Ferromagnetic Multipods Fabricated by Solution Phase Synthesis and Hydrogen Reduction

Abstract

A simple approach combining pyrolysis and hydrogen reduction is formulated for making ferromagnetic-branched nanostructures called Co multipods. The CoO multipods (branched nanostructures) were produced through the pyrolysis of cobalt-oleate in octadecane at 280 C with the presence of oleic acid under the protection of pure nitrogen. The angles between the nearest arms are 90 . After the reduction of the branched CoO nanostructures in flowing hydrogen gas in a tubular oven at 290 C, the CoO is reduced to pure cobalt with hexagonal crystal structure and the branched shapes are retained. Anisotropic magnetic properties were found for cobalt multipods on silicon substrates.

Origin of antiferromagnetism in CoO: A density functional theory study

“…Using GGA+ U, we find the calculated lattice constant a for the ZB structures is 4.61 Å, in good agreement with experimental values of 4.55 Å. 24 For the ZB phase calculated at a = 4.61 Å, the electronic configuration of the occupied states can be written as ͓͑e g ↑͒ 2 ͑t 2g ↑͒ 3 ͑e g ↓͒ 2 ͔. This also leads to a magnetic moment close to 3 B per Co. We find that, unlike the RS phase, in the ZB phase the AFM states always have lower energy than the FM state.…”

“…To test the validity of our calculation, we have also studied the stability of CoO in the ZB phase. It has been shown experimentally that metastable ZB CoO with space group F43m can be formed, 24 in which the Co 2+ ion ͑d 7 ͒ is in a tetrahedral ͑T d ͒ environment. Under the T d crystal field, the Co 3d states split into lower e g and upper t 2g states, opposite to the order in the RS structure.…”

Unravelling the Elusive Antiferromagnetic Order in Wurtzite and Zinc Blende CoO Polymorph Nanoparticles

“…The latter can be found in highly defected rock salt‐CoO, as possible defected structures in nonstoichiometric rock‐salt crystals or as a by‐product in Li–Co oxide batteries . Moreover, zinc blende‐CoO has been used as seed for the growth of rock salt‐CoO and Co multipods and exhibits appealing semiconducting properties . However, very little is known about the magnetism of zinc blende‐CoO .…”

“…Moreover, zinc blende‐CoO has been used as seed for the growth of rock salt‐CoO and Co multipods and exhibits appealing semiconducting properties . However, very little is known about the magnetism of zinc blende‐CoO . Although its magnetic properties have not been elucidated experimentally, theoretical studies predict an antiferromagnetic order .…”

“…[9] However, very little is known about the magnetism of zinc blende-CoO. [4][5][6][7][8][9][10][11][12] Although its magnetic properties have not been elucidated experimentally, theoretical studies predict an antiferromagnetic order. [13,14] Concerning wurtzite-CoO, more systematic studies have only recently been carried out.…”