skip to main content


Title: Structural and magnetic properties of CoFe2O4 thin films grown on isostructural lattice-matched substrates

Epitaxial thin films of cobalt ferrite (CoFe2O4) are grown on two isostructural substrates, (001)-oriented MgGa2O4 and ZnGa2O4, using pulsed laser deposition. The substrates have a lattice mismatch of 1.26% and 0.70% with bulk CoFe2O4 (CFO) crystal. We have systematically investigated the structural and magnetic properties of the epitaxial CFO films on these substrates. X-ray diffraction and transmission electron microscopy result analysis reveal that the films deposited on spinel ZnGa2O4 are essentially free of defects and are under a small compressive strain, while films on MgGa2O4 show partial strain relaxation along with defect formation. Room temperature magnetization data indicate that CFO grown on ZnGa2O4 substrates have a bulk-like saturation magnetization of 420 emu/cc and a uniaxial substrate-induced anisotropy value of −22.9× 106 erg/cm3 with an anisotropy field as low as 60 kOe.

 
more » « less
NSF-PAR ID:
10370754
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
American Institute of Physics
Date Published:
Journal Name:
Applied Physics Letters
Volume:
121
Issue:
10
ISSN:
0003-6951
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Magnetic insulators, such as the rare‐earth iron garnets, are promising materials for energy‐efficient spintronic memory and logic devices, and their anisotropy, magnetization, and other properties can be tuned over a wide range through selection of the rare‐earth ion. Films are typically grown as epitaxial single crystals on garnet substrates, but integration of these materials with conventional electronic devices requires growth on Si. The growth, magnetic, and spin transport properties of polycrystalline films of dysprosium iron garnet (DyIG) with perpendicular magnetic anisotropy (PMA) on Si substrates and as single crystal films on garnet substrates are reported. PMA originates from magnetoelastic anisotropy and is obtained by controlling the strain state of the film through lattice mismatch or thermal expansion mismatch with the substrates. DyIG/Si exhibits large grain sizes and bulk‐like magnetization and compensation temperature. Polarized neutron reflectometry demonstrates a small interfacial nonmagnetic region near the substrate. Spin Hall magnetoresistance measurements conducted on a Pt/DyIG/Si heterostructure demonstrate a large interfacial spin mixing conductance between the Pt and DyIG comparable to other garnet/Pt heterostructures.

     
    more » « less
  2. Abstract 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 H σ , estimated from X-ray diffraction data, ranged from 2.8–7.7 kOe with the films on (100) MGO having a higher H σ 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 H 4 and the uniaxial anisotropy field H a . Values of H 4 range from −0.24 to −0.86 kOe. The uniaxial anisotropy field H a was an order of magnitude smaller than H σ and it decreased with increasing film thickness for NFO films on (100) MGO, but H a 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. 
    more » « less
  3. Epitaxial untwinned SrRuO3 thin films were grown on (110)-oriented DyScO3 substrates by molecular-beam epitaxy. We report an exceptional sample with a residual resistivity ratio (RRR), ρ [300 K]/ρ [4 K] of 205 and a ferromagnetic Curie temperature, TC, of 168.3 K. We compare the properties of this sample to other SrRuO3 films grown on DyScO3(110) with RRRs ranging from 8.8 to 205, and also compare it to the best reported bulk single crystal of SrRuO3. We determine that SrRuO3 thin films grown on DyScO3(110) have an enhanced TC as long as the RRR of the thin film is above a minimum electrical quality threshold. This RRR threshold is about 20 for SrRuO3. Films with lower RRR exhibit TCs that are significantly depressed from the intrinsic strain-enhanced value.

     
    more » « less
  4. The ability to control and manipulate magnetic anisotropy in the colossal magnetoresistive (CMR) oxide (La,Sr)MnO3 (LSMO) is critical for its implementation in magnetic memory applications. In this work, we employ the planar Hall effect (PHE) as a powerful tool to probe the magnetic anisotropy in LSMO thin films and nanostructures, where the magnetization is too small to be detected by conventional magnetometry techniques. By analyzing the angular- and magnetic field-dependences of the PHE, we deduced an in-plane biaxial magnetocrystalline anisotropy (MCA) energy of ~1.2x10^5 erg/cm^2 in LSMO thin films fully strained on (001) SrTiO3 substrates. Creating nanoscale periodic depth modulation in LSMO establishes a uniaxial anisotropy with substantially enhanced MCA energy density, which is attributed to a high strain gradient sustained in the nanostructure. The energy competition between the biaxial and uniaxial MCA leads to multi-level resistance switching behavior in properly engineered LSMO nanostructures, which can be utilized to design the switching dynamics in magnetic memory devices. Our work points to the critical role of epitaxial strain in determining the MCA in CMR oxides, and provides an effective material strategy for engineering the magnetic properties of LSMO for novel spintronic applications with high thermal stability and high density data storage. 
    more » « less
  5. Crystallographic anisotropy of the spin-dependent conductivity tensor can be exploited to generate transverse spin-polarized current in a ferromagnetic film. This ferromagnetic spin Hall effect is analogous to the spin-splitting effect in altermagnets and does not require spin-orbit coupling. First-principles screening of 41 non-cubic ferromagnets revealed that many of them, when grown as a single crystal with tilted crystallographic axes, can exhibit large spin Hall angles comparable with the best available spin-orbit-driven spin Hall sources. Macroscopic spin Hall effect is possible for uniformly magnetized ferromagnetic films grown on some low-symmetry substrates with epitaxial relations that prevent cancellation of contributions from different orientation domains. Macroscopic response is also possible for any substrate if magnetocrystalline anisotropy is strong enough to lock the magnetization to the crystallographic axes in different orientation domains. 
    more » « less