The Relation between Electrical Conductivity Mechanisms and Magnetic After-Effects in Single Crystal Magnetite

Lenge, N.; Kronmüller, H.; Walz, F.

doi:10.1143/jpsj.53.1406

Cited by 29 publications

(23 citation statements)

References 21 publications

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“…This dependence can be quantitatively expressed by Mott's variable range hopping ͑VRH͒ ͑T 0 / T͒ 1/4 law, which is widely used for the approximation of magnetite resistivity below T V . 20,21 The experimental data presented in the inset of Fig. 1͑a͒ show that the resistivity could be reasonably linearized in ln͑͒ − ͑1/T͒ 1/4 axis.…”

Section: A Dense Polycrystalsmentioning

confidence: 73%

“…The absolute room temperature resistivity value is 5.5± 0.5ϫ 10 −3 ⍀ cm, that is very close to the 4.5± 0.5ϫ 10 −3 ⍀ cm reported for the stoichiometric monocrystal. 19,20 Thus, the resistivity data indicate that the GB partial resistance is negligibly small for these samples. This is consistent with the lack of MR effect within 0.05% detection limit.…”

Section: A Dense Polycrystalsmentioning

confidence: 93%

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Effect of grain boundaries on the magnetoresistance of magnetite

et al. 2005

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The effects of grain boundary morphology and stoichiometry had been systematically examined to clarify the role of natural grain boundaries in magnetoresistance of magnetite Fe 3͑1−␦͒ O 4 . We found that the excess resistance, caused by presence of the grain boundaries, is negligibly low in stoichiometric polycrystals. Accordingly, there was no grain boundary magnetoresistance detected in dense polycrystals. Moreover, the incorporation of grain boundaries was found to decrease the resistance of polycrystalline samples below the Verwey transition temperature. That was connected to the enhanced conductivity of grain boundaries appearing due to the local suppression of charge ordering. On the other hand, the essential negative magnetoresistance was detected in granular samples, exploring the point contact geometry for intergrain contacts. That magnetoresistance is characterized by large high-field component and appearance over a wide range of oxidation. It has been explained within the model of magnetically inhomogeneous grain boundary with the characteristic magnetic thickness of the order of exchange length. The magnetoresistance effect was connected to the spin-dependent scattering at the transition layers of magnetization formed around hard magnetic defects. The contraction of these transition layers by external magnetic field is supposed to provide the origin of the observed magnetoresistance. The analysis of appropriate microscopic scattering mechanisms reveals the important role of point defects in the spin-dependent scattering. The second magnetoresistance component was separated at highly oxidized grain boundaries and associated with tunneling transport across the isolating grain boundaries. Although the oxidation was shown to improve the isolating properties of natural grain boundaries, the performance of oxidized grain boundary as a tunneling barrier is still poor.

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Section: A Dense Polycrystalsmentioning

confidence: 73%

Section: A Dense Polycrystalsmentioning

confidence: 93%

Effect of grain boundaries on the magnetoresistance of magnetite

et al. 2005

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“…Other similar measurements [11][12][13] suggest Arrhenius-like temperature-activated ρ(T ) dependence or Mott's VRH dependence valid only over limited temperature range.…”

Section: Resultsmentioning

confidence: 65%

Link between Magnetic and Dielectric Properties in Magnetite

2010

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We have measured temperature dependence of magnetic and dielectric properties in high quality stoichiometric single-crystals of magnetite (Fe3O4). At low temperatures, below the Verwey transition, both ac susceptibility and ac permittivity reveal similar relaxation processes. We discuss these effects in connection with domain structure and variable range hopping mechanism of electrical conductivity.PACS numbers: 71.30.+h, 75.60.−d, 75.85.+t 1. Introduction Magnetite -a mixed valence iron oxide, Fe 3 O 4 , with cubic inverse spinel structure at room temperature -is a prototype ferrimagnetic system that still attracts considerable attention mainly due to the presence of the so-called Verwey transition -a structural phase transition accompanied by substantial changes of magnetic and electrical properties [1]. Although Mott's metalinsulator transition theory [2] was well suited to explain the sharp increase of resistivity of magnetite upon cooling through the Verwey temperature (T V ≈ 120 K), the exact nature of the transition is still unresolved and the charge ordering on the Fe ions has not been sufficiently clarified [3][4][5][6]. To complicate the matter even further, upon cooling through T V the structure changes to monoclinic [5] and the monocrystal splits into structural domains which are strongly linked to the instantaneous magnetic domain structure of the sample (i.e. random in weak magnetic fields). The interplay of spin, lattice and electronic degrees of freedom makes this strongly correlated system a potential candidate for novel applications [7].In this work we focus not on the Verwey transition itself but rather on the magnetic and dielectric behavior of magnetite below T V .2. Experimental Stoichiometric single crystals of magnetite were grown by floating zone technique [8] and cut to disk shape 5 mm in diameter and 1 mm thick, the disk axis corresponds to 100 crystallographic direction. Two silver electrodes (4 mm in diameter) were deposited on the flat surfaces of the disk by means of magnetron sputtering. A custom sample holder with copper and brass contacts was used to measure both electrical and magnetic properties simultaneously. To measure the magnetic properties (complex ac susceptibility, dc magnetization) a home--built continuously reading SQUID magnetometer with immobile sample was used [9]. The magnetometer oper-

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“…Electrical properties of Fe 3 O 4 have received much attention since the original work of Verwey [1][2][3][4][5][6][7][8][9][10][11][12]. The discontinuous conductivity transition in magnetite is possibly one of the most striking manifestations of electron correlation effects.…”

Section: Introductionmentioning

confidence: 99%