Nanoscale magnetization inhomogeneity within single phase nanopillars

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Nanoscale magnetization inhomogeneity within single phase nanopillars

Thomas O. Farmer, Er-Jia Guo, Ryan D. Desautels, Lisa DeBeer-Schmitt, Aiping Chen, Zhongchang Wang, Quanxi Jia, Julie A. Borchers, Dustin A. Gilbert, Ben Holladay, Sunil K. Sinha, and Michael R. Fitzsimmons

Phys. Rev. Materials 3, 081401(R) – Published 1 August 2019

Abstract

We report observation of a radial dependence in the magnetic anisotropy of epitaxially strained $CoF e_{2} O_{4}$ nanopillars in a $BaTi O_{3}$ matrix. This archetypal example of a multiferroic heterostructure with a self-assembling three-dimensional architecture possesses significant out-of-plane uniaxial magnetic anisotropy. The anisotropy originates from the large magnetostriction of $CoF e_{2} O_{4}$ and the state of stress within the nanocomposite. Magnetometry suggests the existence of two magnetic phases with different anisotropies. Micromagnetic simulations of a core-shell magnetic anisotropy qualitatively reproduce features of the magnetic hysteresis and elucidate the magnetization reversal mechanism: The magnetization initially reorients within the pillar core, followed by that of the shell. This is consistent with polarized small-angle neutron scattering which can be described by a $CoF e_{2} O_{4}$ magnetization that is nonuniform on nanometer length scales. As the length scale of inhomogeneity of the magnetic anisotropy is similar to estimates of the relaxation of the displacement field from the $CoF e_{2} O_{4} - BaTi O_{3}$ interface, stress and its influence on structure provide an important route to new functionality of vertically aligned nanopillars for applications in low-power memory, computing, and sensing.

Received 26 September 2018

DOI:https://doi.org/10.1103/PhysRevMaterials.3.081401

Physics Subject Headings (PhySH)

Ferroelectric domains Magnetic domains Magnetic susceptibility Magnetic texture

Multiferroics Nanostructures

Micromagnetic modeling Small angle neutron scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Thomas O. Farmer^1,2,*, Er-Jia Guo^1,3, Ryan D. Desautels^1,4, Lisa DeBeer-Schmitt¹, Aiping Chen⁵, Zhongchang Wang⁶, Quanxi Jia^7,8, Julie A. Borchers⁹, Dustin A. Gilbert^9,10, Ben Holladay¹¹, Sunil K. Sinha¹¹, and Michael R. Fitzsimmons^1,12,†

¹Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
²ISIS Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom
³Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
⁴Seagate Technology, 1 Disc Drive, Derry, BT48 0BF, United Kingdom
⁵Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁶Department of Quantum and Energy Materials, International Iberian Nanotechnology Laboratory, Braga 4715-330, Portugal
⁷Department of Materials Design and Innovation, University at Buffalo, Buffalo, New York 14260-5030, USA
⁸Department of Physics, Konkuk University, Seoul, 05029, Republic of Korea
⁹NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
¹⁰Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37919, USA
¹¹Department of Physics, University of California, San Diego, La Jolla, California 92093-0319, USA
¹²Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA