Low-field magnetoresistive properties of polycrystalline and epitaxial perovskite manganite films

Li, X. W.; Gupta, AK; Xiao, Gang; Gong, G. Q.

doi:10.1063/1.119747

Cited by 372 publications

(212 citation statements)

References 14 publications

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“…Figure 3 This sharp drop is absent in single crystals and epitaxial thin films 1,2,6 and is therefore associated with the grain boundaries in polycrystalline samples. At high field, the slope of this curve becomes almost linear.…”

Section: Resultsmentioning

confidence: 99%

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Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHox
Raychaudhuri
¹
,
Sheshadri
²
,
Taneja
³

et al. 1999
Phys. Rev. B

124

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Abstract:The magnetoresistance (MR) in polycrystalline colossal magnetoresistive compounds follows a behavior different from single crystals below the ferromagnetic transition temperature. This difference is usually attributed to spin polarized tunneling at the grain boundaries of the polycrystalline sample. Here we derive a theoretical expression for the contribution of spin polarized tunneling to the magnetoresistance in ferromagnetic systems under the mean field approximation. We apply this model to our experimental data on the half metallic ferromagnet La 0.7 Sr 0.3 MnO 3 , and find that the theoretical predictions agree quite well with the observed dependence of the spin polarized MR on the spontaneous magnetization.

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Section: Resultsmentioning

confidence: 99%

“…Many of these materials (e.g., La 0.7 Sr 0.3 MnO 3 , CrO 2 , Fe 3 O 4 ) in the polycrystalline form, are now known to exhibit large magnetoresistance at low fields below the ferromagnetic transition temperature (T c ). 1,2,3,4 . Under similar conditions, magnetoresistance in single crystals is either very low or totally absent.…”

Section: Introductionmentioning

confidence: 99%

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHox
Raychaudhuri
¹
,
Sheshadri
²
,
Taneja
³

et al. 1999
Phys. Rev. B

124

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show abstract

“…Although it is now generally accepted that LFMR is a grain boundary-related feature, the underlying physical mechanisms are still under debate. In a recent paper, Gupta and Sun 26 review the three main models: the spin-polarized tunneling ͑SPT͒ of charge carriers, 27 the spin-dependent scattering of polarized electrons, 28,29 and the mesoscopic model of Evetts et al 18 This latter model supposes that the grain boundary region is polarized by adjacent magnetically soft grains and seems to be appropriate in our case, since the temperature dependence of H* suggests that the saturation field H* is directly related to the demagnetizing field. As the applied field is increased from zero to H*, the ferromagnetic domains become progressively aligned and finally the bulk magnetization reaches the saturation value.…”

Section: R"h… Curves At Several Temperaturesmentioning

confidence: 99%

Magnetotransport properties of a single grain boundary in a bulk La–Ca–Mn–O material

Vertruyen

Cloots

Rulmont

et al. 2001

Journal of Applied Physics

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Besides the ''intrinsic'' colossal magnetoresistance effect observed in single crystals, the polycrystalline manganate compounds also exhibit an ''extrinsic'' magnetoresistance related to the presence of grain boundaries. We report electrical transport and magnetic measurements carried out on a bigrain sample extracted from a floating zone method-grown rod of calcium doped lanthanum manganate. Electrical resistance was measured both within a grain and across the grain boundary, between 20 and 300 K and from 0 to 8 T. Magnetoresistance values up to 99% are reached within the grain. The temperature dependence of the resistance across the grain boundary displays a ''foot-like'' feature towards the bottom of the transition. Low field and high field magnetoresistance effects are examined. We compare our results for a ''bulk'' grain boundary to those obtained by other authors for bicrystal thin films and bulk polycrystalline materials.

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“…Recent experiments on epitaxial manganite films with a single grain boundary have allowed the high-field, colossal magnetoresistance to be separated from the low-field effect due to heterogeneous magnetization distribution in adjacent grains [8,9]. A characteristic but unexplained feature of the low-field magnetoresistance in manganite ceramics [10], polycrystalline films [11,12], and tunnel junctions [13,14] is its rapid decay with increasing temperature.Here we report a new type of extrinsic magnetoresistance. It is studied in pressed powders of CrO 2 , where it arises from contacts between particles.…”

mentioning

confidence: 99%

Magnetoresistance of Chromium Dioxide Powder Compacts

et al. 1998

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Cold-pressed powders of the half-metallic ferromagnet CrO 2 are dielectric granular metals. Hysteretic magnetoresistance with maxima at the coercive field arises from interparticle contacts. Dilution with insulating antiferromagnetic Cr 2 O 3 powder reduces the conductivity by 3 orders of magnitude, but enhances the magnetoresistance ratio which reaches 50% at 5K. The negative magnetoresistance is due to tunneling between contiguous ferromagnetic particles along a critical path with a spin-dependent Coulomb gap. [S0031-9007(98)05996-1] PACS numbers: 72.15. Gd, 73.40.Gk, 75.50.Cc, 81.20.Ev Negative magnetoresistance has been widely investigated in ferromagnetic metals and heterostructures. Effects intrinsic to a material are distinguished from extrinsic effects which depend on the direction of magnetization in adjacent ferromagnetic regions. Examples of the former include the anisotropic magnetoresistance of permalloy [1] or the colossal magnetoresistance of nonstoichiometric EuO [2] and mixed-valence manganites [3]. Examples of the latter are the giant magnetoresistance of multilayers [4] and granular metals [5,6] or the behavior of spin-dependent tunnel junctions [7], where resistivity is greatest at the coercive or switching field and decreases as the sample reaches technical saturation. Recent experiments on epitaxial manganite films with a single grain boundary have allowed the high-field, colossal magnetoresistance to be separated from the low-field effect due to heterogeneous magnetization distribution in adjacent grains [8,9]. A characteristic but unexplained feature of the low-field magnetoresistance in manganite ceramics [10], polycrystalline films [11,12], and tunnel junctions [13,14] is its rapid decay with increasing temperature.Here we report a new type of extrinsic magnetoresistance. It is studied in pressed powders of CrO 2 , where it arises from contacts between particles. Chromium dioxide is an ideal material for spin-polarized electron tunneling, as it is a half-metallic ferromagnet where complete spin polarization of the conduction electrons is maintained up to the surface [15]. There are two 3d electrons in spinsplit t 2g subbands, one localized and the other in a halffilled band [16]. The two electrons are strongly coupled by the on-site exchange interaction J H ഠ 1 eV. The intrinsic metallic nature of the oxide is illustrated by the resistivity of an oriented film grown on TiO 2 , shown in Fig. 1(a). It follows Matthiessen's rule with a residual resistivity of 0.1 mV m ͑10 mV cm͒ and a room-temperature value about 30 times greater. The slope dr͞dT remains positive above the Curie temperature ͑T C 396 K͒ [17]. The films exhibit only a small linear intrinsic magnetoresistance effect, ͑1͞m 0 r͒dr͞dH ϳ1%͞T at room temperature.Our samples were made from a commercial CrO 2 powder used for magnetic recording. The powder is composed of acicular single-domain particles with an average length of 300 nm and an aspect ratio of about 8:1. Coercivity is 59 mT (590 G) at room temperature, rising up to ...

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Low-field magnetoresistive properties of polycrystalline and epitaxial perovskite manganite films

Cited by 372 publications

References 14 publications

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHox
Raychaudhuri
¹
,
Sheshadri
²
,
Taneja
³

et al. 1999
Phys. Rev. B

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHox
Raychaudhuri
¹
,
Sheshadri
²
,
Taneja
³

et al. 1999
Phys. Rev. B

Magnetotransport properties of a single grain boundary in a bulk La–Ca–Mn–O material

Magnetoresistance of Chromium Dioxide Powder Compacts

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Low-field magnetoresistive properties of polycrystalline and epitaxial perovskite manganite films

Cited by 372 publications

References 14 publications

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHoxRaychaudhuri1, Sheshadri2, Taneja3 et al. 1999Phys. Rev. B

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHoxRaychaudhuri1, Sheshadri2, Taneja3 et al. 1999Phys. Rev. B

Magnetotransport properties of a single grain boundary in a bulk La–Ca–Mn–O material

Magnetoresistance of Chromium Dioxide Powder Compacts

Contact Info

Product

Resources

About

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHox
Raychaudhuri
¹
,
Sheshadri
²
,
Taneja
³

et al. 1999
Phys. Rev. B

Spin-polarized tunneling in the half-metallic ferromagnetsLa0.7−xHox
Raychaudhuri
¹
,
Sheshadri
²
,
Taneja
³

et al. 1999
Phys. Rev. B