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Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes.

ABSTRACT: Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al₂O₃ substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetism and magnetostriction) and strain gradients (flexomagnetism).

SUBMITTER: Du D

PROVIDER: S-EPMC8093223 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes.

Du Dongxue D Manzo Sebastian S Zhang Chenyu C Saraswat Vivek V Genser Konrad T KT Rabe Karin M KM Voyles Paul M PM Arnold Michael S MS Kawasaki Jason K JK

Nature communications 20210503 1

Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al<sub>2</sub>O<sub>3</sub> substrates. Despite the presence of the graphene interlayer, the ...[more]

PMID: 33941781

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Project description:This work focuses on the nature of magnetic anisotropy in 2.5-16 micron thick films of nickel ferrite (NFO) grown by liquid phase epitaxy (LPE). The technique, ideal for rapid growth of epitaxial oxide films, was utilized for films on (100) and (110) substrates of magnesium gallate (MGO). The motivation was to investigate the dependence of the growth induced anisotropy field on film thickness since submicron films of NFO were reported to show a very high anisotropy. The films grown at 850-875 C and subsequently annealed at 1000 C were found to be epitaxial, with the out-of-plane lattice constant showing unanticipated decrease with increasing film thickness and the estimated in-plane lattice constant increasing with the film thickness. The uniaxial anisotropy field Hσ, estimated from X-ray diffraction data, ranged from 2.8-7.7 kOe with the films on (100) MGO having a higher Hσ value than for the films on (110) MGO. Ferromagnetic resonance (FMR) measurements for in-plane and out-of-plane static magnetic field were utilized to determine both the magnetocrystalline the anisotropy field H4 and the uniaxial anisotropy field Ha. Values of H4 range from -0.24 to -0.86 kOe. The uniaxial anisotropy field Ha was an order of magnitude smaller than Hσ and it decreased with increasing film thickness for NFO films on (100) MGO, but Ha increased with film thickness for films on (110) MGO substrates. These observations indicate that the origin of the induced anisotropy could be attributed to several factors including (i) strain due to mismatch in the film-substrate lattice constants, (ii) possible variations in the bond lengths and bond angles in NFO during the growth process, and (iii) the strain arising from mismatch in the thermal expansion coefficients of the film and the substrate due to the high growth and annealing temperatures involved in the LPE technique. The LPE films of NFO on MGO substrates studied in this work are of interest for use in high frequency devices.

Dataset Information

Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes.

Publications

Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes.

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