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•Fracture behaviour of BaTiO3 thin film attached to different substrates were studied using microcantilever facture experiments.•These experiments revealed a significant effect of the ...substrate elastic modulus on the fracture toughness of the films.•Increase in fracture toughness of the bi-layered system was found as the crack tip approach the film-substrate interface.•Presence of ductile interface shielded the crack tip and changed the crack trajectory.•These measurements provide a template for design of thin films with increased fracture resistance.
Damage tolerance of a thin film attached to a substrate is dependent on several parameters such as film thickness, film orientation, residual stresses, nature of interfaces, microstructure and defects present. Here we study the fracture resistance and crack growth trajectory in BaTiO3 thin films attached to elasticially stiff substrates using micromechanical experiments and finite element modeling. Microcantilever fracture tests are carried out on bi-layered systems of BaTiO3 film on Pt-Si and SrTiO3 substrates to study the effect of interfaces, texture and elastic mismatch on fracture toughness. The substrates in the bi-layers are chosen to force the crack to experience a shielding effect in terms of a decrease in the crack driving force. Experiments revealed an unexpectedly large increase in fracture toughness when the crack tip is closer to a stiffer substrate, qualitatively matching the predictions from the numerical model. The bi-layered films attached to the substrate showed 125% (on Pt-Si) and 160% (on SrTiO3) increase in fracture toughness compared to the free-standing films, for the first time, revealing the significant effect of elastic modulus of the substrate on improving the fracture resistance at such micrometer length scales.
•Preparation of bilayer of CoFe2O4/ZnFe2O4 on quartz substrate which results in large magnetization after annealing.•The obtained room temperature magnetization is higher than any binary ferrite and ...is close to metallic Nickel.•The highest magnetic moment value cannot be explained by Néel model.
In this paper, we report our observation of an extraordinarily large value of magnetization in an annealed CoFe2O4/ZnFe2O4 bilayer. Sets of bilayers of CoFe2O4/ZnFe2O4 were deposited at ambient temperature, using pulsed laser deposition setup equipped with Nd: YAG laser, and subsequently annealed in air at different temperatures for 2 h. The highest attained value of magnetization was ≈7200 G at 300 K and ≈15000 G at 10 K for a bilayer with a 60 nm thickness tCo of CoFe2O4 and 40 nm thickness tZn of ZnFe2O4, annealed at 650 °C. This measured magnetization value is the highest for any oxide spinel reported thus far in the literature. The observed value is close to that of metallic Ni and cannot be explained by current theories of magnetism in oxides.
Engineering magnetic materials into a thin film form while preserving its excellent magnetocaloric response is essential in the development of miniature magnetic coolers. We demonstrate how this can ...be achieved in the case of EuTiO3 – an emerging multiferroic material. Unlike conventional cases where reduced dimensionality considerably decreased the magnetic entropy change (ΔSM) and hence the refrigerant capacity (RC), we show the large low-field enhancements of ΔSM and RC in a ∼100 nm thick nanocrystalline EuTiO3 film (ΔSM ∼ 24 J kg−1K−1 and RC = 152 J kg-1 for μ0ΔH = 2 T) relative to its single crystal counterpart (ΔSM ∼ 17 J kg−1K−1 and RC ∼ 107 J kg-1 for μ0ΔH = 2 T). The nanocrystalline EuTiO3 film is an excellent candidate for cryogenic magnetic refrigeration. From our study, a new approach for improving both MCE and RC in magnetic nanomaterials is proposed, which will stimulate further research on magnetocaloric thin films and related cooling devices.
•Engineering magnetocaloric materials on the nanometer scale is essential in the development of miniature magnetic coolers.•We demonstrate how this can be achieved in the case of EuTiO3 – an emerging multiferroic material.•We show the large enhancements of both ∆SM and RC upon applied moderate field changes (< 2T) in a nanocrystalline EuTiO3 film.•Our study shows the important roles of strain and reduced dimensionality in enhancing the magnetocaloric figures-of-merit.
This study investigates the temperature-dependent quasi-static magnetoelectric (ME) response (αE) of electrically poled lead-free Na
0.4
K
0.1
Bi
0.5
TiO
3
–NiFe
2
O
4
(NKBT–NFO)-laminated ...composites. The aim is to understand the temperature stability of ME-based sensors and devices. The relaxor ferroelectric nature of NKBT is confirmed through impedance and polarization–electric (PE) hysteresis loop studies, with a depolarization temperature (
T
d
) of approximately 110 °C. Heating causes a decrease and disappearance of planar electromechanical coupling (
K
p
), charge coefficient (
d
31
), and remnant polarization (
P
r
) above
T
d
. The temperature rise to 125 °C also leads to a reduction in magnetostriction (
λ
) and magnetostriction coefficient (
q
= d
λ
/d
H
) of NFO by approximately 33% and 25%, respectively. At room temperature, the bilayer and trilayer configurations exhibit maximum ME responses of approximately 33 mV/cm·Oe and 80 mV/cm·Oe, respectively, under low magnetic field conditions (
H
∼ 300–450 Oe). The ME response of NKBT/NFO is highly sensitive to temperature, decreasing with heating in accordance with the individual temperature-dependent properties of NKBT and NFO. This study demonstrates a temperature window for the effective utilization of NKBT/NFO-based laminated composite ME devices.
MnFe2O4 thin films were pulsed laser deposited on to quartz substrate from room temperature (RT) to 650 °C in a pure argon environment. Temperature dependence of spontaneous magnetization (4πMS) was ...measured on these films from 10 K to 350 K using a vibrating sample magnetometer. Ferromagnetic resonance (FMR) study was also carried out at 300 K. The exchange stiffness constant (D) values were obtained by fitting the 4πMS data to the Bloch’s equation. The D values of the films thus found decreases while the 4πMS value increases, though non-monotonically, with the increase in TS and tend to reach bulk values at TS = 650 °C. The variation in D and 4πMS values of the films are explained based on the degree of inversion and oxidation state of cations in thin films.
Zinc ferrite films were deposited on fused quartz substrate at different substrate temperatures using a pulsed laser deposition technique. The deposited samples were ex situ annealed at different ...temperatures up to 650 °C in air for 2 h. It was found that the spontaneous magnetization of the films depends both on the grain size and on the substrate temperatures. The largest values of spontaneous magnetization for our sample were 3000 G at 300 K and 6600 G at 10 K, for the film deposited at substrate temperature of 450 °C. The ferromagnetic resonance linewidths of the films were found to depend both on substrate and annealing temperatures. A relatively low linewidth of 195 Oe was observed in parallel configuration for the film deposited at 250 °C and annealed at 350 °C.
Nano-sized magnesium ferrite particles were prepared by sol gel combustion synthesis and were either furnace cooled or quenched after calcining at various temperatures ranging from 300 to 800°C. A ...magnetisation value of 61emu/g was obtained at 5K for sample calcined at 800°C and quenched in liquid nitrogen temperature. This is one of the highest reported values of magnetisation obtained from quenching at such a lower temperature. An estimate of the number of Fe3+ ions on A and B sites was made after applying Néel Model on the magnetisation values measured at 5K. It was estimated that Fe3+ ions segregates out from both sites disproportionately so as to cause a net decrease in the overall moment. The resultant cation distribution is found to be consistent with the coercivity data.
•Highest magnetisation (M) among nano sized magnesium ferrite particles was obtained.•The obtained magnetisation was nearly double of furnace cooled bulk sample.•Coercivity (Hc) is anti correlated to M for samples with different heat treatment.•Coefficient of non saturation of magnetisation in M–H loop (a), is correlated with Hc.•Hc, M and a are explained in terms of cation distribution obtained using NNéel model.
Single phase nano-crystalline zinc ferrite (ZnFe2O4) thin films were deposited on fused quartz substrate using the pulsed laser deposition technique. The films were deposited at different substrate ...temperatures. The field dependence of magnetization at 10 K shows hysteresis loops for all the samples. Temperature dependence of the field cooled (FC) and zero field cooled (ZFC) magnetization indicated irreversible behavior between the FC and ZFC data, and the irreversibility depends on the measuring magnetic field. The thermo-magnetic irreversibility in the magnetization data is correlated with the magnitude of the applied field and the coercivity (HC) obtained from the M-H loops.
Y 3 Fe 5 O 12 thin films with thickness 10 nm ≤ t ≤ 1440 nm were grown on Gd 3 Ga 5 O 12 (111) substrates by pulsed laser deposition. The X-ray diffraction experiments confirmed the films are pure ...yttrium iron garnet (YIG) phase with preferred (111) orientation. The magnetic and microwave properties were studied as a function of film thickness by the dc magnetization and ferromagnetic resonance (FMR) measurements. The FMR linewidth (ΔH) was found to decrease with the increase in film thickness (10 nm ≤ t ≤ 45 nm), attaining a minimum value of ΔH ⊥ = 5 Oe and ΔH || = 6 Oe, for perpendicular and parallel resonance, and then rising with further increase in thickness. Acid etching experiments were performed to understand the mechanism contributing to ΔH. The increase in ΔH with thickness (t > 45 nm) may be explained in terms of extrinsic mechanisms, such as inhomogeneities present at the surface of the films. However, the decrease in ΔH with thickness (t <; 45 nm) is believed to be due to the surface anisotropy effect. The films showed low coercivity values in the range of ~1.5-7 Oe, which is an indicator of good quality YIG films.
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