Theory of the thermomagnetic effects in thin films in a magnetic field of arbitrary magnitude

Askerov, B. M.; Kuliev, B. I.; Figarova, S. R.; Shteinshraiber, V. Ya.

doi:10.1002/pssb.2220860111

Cited by 4 publications

(4 citation statements)

References 4 publications

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“…The presence of this negative MR contribution over the whole temperature range and in all three field geometries is at variance with a previous interpretation, where a finite-size effect in the presence of a magnetic field has been employed to explain the decrease of resistivity in the intermediate-field range at low temperatures [20]. Such a negative MR is expected in ferromagnetic systems when the mean free path of the charge carriers is of the same order of magnitude as the structure size [45]. This mechanism should strongly depend on the field orientation and the sample geometry, which have not been observed for the microfabricated samples.…”

Section: Magnetic and Magnetotransport Propertiessupporting

confidence: 70%

“…Such a negative MR is expected in ferromagnetic systems when the mean free path of the charge carriers is of the same order of magnitude as the structure size [45]. This mechanism should strongly depend on the field orientation and the sample geometry, which have not been observed for the microfabricated samples.…”

Section: Magnetic and Magnetotransport Propertiesmentioning

confidence: 92%

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Growth and magnetotransport study of thin ferromagnetic CrO₂films

Rabe

Pommer

Samm

et al. 2001

J. Phys.: Condens. Matter

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Highly a-axis-textured CrO 2 films have been deposited on Al 2 O 3 (0001) and on isostructural TiO 2 (100) substrates by a chemical vapour deposition technique. For Al 2 O 3 substrates a columnar growth of CrO 2 (010) on an initial Cr 2 O 3 (0001) layer has been found in transmission electron microscopy as well as in x-ray diffraction investigations. The sixfold in-plane symmetry of a (0001)-oriented Cr 2 O 3 initial layer leads to three equivalent in-plane orientations of the CrO 2 unit cell as confirmed by electron diffraction and scanning electron microscopy. The growth can be understood by a simple model of the in-plane symmetries of the Al 2 O 3 (0001), Cr 2 O 3 (0001), and CrO 2 (010) lattices. The growth on TiO 2 (100) substrates leads to (100)-oriented CrO 2 films of higher crystalline quality than the ones grown on Al 2 O 3 (0001). Transmission electron microscope images show growth of CrO 2 (100) directly on the TiO 2 (100) substrates and no significant Cr 2 O 3 inclusions within the CrO 2 (100) layer. All contributions to the magnetoresistance (MR) due to anisotropic MR, Lorentz MR, spin disorder, and intergrain tunnelling MR have been determined and partly correlated with the crystalline properties of the samples investigated. For films of both types the intrinsic linear contribution to the high-field MR does not depend on the crystalline quality of the films and supports the suggested intrinsic doubleexchange mechanism for CrO 2 .

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Section: Magnetic and Magnetotransport Propertiessupporting

confidence: 70%

Section: Magnetic and Magnetotransport Propertiesmentioning

confidence: 92%

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Rabe

Pommer

Samm

et al. 2001

J. Phys.: Condens. Matter

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“…Therefore the negative MR decreases with increasing temperature and only the intrinsic positive MR remains at room temperature. It is noteworthy that negative transverse MR is also expected in ferromagnetic systems when the mean free path of the charge carriers is of the same order of magnitude as the structure size . Since the diameter of the nanorod is about 75 nm and the mean free path in CrO 2 is as large as 70 nm at 5 K, this size effect is expected at low temperature.…”

mentioning

confidence: 92%

“…It is noteworthy that negative transverse MR is also expected in ferromagnetic systems when the mean free path of the charge carriers is of the same order of magnitude as the structure size. 42 Since the diameter of the nanorod is about 75 nm and the mean free path in CrO 2 is as large as 70 nm at 5 K, 5 this size effect is expected at low temperature. This could be another possible mechanism contributing to the negative MR observed in our devices.…”

mentioning

confidence: 99%

Spin-Dependent Tunneling Transport into CrO₂ Nanorod Devices with Nonmagnetic Contacts

2008

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Single-crystal nanorods of half-metallic chromium dioxide (CrO2) were synthesized and structurally characterized. Spin-dependent electrical transport was investigated in individual CrO2 nanorod devices contacted with nonmagnetic metallic electrodes. Negative magnetoresistance (MR) was observed at low temperatures due to the spin-dependent direct tunneling through the contact barrier and the high spin polarization in the half-metallic nanorods. The magnitude of this negative magnetoresistance decreases with increasing bias voltage and temperature due to spin-independent inelastic hopping through the barrier, and a small positive magnetoresistance was found at room temperature. It is believed that the contact barrier and the surface state of the nanorods have great influence on the spin-dependent transport limiting the magnitude of MR effect in this first attempt at spin filter devices of CrO2 nanorods with nonmagnetic contacts.

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Electron Transport Phenomena in Conductive Films

Askerov¹,

Kuliev²,

Figarova³

1984

Physica Status Solidi (b)

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liitroductionThe extensive use of thin filnis in modern techniques as well as the observation of new physical phenomena due to the finite size of the specimens have led to their active investigation in recent years [1 to 101. These new phenomena may be used as a source of additional inforination on the basic physical properties of crystals: structures of energy bands, mechanisms of bulk and surface scattering of charge carriers, etc. The concept of a "thin film" means that the thickness of the fihn is comparable with a length characteristic of some phenomenon. The efiects met with in films may be divided into two groups -the quantum and classical size effects. Quantum size effects take place when the sample dimensions become of the order of the de Uroglie wavelength of a typical charge carrier [9, 101. Classical size-dependent effects occur in a sample when a t least one of the lengths characterizing the motion of charge carriers becomes of the order of the film thickness or of the characteristic length of the potential variation near the surface (the Debye length). Examples of such lengths are the mean free path, the cooling length, bipolar diffusion length, intcrvalleyscattering length, etc. Which particular size effect is to be observed depends upon which of these parameters becomcs comparable with the specimen thickness.The present review deals with a theoretical study of the influence of size cffects upon the charge carrier mean frcc path. I n othcr words, we are intcrestcd in the influence of surface scattering upon the transport phenomena in semiconductive filnis.Size-dependent effects associated with the mean free path have been studied for many years. The first consistent theory of the conductivity in filnis was suggestctl by Fuchs [ l l ] on the basis of a frce electron gas niodel under the assumption of a spherical Fcrmi surface. The surface scattering was takeii into account by using the due boundary conditions for the distribution function. The boundary conditions to be attachecl to the noltzmann equation constitute the central point in the study of the mean free path size cffects; they contain all the information concerning the surface and are in a scnse similar to the collision integral of the bulk scattering problem. The Fuchs boundary conditions are phenomenological and disregard the details of the surface structure. A rigorous formulation of the boundary conditions based upon thc general concepts of the theory of electron surface scattering as well as their application to specific situations and energy band structures were discussed comprehensively in other reviews L12, 131.Sondheimer [14] extended the Fuchs theory to the galvanomagnetic effects in a transverse magnetic field; he was the first to predict the resistance oscillations in a magnetic field. The studies carried out by Fuchs and Sondheimer wcre generalized to the case of scattering by two film surfaccs with different spccularities in [15, 161.The E'uchs theory was generalized as well to take account of the spccific structure of energy ...

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Theory of the thermomagnetic effects in thin films in a magnetic field of arbitrary magnitude

Cited by 4 publications

References 4 publications

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Spin-Dependent Tunneling Transport into CrO₂ Nanorod Devices with Nonmagnetic Contacts

Electron Transport Phenomena in Conductive Films

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Theory of the thermomagnetic effects in thin films in a magnetic field of arbitrary magnitude

Cited by 4 publications

References 4 publications

Growth and magnetotransport study of thin ferromagnetic CrO2films

Growth and magnetotransport study of thin ferromagnetic CrO2films

Spin-Dependent Tunneling Transport into CrO2 Nanorod Devices with Nonmagnetic Contacts

Electron Transport Phenomena in Conductive Films

Contact Info

Product

Resources

About

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Spin-Dependent Tunneling Transport into CrO₂ Nanorod Devices with Nonmagnetic Contacts