Extrinsic and intrinsic magnetoresistance contributions of CrO2 thin films

Rüdiger, Ulrich; Rabe, M.; Samm, K.; Özyilmaz, Barbaros; Pommer, J.; Fraune, Michael; Güntherodt, G.; Senz, Stephan; Hesse, D.

doi:10.1063/1.1362658

Cited by 25 publications

(14 citation statements)

References 16 publications

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“…In the intermediate-field range spin-dependent scattering at loose spins in the vicinity of grain boundaries seems to be the leading source of negative MR contribution and increases with increasing temperature. The observed linear and negative MR at high temperatures can be interpreted in terms of a recently proposed double-exchange mechanism of CrO 2 [11,12,16]. The magnitude of the anisotropic MR (AMR) due to spin-orbit interaction is less than 0.1% over the whole temperature range investigated.…”

Section: Introductionmentioning

confidence: 84%

“…The magnetic saturation moment of CrO 2 is approximately 2µ B per Cr 4+ ion [15]. The ferromagnetic ordering has recently been interpreted in terms of a double-exchange mechanism [11,12,16]. For the electronic configuration one assumes one localized electron in a xy-orbital and one itinerant electron ((yz + zx)-orbital).…”

Section: General Propertiesmentioning

confidence: 99%

“…The CrO 2 films show three characteristic MR regimes [11]. At low magnetic fields (<0.1 T) and at low temperatures, intergrain tunnelling magnetoresistance (ITMR) dominates, whereas in the high-field regime ordinary Lorentz MR is the dominant contribution to the MR, which can be related to the crystalline properties (i.e.…”

Section: Introductionmentioning

confidence: 99%

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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: Introductionmentioning

confidence: 84%

Section: General Propertiesmentioning

confidence: 99%

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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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“…A scanning electron microscopy (SEM) image of (010)-oriented CrO 2 crystallites on the Cr 2 O 3 (0001) initial layer is shown in Fig. 1 1 Scanning electron microscopy image of (010)-oriented CrO 2 crystallites on a Cr 2 O 3 (0001) initial layer [10] ple has been exposed to air. No further treatment has been performed.…”

Section: Experiments and Resultsmentioning

confidence: 99%

Magnetic anisotropy of textured CrO 2 thin films investigated by X-ray magnetic circular dichroism

Goering¹,

Justen²,

Geissler³

et al. 2002

Applied Physics A: Materials Science & Processing

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Highly a-axis-textured CrO 2 films have been deposited on Al 2 O 3 (0001) substrates by chemical vapor deposition. CrO 2 has been found to have highly a-axis (010)-oriented columnar growth on a Cr 2 O 3 (0001) initial layer. The sixfold surface symmetry of the Cr 2 O 3 initial layer leads to three equivalent in-plane orientations of the a-axis-oriented CrO 2 unit cell. We report Cr L 2,3 X-ray magnetic circular dichroism data along the surface normal and at 60 • off-normal sample orientation. For a 60 • sample alignment, a strong increase of the projected orbital moment could be observed for unoccupied majority t 2g states using moment analysis. Therefore, the c axis is identified as the intrinsic magnetic easy axis of CrO 2 . In addition, a small spin moment and a very strong magnetic dipole term T z have been found. PACS 75.30.Cr; 75.30.Gw; 78.20.Lj; 78.70.Dm; 78.20.Bk IntroductionThe theoretically predicted 100% spin polarization at the Fermi energy, ε F , of CrO 2 makes it a promising material for magnetoelectronic devices [1][2][3]. According to Jullière's model, the magnetoresistance (MR) of a ferromagnet/insulator/ferromagnet tunnel junction depends on the spin polarization of the electrode material used [4]. The MR increases with increasing spin polarization of the ferromagnetic electrode material. Also, injection of spins from ferromagnetic metals into semiconductors may be allowed only for highly polarized metallic electrodes [5]. Additionally, transition-metal oxides like CrO 2 , high-temperature superconductors and colossal magnetoresistance lanthanum-based manganates have attracted a lot of theoretical interest due to the complex interplay between orbital, structural and electronic degrees of freedom. This has revived research on half-metallic ferromagnetic transitionmetal oxides, especially CrO 2 , in the past few years. Unfortunately, CrO 2 is metastable at room temperature and atmospheric conditions and typically a thin Cr 2 O 3 layer covers the CrO 2 surface. Methods like photoemission (PES), ✉ Fax: +49-711/689-1912, E-mail: goering@mf.mpg.de X-ray absorption (XAS) or X-ray magnetic circular dichroism (XMCD) spectroscopy could not easily be used for examination of basic properties of CrO 2 , because of their intrinsic surface sensitivity. Therefore, only a few experimental results on single crystals or epitaxial-grown thin films have been published. Nevertheless, spectroscopic methods are able to give quantitative information about intrinsic magnetic properties of CrO 2 . Experiment and resultsCrO 2 crystallizes in a tetragonal rutile-type structure, where chromium atoms form a body-centered tetragonal unit cell. Cr sites are octahedrally surrounded by oxygen atoms. The apical axis of the oxygen octahedra is oriented along the [110] ([110]) direction for the edge (bodycentered) Cr ions. The lattice parameters are a = b = 4.421 Å and c = 2.916 Å [6,7]. CrO 2 is a metastable Cr-oxide phase at room temperature, orders ferromagnetically at T C = 393 K and degrades above 400 K at ambient atm...

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“…32,33 More recently, a detailed MR study of epitaxial CrO 2 ͑100͒ films was performed between 4.2 and 300 K in magnetic fields up to 23 T reporting three characteristic MR regimes. 30,31 At low magnetic field ͑Ͻ0.1 T͒ and at low temperatures ͑4.2 K͒, intergrain tunneling MR ͑ITMR͒ dominates, whereas in the high-field regime ordinary Lorentz force MR is reported to be the dominant contribution to the MR. In the intermediate-field range, spindependent scattering at weakly bound spins in the vicinity of grain boundaries seems to be the leading source of negative MR contribution showing a linear increase with increasing temperature.…”

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confidence: 99%

Micromagnetism and magnetotransport properties of micron-sized epitaxialCrO2(100)wires

et al. 2007

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We report a detailed study of the magnetic domain configurations and the magnetization reversal in epitaxial CrO 2 ͑100͒ wires ͑0.5-5 m widths͒ patterned along different crystallographic directions. Magnetic force microscopy imaging in zero field reveals single domain states for wires fabricated along the magnetic easy axis, while wires perpendicular to the magnetic easy axis exhibit a stripe domain configuration. The behavior in an applied field and the switching of the magnetization is probed by magnetoresistance ͑MR͒ measurements. Depending on the orientation of the wire with respect to the easy and hard magnetocrystalline anisotropy axes and the field direction, distinctly different reversal modes are observed including inhomogeneous magnetization configurations. These modes and configurations can be explained taking into account the interplay between the different anisotropy terms. MR measurements at variable temperatures demonstrate that the low temperature MR response is dominated by intergrain-tunneling magnetoresistance, while at elevated temperatures it is superseded by the anisotropic MR.

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Extrinsic and intrinsic magnetoresistance contributions of CrO2 thin films

Cited by 25 publications

References 16 publications

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Growth and magnetotransport study of thin ferromagnetic CrO₂films

Magnetic anisotropy of textured CrO 2 thin films investigated by X-ray magnetic circular dichroism

Micromagnetism and magnetotransport properties of micron-sized epitaxialCrO2(100)wires

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Extrinsic and intrinsic magnetoresistance contributions of CrO2 thin films

Cited by 25 publications

References 16 publications

Growth and magnetotransport study of thin ferromagnetic CrO2films

Growth and magnetotransport study of thin ferromagnetic CrO2films

Magnetic anisotropy of textured CrO 2 thin films investigated by X-ray magnetic circular dichroism

Micromagnetism and magnetotransport properties of micron-sized epitaxialCrO2(100)wires

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Growth and magnetotransport study of thin ferromagnetic CrO₂films

Growth and magnetotransport study of thin ferromagnetic CrO₂films