Effect of softening on colossal manganites

Sun, Shih-Jye; Lu, Wan-Chen; Chou, Hsiung

doi:10.1016/s0921-4526(02)01414-x

Cited by 8 publications

(12 citation statements)

References 26 publications

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“…Ref. [19] treated the effects of strong U by mapping the problem to a Hamiltonian with U = 0 [14] and renormalized hopping t(n). The magnon excitations were then described within the RPA.…”

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confidence: 99%

Non-Heisenberg spin dynamics of double-exchange ferromagnets with Coulomb repulsion

Kapetanakis¹,

Perakis²

2007

Phys. Rev. B

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With a variational three-body calculation we study the role of the interplay between the onsite Coulomb, Hund's rule, and superexchange interactions on the spinwave excitation spectrum of itinerant ferromagnets. We show that correlations between a Fermi sea electron-hole pair and a magnon result in a very pronounced zone boundary softening and strong deviations from the Heisenberg spinwave dispersion. We show that this spin dynamics depends sensitively on the Coulomb and exchange interactions and discuss its possible relevance to recent experiments in the manganites. PACS numbers: 75.30.Ds, 75.10.Lp, 75.47.Lx The interaction between itinerant carrier spins and localized magnetic moments leads to ferromagnetic order in a wide variety of systems [1]. Examples include the manganese oxides (manganites) R 1−x A x MnO 3 ( R=La, Pr, Nd, Sm, · · · and A= Ca, Ba, Sr, Pb, · · · ) [2] and the III-Mn-V ferromagnetic semiconductors [3]. Such systems are of great current interest due to their novel potential applications. For example, the manganites display colossal magnetoresistance [2], while ferromagnetic semiconductors raise the possibility of multifunctional quantum devices that combine information processing and storage on a single chip with low power consumption [4]. In such materials, the magnetic and transport properties are intimately related and can be controlled by varying the itinerant carrier concentration and dimensionality.In the manganites, n=1-x itinerant electrons per Mn atom partially fill a d-band with e g symmetry. Their concentration, n, is controlled by the hole doping, x. The d-band kinetic energy K is determined by the hopping energy between the neighboring lattice sites, t ∼ 0.2 − 0.5eV. The itinerant electron spins interact strongly with localized spin-S magnetic moments (Hund's rule coupling H exch with strength J ∼ 2eV> t). S=3/2 comes from the three electrons in the tightly bound t 2g orbitals. This ferromagnetic interaction competes with the direct antiferromagnetic interactions (H AF ) between neighboring local spins, J AF ∼ 0.01t. The largest energy scale in the manganites is given by the on-site Coulomb repulsion between the itinerant electrons, U ∼ 3.5 − 8eV (H U ). This Coulomb interaction is generally difficult to treat and its effects have received less attention. Here we focus on the role of U on the spin dynamics in the concentration range 0.5 ≤ n ≤ 0.8 where metallic behavior is observed in both 3D and quasi-2D (layered) manganites.The ferromagnetic order in the manganites can be interpreted to first approximation by invoking the double exchange mechanism and the J → ∞ limit of the minimal Hamiltonian K + H exch [2,5]. An itinerant carrier is allowed to hop on a lattice site only if its spin is parallel to the local spin on that site. The kinetic en-ergy is thus reduced when all spins are parallel. This favors the ferromagnetic state |F , which describes local spins with S z = S on all lattice sites and a Fermi sea of spin-↑ electrons. The above spins are often treated as classical,...

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“…Ref. [19] treated the effects of strong U by mapping the problem to a Hamiltonian with U = 0 [14] and renormalized hopping t(n). The magnon excitations were then described within the RPA.…”

mentioning

confidence: 99%

Non-Heisenberg spin dynamics of double-exchange ferromagnets with Coulomb repulsion

Kapetanakis¹,

Perakis²

2007

Phys. Rev. B

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“…Among the accessible questions on QCs, the structures of Al-based decagonal QCs (DQCs) have been widely investigated because there is one periodic axis, which is advanta-geous for solving their crystal structures (Bendersky, 1985;Ma & Kuo, 1992;Sun & Hiraga, 2002;Hiraga & Yasuhara, 2013). The basic structural blocks of Al-based DQCs and their approximants with a periodicity of about 1.2 nm are primarily decorated rhombus, star, boat, hexagon and decagon tiles (Steurer, 2004;Cockayne & Widom, 1998;Gummelt, 2006;Engel & Trebin, 2006;He et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Quasicrystal-related mosaics with periodic lattices interlaid with aperiodic tiles

Shen

et al. 2020

Acta Cryst Sect A

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Quasicrystals, which have long‐range orientational order without translational symmetry, are incompatible with the theory of conventional crystals, which are characterized by periodic lattices and uniformly repeated unit cells. Reported here is a novel quasicrystal‐related solid state observed in two Al–Cr–Fe–Si alloys, which can be described as a mosaic of aperiodically distributed unit tiles in translationally periodic structural blocks. This new type of material possesses the opposing features of both conventional crystals and quasicrystals, which might trigger wide interest in theory, experiments and the potential applications of this type of material.

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“…For small deviations from equilibrium, the dynamical magnetic properties are determined by the spin susceptibility. 6,7,8,9,10 Within the Random Phase approximation (RPA), 7,11,12,13,14,15,16 which gives the spin susceptibility to O(1/S) (S is the local spin magnitude), magnetization relaxation arises from the interplay between the dephasing of the itinerant carrier spin and the magnetic exchange interaction. 8,9,10,17 Spin relaxation also arises from inelastic scattering processes, such as magnon scattering with charge excitations.…”

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confidence: 99%

Magnetization relaxation and collective spin excitations in correlated double-exchange ferromagnets

Kapetanakis

Perakis

2008

Phys. Rev. B

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We study spin relaxation and dynamics of collective spin excitations in correlated double-exchange ferromagnets. For this, we introduce an expansion of the Green's functions equations of motion that treats non-perturbativerly all correlations between a given number of spin and charge excitations and becomes exact within a sub-space of states. Our method treats relaxation beyond Fermi's Golden Rule while recovering previous variational results for the spin-wave dispersion. We find that the momentum dependence of the spin-wave dephasing rate changes qualitatively due to the on-site Coulomb interaction, in a way that resembles experiment, and depends on its interplay with the magnetic exchange interaction and itinerant spin lifetime. We show that the collective spin relaxation and its dependence on the carrier concentration depends sensitively on three-body correlations between a spin excitation and a Fermi sea electron and hole. The above spin dynamics can be controlled via the itinerant carrier population.

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Effect of softening on colossal manganites

Cited by 8 publications

References 26 publications

Non-Heisenberg spin dynamics of double-exchange ferromagnets with Coulomb repulsion

Non-Heisenberg spin dynamics of double-exchange ferromagnets with Coulomb repulsion

Quasicrystal-related mosaics with periodic lattices interlaid with aperiodic tiles

Magnetization relaxation and collective spin excitations in correlated double-exchange ferromagnets

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