Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

Yinqing, Zhou; Jin, Xuesong; Shvets, I. V.

doi:10.1063/1.1687632

Cited by 36 publications

(41 citation statements)

References 10 publications

(9 reference statements)

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“…6,11 Therefore, a change in the strain state does not appear to be responsible for the anomaly properties as all the films are equally strained. The dead layer formed by Mg diffusion between the MgO substrate and the magnetite films and also the dead layer on the top uncapped film are considered as the possible reasons for the anomalies in resistivity and magnetic properties of the ultrathin films.…”

Section: Resultsmentioning

confidence: 99%

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The magnetic and magnetoresistance properties of ultrathin magnetite films grown on MgO substrate

Yinqing

McEvoy

Ramos

et al. 2006

Journal of Applied Physics

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We report on the properties of ultrathin ͑2, 4, 6, and 8 nm͒ epitaxial films of magnetite, Fe 3 O 4 , grown on MgO ͑100͒. Atomic force microscopy image and V-I curves suggest that the films at this thickness are still continuous. The resistivity versus temperature results imply that the conductivity mechanism in all these films is similar. The resistivity of 4 nm thick film is much greater than that of 6 and 8 nm films. The films show ferrimagnetic instead of reported superparamagnetic behavior. The dead layer formed by Mg diffusion between MgO substrate and magnetite films and also the dead layer on the top uncapped film could be the possible reasons for the anomalous resistivity and magnetic properties of the ultrathin films. The effect of the "dead layer" in the thinner film is relatively greater than the one in the thicker film and should lead to a lower magnetoresistance.

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Section: Resultsmentioning

confidence: 99%

“…Other details of the film growth are presented in Ref. 6. Growth mode and crystalline quality of the films were monitored in situ by reflection high-energy electron diffraction ͑RHEED͒.…”

Section: Methodsmentioning

confidence: 99%

The magnetic and magnetoresistance properties of ultrathin magnetite films grown on MgO substrate

Yinqing

McEvoy

Ramos

et al. 2006

Journal of Applied Physics

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“…The details of the growth process are given elsewhere. 20 Reflection high-energy electron diffraction ͑STAIB Instruments͒ was used to determine the growth mode and growth rate ͑0.3 Å / s͒ of the films. In order to avoid the effect of sample quality variation, we cut two well characterized 70 nm thin films of size 10 mmϫ 10 mm into four pieces each of 5 mmϫ 5 mm size.…”

Section: Methodsmentioning

confidence: 99%

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Kumar

Khan

Srivastava

et al. 2006

Journal of Applied Physics

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The effect of swift heavy ion ͑SHI͒ irradiation ͑190 MeV Ag͒ on structural, electrical transport and magnetic properties of epitaxial magnetite ͑Fe 3 O 4 ͒ thin films ͑thickness ϳ70 nm͒ grown on MgO͗100͘ oriented substrate have been investigated. The x-ray diffraction shows that at low fluence values up to 5 ϫ 10 11 ions/ cm 2 , the strain in the films is relaxed, whereas, at higher fluence range 1 ϫ 10 12 -1 ϫ 10 13 ions/ cm 2 , the epitaxial relationship with the substrate is lost along with a phase transformation from magnetite to more oxidized magnetite phase ͑i.e., maghemite͒. The Verwey transition temperature measured by electrical transport is found to increase from 109 to 117 K with the low fluence SHI irradiation, which is related to the irradiation induced strain relaxation and structural modifications. At higher fluences the system did not show Verwey transition and the resistance is also increased. The similar results were obtained by magnetization studies. The observed magnetization at 1 T field is increased at low fluence suggesting the reduction of areas with frustrated exchange interactions associated with the cationic arrangement at the anti phase boundaries. At higher fluences it decreases monotonically, indicating the emergence of other phases. The observed modifications are explained on the basis of structural strain and disorder induced by swift heavy ions, which lead to modification of the interionic Coulomb potential at octahedral sublattices and bandwidth in this system.

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“…We apply this fabrication process to examine the electronic properties of thin (40-60 nm) single-crystal magnetite films grown on MgO substrates [19]. Magnetite undergoes a first-order phase transition when cooled through ∼122 K, known as the Verwey temperature, T V , with a structural deformation accompanied by a drastic decrease in electrical conductivity [24].…”

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“…1. Starting substrates were either silicon wafers with 200 nm thermally grown SiO 2 layer, or 40-60 nm thick magnetite films on MgO substrates [19]. Poly-(methylmethacrylate) (2% in chlorobenzene) was spin-coated at 3000 rpm on the wafers to form a 500 nm resist layer, followed by baking at 180 • C for 2 min.…”

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Nanogaps with very large aspect ratios for electrical measurements

Fursina

Lee

Sofin

et al. 2008

Applied Physics Letters

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For nanoscale electrical characterization and device fabrication it is often desirable to fabricate planar metal electrodes separated by large aspect ratio gaps with interelectrode distances well below 100 nm. We demonstrate a self-aligned process to accomplish this goal using a thin Cr film as a sacrificial etch layer. The resulting gaps can be as small as 10 nm and have aspect ratios exceeding 1000, with excellent interelectrode isolation. Such Ti/Au electrodes are demonstrated on Si substrates and are used to examine a voltage-driven transition in magnetite nanostructures. This shows the utility of this fabrication approach even with relatively reactive substrates.PACS numbers: 81.07. -b,81.16.-c,85.35.-p There is much interest in the electronic characterization of nanoscale materials and the creation of working molecular-based devices [1]. Both goals demand the fabrication of metallic electrodes separated by a distance comparable with the targeted length, i.e. a few nanometers. Much recent progress has been made in nanogap fabrication, and several techniques were proposed, including electromigration [2,3,4], electrodeposition [5,6], mechanically controlled break junctions [7], advanced ebeam lithography methods [8,9,10,11,12], on-wire lithography [13], etc. Interelectrode distances down to 1-2 nm may be achieved [4,6,9] by some of these methods, though without much control of gap aspect ratio.A significant challenge is fabricating two electrodes separated by a nanometer gap running parallel over a macroscopic width (high-aspect-ratio (HAR) nanogaps). HAR nanogap fabrication has been demonstrated based on a selective etching of cleaved GaAs/AlGaAs heterostructures [14,15]. However, this method requires particular substrates and allows only restricted gap geometries. A much simpler technique was proposed recently [16] with potentially no limitations on the width of the gap. Two separate lithographic patterning steps are used to define first and second electrodes, while the interelectrode separation is controlled by the oxidation of an Al sacrificial layer deposited upon the first electrode. The native aluminum oxide layer, Al 2 O 3 , overhangs the underlying metal and serves as a mask during the deposition of the second electrode. This layer must be removed afterwards, but since Al 2 O 3 , corundum, is one of the most chemically inert materials [17], removal by direct chemical etching is very difficult. In a refinement, the authors deposited an additional sacrificial layer of SiO 2 and subsequently used etchant for SiO 2 to remove the SiO 2 and Al/Al 2 O 3 layers [16]. The use of SiO 2 etchant greatly limits the use of this approach in conjunction with conventional silicon electronics. While this method potentially allows fabrication of HAR nanogaps, the reported aspect ratios are less than 10 [16].In this letter we report a highly reproducible and flexible method for nanometer-sized (10-20 nm) gap fabrication with aspect ratios exceeding 1000. Modifying the original method [16] by replacing the Al layer wi...

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Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

Cited by 36 publications

References 10 publications

The magnetic and magnetoresistance properties of ultrathin magnetite films grown on MgO substrate

The magnetic and magnetoresistance properties of ultrathin magnetite films grown on MgO substrate

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Nanogaps with very large aspect ratios for electrical measurements

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