Structural and magnetic properties of NiFe2O4 thin films grown on isostructural lattice-matched substrates

Abstract

Nickel ferrite (NiFe2O4) thin films are grown epitaxially on two different isostructural substrates, (100)-oriented MgGa2O4 and ZnGa2O4, using pulsed laser deposition. These spinel substrates have a lattice mismatch of 0.62% and 0.04%, respectively, with NiFe2O4 crystal. While the films grown on MgGa2O4 substrates exhibit significant strain resulting in a tetragonal distortion of the crystal structure, the films on ZnGa2O4 substrate are essentially strain-free and retain their cubic structure because of the near-perfect lattice match. Magnetometry data suggest that film strain is the principal factor determining the anisotropy of these NiFe2O4 films. This is also confirmed by the effective magnetization values obtained from ferromagnetic resonance (FMR) measurements. While there is only a modest decrease in effective Gilbert damping constant with strain reduction, an enhancement in the spin voltage is observed in the spin Seebeck effect (SSE) measurements for NiFe2O4 films grown on ZnGa2O4 substrate with thickness ≤200 nm.

Strain induced anisotropy in liquid phase epitaxy grown nickel ferrite on magnesium gallate substrates

“…Ferromagnetic resonance (FMR) measurements were carried out to determine the magneto-crystalline anisotropy field H 4 and growth induced anisotropy fields H a in the films. These data indicate a switch from easy plane anisotropy field in the PLD films of thickness less than a micron 27 – 29 to a uniaxial anisotropy in the thicker LPE films. For films on (100) MGO substrates, H a decreased with increase in film thickness whereas an increase in H a with increasing thickness was measured for films on (110) MGO.…”

“…Most of the H 4 values in Table 4 are higher than the single crystal value of −0.512 Oe 21 that could be due to variations in the bond angle and bond lengths and a tetragonal distortion in the films. Thin films of NFO on MGO, ZGO, and on MgAl 2 O 4 are also reported to have H 4 = −78 Oe to −370 Oe that are smaller than the bulk single crystal values 27 , 29 . Nickel ferrite film prepared by laser molecular beam epitaxy (MBE) on (001) STO was reported to have H 4 = −0.29 kOe 43 .…”

“…It is however possible to achieve a significant modification of magnetic parameters in thin films. A variety of techniques were used in the past to synthesize films of NFO, including electrodeposition 22 , chemical vapor deposition 23 , microwave-assisted solvothermal process 24 , pulsed laser deposition (PLD) 25 – 29 , and liquid phase epitaxy (LPE) 30 , 31 . The objective in most of the past studies was to take advantage of strain due to film-substrate lattice mismatch to achieve a large growth induced anisotropy field.…”

“…The objective in most of the past studies was to take advantage of strain due to film-substrate lattice mismatch to achieve a large growth induced anisotropy field. Recent reports of significance in this regard are (i) Zn and Al substituted nickel ferrite film on MgAl 2 O 4 (MAO) substrate 26 and (ii) nickel ferrite, NiFe 2 O 4 (NFO) on MgGa 2 O 4 (MGO), CoGa 2 O 4 (CGO), and ZnGa 2 O 4 (ZGO)substrates 27 – 29 . In the case of 15–57 nm thick films of Al and Zn substituted NFO on MAO substrates, low losses characterized by ferromagnetic resonance (FMR) line-widths of 5–40 Oe for the frequency range 5–35 GHz and a strain induced anisotropy field on the order of 10 kOe were reported 26 .…”

“…In the case of 15–57 nm thick films of Al and Zn substituted NFO on MAO substrates, low losses characterized by ferromagnetic resonance (FMR) line-widths of 5–40 Oe for the frequency range 5–35 GHz and a strain induced anisotropy field on the order of 10 kOe were reported 26 . A subset of current authors investigated the magnetic characteristics of 450 nm–1 m thick NFO films prepared by pulsed laser deposition on MGO, CGO and ZGO substrates with lattice mismatch of 0.8%, 0.2%, and 0.04%,respectively 27 – 29 . Growth induced in-plane anisotropy fields as high as 11.9 kOe for films on MGO, 0.5 kOe for CGO, and 0.1 kOe for ZGO were measured.…”