Giant magnetoresistance in epitaxial Nd0.7Sr0.3MnO3−δ thin films

Xiong, Ge; Li, Q.; Ju, Honglyoul; Mao, Sining; Senapati, L.; Xi, X. X.; Greene, R. L.; Venkatesan, T.

doi:10.1063/1.113267

Cited by 312 publications

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“…͓S0163-1829͑97͒04513-X͔ Interest in mixed-valence manganites of the ͑La 0.7 Ca 0.3 ͒MnO 3 type has revived 1 with the observations of large negative magnetoresistive effects, 2,3 especially in suitably annealed thin films. 4 The magnetoresistance is greatest in the vicinity of the Curie point T C of ferromagnetic compositions which exhibit ''metallic'' ͑temperature-independent͒ conduction at low temperatures and thermally activated conduction above T C . These compositions have a structure which is a variant of the cubic perovskite cell where the Mn-O bond lengths are unequal and Mn-O-Mn bond angles differ from 180°.…”

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“…4 The magnetoresistance is greatest in the vicinity of the Curie point T C of ferromagnetic compositions which exhibit ''metallic'' ͑temperature-independent͒ conduction at low temperatures and thermally activated conduction above T C . These compositions have a structure which is a variant of the cubic perovskite cell where the Mn-O bond lengths are unequal and Mn-O-Mn bond angles differ from 180°.…”

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confidence: 99%

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Magnetic localization in mixed-valence manganites

1997

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The metal-insulator transition is mixed-valence manganites of the ͑La 0.7 Ca 0.3 ͒MnO 3 type is ascribed to a modification of the spin-dependent potential J H s-S associated with the onset of magnetic order at T C . Here J H is the on-site Hund's-rule exchange coupling of an e g electron with sϭ1/2 to the t 2g ion core with S ϭ3/2. Above T C , the e g electrons are localized by the random spin-dependent potential and conduction is by variable-range hopping. Over the whole temperature range, the resistivity varies as ln( / ϱ ) ϭ͓T 0 ͕1Ϫ(M /M S ) 2 ͖/T͔ 1/4 , where M /M S is the reduced magnetization. The temperature and field dependence of the resistivity deduced from the molecular-field theory of the magnetization reproduces the experimental data over a wide range of temperature and field. ͓S0163-1829͑97͒04513-X͔ Interest in mixed-valence manganites of the ͑La 0.7 Ca 0.3 ͒MnO 3 type has revived 1 with the observations of large negative magnetoresistive effects, 2,3 especially in suitably annealed thin films. 4 The magnetoresistance is greatest in the vicinity of the Curie point T C of ferromagnetic compositions which exhibit ''metallic'' ͑temperature-independent͒ conduction at low temperatures and thermally activated conduction above T C . These compositions have a structure which is a variant of the cubic perovskite cell where the Mn-O bond lengths are unequal and Mn-O-Mn bond angles differ from 180°. 5 Their electronic properties are related to electron hopping among the Mn ions in octahedral sites; metallic conductivity and ferromagnetism are closely related and are generally interpreted in terms of the doubleexchange mechanism. 6 A spin-polarized * conduction band of mainly 3d(e g ↑) character 7 is supposed to be responsible for the ''metallic'' character of the current transport below T C . 8 The Mn 3ϩ ion has one e g electron, whereas the Mn 3ϩ ion has none. When the concentration of the divalent A-site cation ͑Ca, for example͒ is 0.3, the occupancy of the * band is 0.7, which corresponds to the strongest ferromagnetism and the greatest magnetoresistance. Electron transfer with spin memory is an essential ingredient for an understanding of the transport properties of mixed-valence manganites, but something more is needed to account for the metal-insulator transition near the Curie point. 9 The change of conduction regime below T C appears to be brought about by the onset of ferromagnetism. As temperature decreases, the magnetization increases and the resistivity drops. Resistivity has been reported to vary like ͓1Ϫ(M /M S ) 2 ͔, as in conventional giant magnetoresistance ͑GMR͒ systems, 10 but others find an exponential dependence 11 ln( )ϳϪM/M S . Here we propose the concept of magnetic localization to relate the resistivity at any temperature or applied field to the local magnetization, evaluated in the molecular field approximation. The model involves variable range hopping and goes beyond the purely phenomenological parallel conduction model of Nunez-Reiguero and Kadin. 12 We previously observed an impr...

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Magnetic localization in mixed-valence manganites

1997

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“…4 In case of Co-doped TiO 2 , the exact determination of T C was difficult because the amount of oxygen vacancies is spontaneously varied at high temperature, resulting in unintentional change in carrier density. 12 For several ferromagnetic compounds such as (La, Sr)MnO 3 and other perovskite manganites, [13][14][15] a kink in temperature dependence of resistivity is used to assign T C , as a result of carrier scattering induced near T C . Recently, the Kouvel-Fischer (KF) plot 16 was also used to cross-evaluate T C of (Ga,Mn)As in comparison with that obtained from kink structure.…”

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Curie temperature of Co-doped TiO2 as functions of carrier density and Co content evaluated from electrical transport and magnetization at low temperature regime

2016

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Curie temperature (TC) of anatase Co-doped TiO2 epitaxial thin films was systematically investigated as functions of carrier density (n) and Co content (x) by electrical transport and magnetization measurements at low temperature regime. The estimated TC from both measurements showed similar TC. For x = 0.03, 0.05, and 0.07, non-monotonic TC vs. n relations were observed, whereas TC was monotonically increasing function of n for x = 0.10. Possible mechanism of high TC ferromagnetism for this compound was discussed.

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“…Thus, at the link mn used in Eqs. (2)(3)(4), and working at large J H , the problem reduces to two electrons forming a spin S ′ = 1 in one site, interacting with one electron (i.e. a S ′ = 1/2 hole) at the other site.…”

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“…[1] A decrease in resistivity of four orders of magnitude has been observed in thin films of Nd 0.7 Sr 0.3 MnO 3 at fields of ∼ 8T . [2] The phase diagram of La 1−x Ca x MnO 3 is very rich with ferromagnetic (metal and insulator) phases, as well as regions where charge-ordering is observed. [3] The magnetic and electronic properties of these manganese oxides are believed to arise, at least in part, from the strong coupling between correlated itinerant electrons and localized spins, both of 3d character.…”

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Electronic Hamiltonian for transition-metal oxide compounds

1996

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An effective electronic Hamiltonian for transition metal oxide compounds is presented. For Mnoxides, the Hamiltonian contains spin-2 "spins" and spin-3/2 "holes" as degrees of freedom. The model is constructed from the Kondo-lattice Hamiltonian for mobile eg electrons and localized t2g spins, in the limit of a large Hund's coupling. The effective electron bond hopping amplitude fluctuates in sign as the total spin of the bond changes. In the large spin limit, the hopping amplitude for electrons aligned with the core ions is complex and a Berry phase is accumulated when these electrons move in loops. The new model is compared with the standard double exchange Hamiltonian. Both have ferromagnetic ground states at finite hole density and low temperatures, but their critical temperatures could be substantially different due to the frustration effects induced by the Berry phase. 75.30.Et, 75.50.Cc The discovery of giant magnetoresistance effects in ferromagnetic metallic oxides R 1−x X x MnO 3 (where R = La, Pr, Nd; X = Sr, Ca, Ba, Pb) has triggered renewed attention into these compounds.[1] A decrease in resistivity of four orders of magnitude has been observed in thin films of Nd 0.7 Sr 0.3 MnO 3 at fields of ∼ 8T .[2] The phase diagram of La 1−x Ca x MnO 3 is very rich with ferromagnetic (metal and insulator) phases, as well as regions where charge-ordering is observed.[3] The magnetic and electronic properties of these manganese oxides are believed to arise, at least in part, from the strong coupling between correlated itinerant electrons and localized spins, both of 3d character. The Mn 3+ ions have three electrons in the t 2g state forming a local S=3/2 spin, and one electron in the e g state which hops between nearestneighbor Mn-ions, with double occupancy suppressed by Coulombic repulsion. The widely used Hamiltonian to describe manganese oxides is [4]where the first term is the e g electron transfer between nearest-neighbor Mn-ions at sites m, n, while the second term is the ferromagnetic Hund coupling between the S=3/2 localized spin S n and the mobile electron with spin σ n (J H > 0). A Coulombic repulsion to suppress double occupancy in the itinerant band is implicit. The on-site Hund coupling energy is larger than the conduction bandwidth favoring the alignment of the itinerant and localized spins. For Mn 3+ , the resulting spin is 2, while for Mn 4+ (vacant e g state) the spin is 3/2. Since the study of Hamiltonian Eq.(1) is a formidable task, simplifications have been introduced to analyze its properties. A familiar approach is the use of the doubleexchange Hamiltonian, [4][5][6][7][8][9] where the e g electrons move in the background of classical spins S cl n that approximate the S=3/2 almost localized t 2g electrons. The conduction electron effective hopping between sites m and n used in previous work is t ef f mn = t 1 + (S cl m · S cl n /S 2 ), where S is the magnitude of the classical spin. [4,6] Using this model, the ferromagnetic critical temperature, T c , was recently estimated.[9] Since t...

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Giant magnetoresistance in epitaxial Nd0.7Sr0.3MnO3−δ thin films

Cited by 312 publications

References 0 publications

Magnetic localization in mixed-valence manganites

Magnetic localization in mixed-valence manganites

Curie temperature of Co-doped TiO2 as functions of carrier density and Co content evaluated from electrical transport and magnetization at low temperature regime

Electronic Hamiltonian for transition-metal oxide compounds

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