Competing magnetic interactions and interfacial frozen-spins in Ni-NiO core-shell nano-rods

Abstract

Synthesis and magnetic characterization of Co-NiO-Ni core-shell nanotube arrays J. Appl. Phys. 110, 073912 (2011); 10.1063/1.3646491Ni-NiO core-shell nanoclusters with cubic shape by nanocluster beam deposition Appl. Phys. Lett. 90, 043111 (2007); This paper investigates the subtle interfacial magnetism of highly-aligned, free-standing Ni-NiO core-shell rods on a Si substrate, fabricated by electroless-plating and an anodic aluminum oxide template. Transmission electron microscopy found that the NiO shell was uniformly present along the entire rod. Vertical magnetization shift, arising from opposite field cooling conditions, suggests frozen spins (FS) at the Ni-NiO interface. The FS were related to the pinning effects of the NiO on the Ni. The pinning strength depended on the NiO thickness, displaying a tunable fashion from 6 to 10 nano-meters with thermal annealing. The FS mediated the antiferromagnetic (AFM)-ferromagnetic (FM) interfacial coupling, leading to the temperature-dependent properties of the rods. FS were evident below 100 K, at which the NiO-AFM dominated the properties with a suppressed coercive field and non-saturated magnetization. At 100 K, however, the Ni-FM was superior to the NiO-AFM with a restored FM phase. Meanwhile, the interfacial magnetic frustration occurred due to the disappearance of FS. These two factors resulted in the coercivity enhancement at 100 K. The uniqueness of the structure opens opportunities to tailoring the properties of the rods by manipulating the core-shell inter-dependency, as well as inspiring further researches concerning its applications in spintronics. V C 2012 American Institute of Physics.

Template-Free Electroless Plating of Gold Nanowires: Direct Surface Functionalization with Shape-Selective Nanostructures for Electrochemical Applications

“…Although EP struggles to produce intensely roughened and nanostructured metal films, these morphologies can be realized by postsynthetic treatments, such as thermal wrinkling of underlying polymer substrates . To obtain anisotropic nanostructures of special interest (e.g., metal nanotubes, nanowires (NWs), ,, nanorods, , or networks composed thereof), EP has to be combined with templates, which mold the deposit into such special shapes. To achieve the often desired target morphology of metal NWs, EP can be guided by either solid 1D templates (such as DNA assemblies or peptide fibers) or templates enclosing 1D pores (such as the nanochannels within track-etched polymers or mesoporous silica) .…”

Strong Pinned-Spin-Mediated Memory Effect in NiO Nanoparticles

“…The observed conventional exchange bias in Ni/NiO nanoparticles has been explained in a previous report by using a core/shell model with a higher concentration of nickel vacancies residing on the surface than in the core [ 7 , 8 ]. The field-cooling hysteresis loop has also been shown to shift vertically when measured below the freezing temperature ( T f ) [ 8 ], which can be assigned as due to the interfacial frozen spins originating from the strong pinning effect between Ni and NiO [ 13 ]. A similar interfacial frozen-spin-mediated exchange bias effect has also been observed from Fe/Fe 3 O 4 core/shell and Fe 3 O 4 hollow-shell nanoparticles [ 14 , 15 ].…”

Electrochemical synthesis and magnetism of magnetic nanotubes

“…More complex studies on the temperature-dependent magnetic properties of coreshell nanotubular structures, with a FM-AFM interfacial coupling, have also been reported (Hsu et al, 2012;Proenca et al, 2013a,d). In particular, the exchange-bias coupling between FM and AFM layers is expected to occur after field-cooling the AFM material from above its Néel temperature (Nogues and Schuller, 1999;Brems et al, 2005;Ventura et al, 2008;Maurer et al, 2009;Ali et al, 2012).…”

“…In particular, the exchange-bias coupling between FM and AFM layers is expected to occur after field-cooling the AFM material from above its Néel temperature (Nogues and Schuller, 1999;Brems et al, 2005;Ventura et al, 2008;Maurer et al, 2009;Ali et al, 2012). In fact, Hsu et al (2012) measured the exchange bias effect in core-shell Ni/NiO NRs at 50 K after field cooling the samples at AE30 kOe. Their work showed that the exchange bias effect in the studied nanostructures disappears at approximately 100 K, which was attributed to the vanishing of NiO pinning on Ni, yielding magnetic frustration at the core-shell interface.…”