posttreatment, was carried out from a simple dissolution of manganese(II) acetate in a Mixture of N,N'-dimethylformamide (DMF) and water. Homogeneous nanocrystals like rods were obtained, with an average width and length of 6.6 +/- 1.2 nm and 17.4 +/- 4.1 nm, respectively, and a preferential growth along the [001] direction. Magnetization measurements on a powdered sample showed ferrimagnetic behavior at low temperatures. Under zero-field cooling (ZFC) measurement at 100 Oe, the observed blocking temperature (T-B) was 37 K. 41 (c) 2005 Elsevier Inc. All rights reserved.