Anomalous magnetic properties of 7 nm single-crystal Co3O4 nanowires

We present a study of magnetic properties of single-crystal Co3O4 nanowires with diameter about 7 nm. The nanowires expose (111) planes composed of plenty of Co3+ cations and exhibit two order temperatures at 56K (T-N of wire cores) and 73K (order temperature of wire shells), which are far above T-N = 40K of bulk Co3O4. This novel behavior is attributed to symmetry breaking of surface Co3+ cations and magnetic proximity effect. The nanowire shells show macroscopic residual magnetic moments. Cooling in a magnetic field, a fraction of the residual moments are tightly pinned to the antiferromagnetic lattice, which results in an obvious horizontal and vertical shift of hysteresis loop. Our experiment demonstrates that the exchange bias field H-E and the pinned magnetic moments M-pin follow a simple expression H-E = aM(pin) with a a constant. (C) 2012 American Institute of Physics. [doi:10.1063/1.3674317]http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000299127200063&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Physics, AppliedSCI(E)EI8ARTICLE1null11