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Ling, Chris D.; Millburn, J. E.; Mitchell, J. F.; Argyriou, D. N.; Linton, J.; Bordallo, Heloisa N.

doi:10.1103/physrevb.62.15096

Cited by 137 publications

(145 citation statements)

References 40 publications

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“…Also in bilayer La 2−2x Sr 1+2x Mn 2 O 7 manganites a competition between magnetic interactions of different origin was observed, resulting in rather complex phase diagram, 11,12 which is a challenge for the theoretical models. At higher doping x ∼ 0.45 the magnetic order changes from FM to A-AF phase.…”

Section: Introductionmentioning

confidence: 99%

Doping dependence of spin and orbital correlations in layered manganites

et al. 2006

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We investigate the interplay between spin and orbital correlations in monolayer and bilayer manganites using an effective spin-orbital t-J model which treats explicitly the eg orbital degrees of freedom coupled to classical t2g spins. Using finite clusters with periodic boundary conditions, the orbital many-body problem is solved by exact diagonalization, either by optimizing spin configuration at zero temperature, or by using classical Monte-Carlo for the spin subsystem at finite temperature. In undoped two-dimensional clusters, a complementary behavior of orbital and spin correlations is found -the ferromagnetic spin order coexists with alternating orbital order, while the antiferromagnetic spin order, triggered by t2g spin superexchange, coexists with ferro-orbital order. With finite crystal field term, we introduce a realistic model for La1−xSr1+xMnO4, describing a gradual change from predominantly out-of-plane 3z 2 − r 2 to in-plane x 2 − y 2 orbital occupation under increasing doping. The present electronic model is sufficient to explain the stability of the CE phase in monolayer manganites at doping x = 0.5, and also yields the C-type antiferromagnetic phase found in Nd1−xSr1+xMnO4 at high doping. Also in bilayer manganites magnetic phases and the accompanying orbital order change with increasing doping. Here the model predicts C-AF and G-AF phases at high doping x > 0.75, as found experimentally in La2−2xSr1+2xMn2O7.

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Section: Introductionmentioning

confidence: 99%

Doping dependence of spin and orbital correlations in layered manganites

et al. 2006

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“…Recently the nanoscale granularity in manganese oxides was directly observed experimentally in La 2−2x Sr 1+2x Mn 2 O 7 , [29]. The cluster structure in these perovskite materials is introduced by dopants, creating the individual weakly coupled nanodomains.…”

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confidence: 99%

Electron Transport in Nanogranular Ferromagnets

2007

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We study electronic transport properties of ferromagnetic nanoparticle arrays and nanodomain materials near the Curie temperature in the limit of weak coupling between the grains. We calculate the conductivity in the Ohmic and non-Ohmic regimes and estimate the magnetoresistance jump in the resistivity at the transition temperature. The results are applicable for many emerging materials, including artificially self-assembled nanoparticle arrays and a certain class of manganites, where localization effects within the clusters can be neglected.PACS numbers: 73.43.Qt Arrays of ferromagnetic nanoparticles are becoming one of the mainstreams of current mesoscopic physics [1,2,3,4]. Not only ferromagnetic granules promise to serve as logical units and memory storage elements meeting elevated needs of emerging technologies, but also offer an exemplary model system for investigation of disordered magnets. At the same time the model of weakly coupled nanoscale ferromagnetic grains proved to be useful for understanding the transport properties of doped manganite systems [5,6] that have intrinsic inhomogeneities. Recent studies showed that above the Curie temperature these materials possess a nanoscale ferromagnetic cluster structure which to a large extend controls transport in these systems [7,8,9,10]. This defines an urgent quest for understanding and quantitative description of electronic transport in ferromagnetic nanodomain materials based on the model of nanogranular ferromagnets.In this paper we investigate electronic transport properties of arrays of ferromagnetic grains [11] near the ferromagnetic-paramagnetic transition, see Fig. 1. At low temperatures, T < T s c , the sample is in a so called superferromagnetic (SFM) state, see Fig. 1, set up by dipole-dipole interactions. Near the macroscopic Curie temperature, T s c , thermal fluctuations destroy the macroscopic ferromagnetic order. At intermediate temperatures T s c < T < T g c , where T g c is the Curie temperature of a single grain, the system is in a superparamagnetic (SPM) state where each grain has its own magnetic moment while the global ferromagnetic order is absent. At even higher temperatures, T > T g c , the ferromagnetic state within each grain is destroyed and the complete sample is in a paramagnetic state. We consider the model of weakly interacting grains in which the sample Curie temperature is much smaller than the Curie temperature of a single grain, T s c ≪ T g c . We first focus on the SPM state, and discuss a d−dimensional array (d = 3, 2) of ferromagnetic grains taking into account Coulomb interactions between electrons. Granularity introduces additional energy parameters apart from the two Curie temperatures, T g c and T s c : each nanoscale cluster is characterized by (i) the charging c , where T s c is the macroscopic Curie temperature of the system, the ferromagnetic grains (superspins) form a superferromagnet (SFM); for T s c < T < T g c , where T g c is the Curie temperature for a single grain, the system is in a superparamagne...

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“…However, the change in dimensionality and resulting pronounced cation dependence of the electronic properties can produce physical properties which contrast strongly with the perovskite systems [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…One of the most interesting regions extends from x=0.3 to x=0. 4 where ferromagnetic metals (FMM) are found. However, also within a so relatively narrow doping range several different kinds of arrangements of manganese ions spin occur.…”

Section: Introductionmentioning

confidence: 99%

Absence of Long-Range Magnetic Order in the La_1.4Sr_0.8Ca_0.8Mn₂O₇ Bilayered Manganite

Malavasi¹,

Mozzati²,

Pomjakushin³

et al. 2006

J. Phys. Chem. B

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In this work we studied, by means of high-resolution neutron diffraction as a function of temperature, the La 1.4 Sr 0.8 Ca 0.8 Mn 2 O 7 bilayered manganite for two different annealing treatments. Out data allowed us to shown, for the first time, the absence of long-range magnetic order in this optimally doped bilayered manganite where the A-site of the structure is doped with equal proportions of different isovalent cations (Ca and Sr). The system, however, presents defined IM transitions which suggest that the transport properties are not linked to the evolution of long-range order and that two dimensional spin ordering in the layers of the perovskite blocks may be sufficient to "assist" the hole hopping.Possible reason for the suppression of magnetic order induced by the Ca doping is a size effect coupled to the cation size mismatch between the Sr and Ca ions. IntroductionThere is an increasing interest in materials that show magnetoresistance, because of their use in magnetic information storage or as magnetic field sensors [1]. Most of the available theoretical and experimental work has, until now, been focused on the 3D perovskite structures, that is the n=∞ endmember of the A n+1 B n O 3n+1 Ruddlesden-Popper family, in which n 2D layers of BO 6 corner-sharing octahedra are joined along the stacking direction and separated by rock-salt AO layers.The optimally-doped n=2 members of this family (La 2-2x B 1+2x Mn 2 O 7 where B = Ca or Sr) behave analogously to the n=∞ manganites in the sense that they undergo an insulating-to metallic-like state (I-M) transition coupled to a ferromagnetic transition at temperatures around 120-140 K; besides, they present a large magnetoresistance in this temperature range [2]. However, the change in dimensionality and resulting pronounced cation dependence of the electronic properties can produce physical properties which contrast strongly with the perovskite systems [3][4][5][6].In the n=2 member La 2-2x Sr 1+2x Mn 2 O 7 an extremely rich variety of magnetic phases have been found as a function of the Sr-doping. One of the most interesting regions extends from x=0.3 to x=0.4 where ferromagnetic metals (FMM) are found. However, also within a so relatively narrow doping range several different kinds of arrangements of manganese ions spin occur. A common property is the presence of a 2D ferromagnetic ordering in each perovskite layer and between the MnO 2 layers even though with different spin directions as a function of x. At x=0.3, the magnetic moments of each MnO 2 layer couple ferromagnetically within a bilayer and antiferromagnetically, along the c-axis, between successive bilayers. At x≈0.32 the inter-bilayer coupling becomes FM but still directed along the c-axis.At x≥0.33 the magnetic moments direct along the ab-plane. The magnetic coupling between the constituents single MnO 2 layers changes from FM into canted-antiferromagnetic (AFM) beyond x~0.4 [7]. Also the magnetic coupling above the transition temperature (T C ) is rather interesting. As suggested by several gro...

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Interplay of spin and orbital ordering in the layered colossal magnetoresistance manganiteLa2−2xSr1+2

Cited by 137 publications

References 40 publications

Doping dependence of spin and orbital correlations in layered manganites

Doping dependence of spin and orbital correlations in layered manganites

Electron Transport in Nanogranular Ferromagnets

Absence of Long-Range Magnetic Order in the La_1.4Sr_0.8Ca_0.8Mn₂O₇ Bilayered Manganite

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Interplay of spin and orbital ordering in the layered colossal magnetoresistance manganiteLa2−2xSr1+2

Cited by 137 publications

References 40 publications

Doping dependence of spin and orbital correlations in layered manganites

Doping dependence of spin and orbital correlations in layered manganites

Electron Transport in Nanogranular Ferromagnets

Absence of Long-Range Magnetic Order in the La1.4Sr0.8Ca0.8Mn2O7 Bilayered Manganite

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Absence of Long-Range Magnetic Order in the La_1.4Sr_0.8Ca_0.8Mn₂O₇ Bilayered Manganite