Vertically Aligned Single-Crystalline CoFe2O4 Nanobrush Architectures with High Magnetization and Tailored Magnetic Anisotropy.

Sai Mu,Er-Jia Guo,Michael R Fitzsimmons,Thomas O Farmer,Gyula Eres,Xiang Gao,Lisha Fan,Kai Wang,Dongkyu Lee,Matthew F Chisholm,Ho Nyung Lee,Thomas Z Ward

doi:10.3390/nano10030472

Abstract

Micrometer-tall vertically aligned single-crystalline CoFe2O4 nanobrush architectures with extraordinarily large aspect ratio have been achieved by the precise control of a kinetic and thermodynamic non-equilibrium pulsed laser epitaxy process. Direct observations by scanning transmission electron microscopy reveal that the nanobrush crystal is mostly defect-free by nature, and epitaxially connected to the substrate through a continuous 2D interface layer. In contrast, periodic dislocations and lattice defects such as anti-phase boundaries and twin boundaries are frequently observed in the 2D interface layer, suggesting that interface misfit strain relaxation under a non-equilibrium growth condition plays a critical role in the self-assembly of such artificial architectures. Magnetic property measurements have found that the nanobrushes exhibit a saturation magnetization value of 6.16 μB/f.u., which is much higher than the bulk value. The discovery not only enables insights into an effective route for fabricating unconventional high-quality nanostructures, but also demonstrates a novel magnetic architecture with potential applications in nanomagnetic devices.

Highlights

Metal oxides, complex transition metal oxides, are highly desired for their wide range of novel properties and potential applications [1]
We demonstrated the versatility of pulsed laser epitaxy (PLE) to tailor a variety of isolated vertically aligned single-crystalline nanostructures by balancing the kinetic and thermodynamic non-equilibrium PLE processes [9,10]
We demonstrate the application of the technique to the synthesis of a ternary ferrimagnetic spinel oxide, CoFe2O4 (CFO) nanobrush

Summary

Introduction

Complex transition metal oxides, are highly desired for their wide range of novel properties and potential applications [1]. We demonstrated the versatility of pulsed laser epitaxy (PLE) to tailor a variety of isolated vertically aligned single-crystalline nanostructures by balancing the kinetic and thermodynamic non-equilibrium PLE processes [9,10]. This balance provides a simple but intriguing strategy for constructing unconventional vertically aligned single-crystalline binary oxide nanostructures in terms of material diversity including CeO2, Y2O3, and TiO2 [9,10]. The nanobrushes exhibit an abnormally high saturation magnetization value of 6.16 μB/f.u., associated with a thickness-dependent magnetic anisotropy

Materials and Methods

Magnetization of the CoFe2O4 Nanobrushes

Findings

Discussion