Zhou et al. Nanoscale Research Letters 2011, 6:276 http://www.nanoscalereslett.com/content/6/1/276 Page 4 of 6 Figure 3 The characterization of the Co/InP nanocomposite structure: (a) EDS spectrum and (b) XRD pattern. strong ferromagnetism of Co. In a word, the magnetism of such Co/InP magnetic semiconductor nanocomposite is completely determined by the deposition time of Co. The exhibited ferromagnetism under the room tempera- ture, originating from the Co particles embedded in the n-type porous InP matrix, is different from that of the superparamagnetism of Co particles in Cu and dendrimer matrix [22,36]. Figure 5 shows magnetic hysteresis loops of Co/InP composite structure with the deposition time of 5 min for both perpendicular and parallel orientations, where H// and H⊥ represent the field applied perpendicular and parallel to the surface of the InP template, respectively. Typical coercivities with Hc⊥ = 775 Oe and Hc// = 644 Oe are clearly found in the inset of Figure 5, indicating the enhanced coercivity compared with that of the bulk Co (10 Oe). The relatively larger coercivity in perpendi- cular orientation suggests weak anisotropy of the system, i.e., magnetization easy axis is perpendicular to the surface of InP template. This magnetic anisotropy of the system is determined by the relatively strong-shape ani- sotropy of Co nanoparticle arrays embedded in the por- ous InP matrix compared with the magnetocrystalline anisotropy of hexagonal Co particle. Furthermore, both magnetization curves for perpendicular and parallel are sheared as shown in Figure 5, indicating the existence of inter-particle interactions, which is also manifested by the low squareness ratios, (Mr/Ms)⊥ = 0.34 and (Mr/Ms)// = 0.36. Similar sheared hysteresis loops were also found in Co/ZrO2, Co/AAO, and Ni/AAO nanocomposite materials [2,14,17]. In brief, magnetic anisotropy in the Co/InP nanocomposite structure with easy axis perpendi- cular to the surface of InP matrix is compatible with that of typical magnetic nanostructures such as nanowires and nanotubes [8,14,16,20,21,29], i.e., the magnetization easy axis is along the long axis of nanostructures, which is the result of the competition between the dominant shape anisotropy and magnetocrystalline anisotropy. Figure 4 Field-dependent magnetization curves (M-H) of the Co/InP nanocomposite structure, where the magnetic field is applied perpendicular to the surface of the InP template with different deposition times of Co: (a) 30 s (square) and 90 s (solid line), (b) 5 min (square), the inset shows the magnetization curve of the n-type porous InP template (square).