Insulator-Metal Transition and Long-Range Magnetic Order in EuO

Penney, T.; Shafer, M. W.; Torrance, J. B.

doi:10.1103/physrevb.5.3669

Cited by 128 publications

(58 citation statements)

References 10 publications

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“…1(b). 1,10,27 The semiconducting behavior in the paramagnetic phase can be attributed to the Fermi level being located below the conduction band minimum, whereas in the ferromagnetic phase a large spin splitting (nearly 1 eV) shifts the Fermi level above the bottom of the spindown conduction band because of strong exchange interactions between Hg-6s and Cr-3d electrons [See insets in Fig. 1(b)].…”

Section: Resultsmentioning

confidence: 99%

“…18 The sd exchange interaction (or s-f interaction in rare earth compounds) provides strong polarizing force for a small number of lattice spins overlapping with the donor wavefunctions. 9,10,19,40,41 At high temperatures, spin correlation length ξ is too short to be relevant. The lattice spins in the polarons can thus be modeled as a uniformly polarized core of sub-nm size, separated by a sharp boundary from the paramagnetic background with randomized spins.…”

Section: Discussionmentioning

confidence: 99%

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Spin correlations and colossal magnetoresistance inHgCr2Se4

Lin

Shi

et al. 2016

Phys. Rev. B

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This study aims to unravel the mechanism of colossal magnetoresistance (CMR) observed in n-type HgCr2Se4, in which low-density conduction electrons are exchange-coupled to a threedimensional Heisenberg ferromagnet with a Curie temperature TC ≈ 105 K. Near room temperature the electron transport exhibits an ordinary semiconducting behavior. As temperature drops below T * ≃ 2.1 TC, the magnetic susceptibility deviates from the Curie-Weiss law, and concomitantly the transport enters an intermediate regime exhibiting a pronounced CMR effect before a transition to metallic conduction occurs at T < TC . Our results suggest an important role of spin correlations not only near the critical point, but also for a wide range of temperatures (TC < T < T * ) in the paramagnetic phase. In this intermediate temperature regime the transport undergoes a percolation type of transition from isolated magnetic polarons to a continuous network when temperature is lowered or magnetic field becomes stronger.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Spin correlations and colossal magnetoresistance inHgCr2Se4

Lin

Shi

et al. 2016

Phys. Rev. B

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“…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.…”

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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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“…The effect refers to a strong shift of the lower band edge to lower energies upon temperature cooling below T C . A further striking effect being due to the mentioned induced temperature dependence is a metal-insulator transition observed in Eu-rich EuO 4 . The Eu-richness manifests itself in (2+)-charged oxygen vacancies.…”

Section: Introductionmentioning

confidence: 99%

Kondo lattice model: Application to the temperature-dependent electronic structure of EuO(100) films

2001

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We present calculations for the temperature-dependent electronic structure and magnetic properties of thin ferromagnetic EuO films. The treatment is based on a combination of a multiband-Kondo lattice model with first-principles TB-LMTO band structure calculations. The method avoids the problem of double-counting of relevant interactions and takes into account the correct symmetry of the atomic orbitals. We discuss the temperature-dependent electronic structures of EuO(100) films in terms of quasiparticle densities of states and quasiparticle band structures. The Curie temperature TC of the EuO films turns out to be strongly thicknessdependent, starting from a very low value (≃ 15K) for the monolayer and reaching the bulk value at about 25 layers.

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Insulator-Metal Transition and Long-Range Magnetic Order in EuO

Abstract: Daniel has used an expression similar to Eq. (8) to compute the impurity resistivities of Cuand Au-based alloys containing transition-metal impurities. 5

Cited by 128 publications

References 10 publications

Spin correlations and colossal magnetoresistance inHgCr2Se4

Spin correlations and colossal magnetoresistance inHgCr2Se4

Magnetoresistance of Chromium Dioxide Powder Compacts

Kondo lattice model: Application to the temperature-dependent electronic structure of EuO(100) films

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