Spin Interactions in bcc and fcc Fe beyond the Heisenberg Model

Singer, Reinhard; Dietermann, F.; Fähnle, M.

doi:10.1103/physrevlett.107.017204

Cited by 46 publications

(31 citation statements)

References 21 publications

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“…It is therefore unsurprising that in metallic magnetic materials such interactions cannot be only described in simple pairwise terms, but must also include interactions over groups of sites. Many authors in the past have found theoretical evidence of the existence and importance of terms beyond a simple Heisenberg picture [44][45][46][47][48] . An indication of their presence follows directly from the calculation of effective pairwise interactions which adopt different values when evaluated from different magnetic states.…”

Section: A Hierarchy Of Local Moment Correlationsmentioning

confidence: 99%

Ab initiotheory of the Gibbs free energy and a hierarchy of local moment correlation functions in itinerant electron systems: The magnetism of theMn3Amaterials class

Mendive-Tapia

Staunton

2019

Phys. Rev. B

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We present an ab-initio disordered local moment theory for the Gibbs free energy of a magnetic material. Two central objects are calculated: the lattice Fourier transform of the direct local moment -local moment correlation functions in the paramagnetic state and local internal magnetic fields as functions of magnetic order. We identify the potentially most stable magnetic phases from the first, which can include non-collinear and long-period states in complex multi-atom unit cells, and extract higher order correlations among the local moments from the second. We propose that these latter entities produce a picture of effective multi-site magnetic interactions depending on the state and extent of magnetic order and discuss its relation to other approaches. We show how magnetic phase diagrams for temperature, magnetic field, and lattice structure and also magnetocaloric and mechanocaloric effects can be obtained from this approach. The theory accurately predicts the order of transitions and quantifies contributions to first-order and order-order magnetic phase transitions from both purely electronic sources and magnetoelastic effects. Our case study is the apparently frustrated magnetism of the Mn3A class of materials in all its cubic, hexagonal, and tetragonal structures. The theory produces magnetic phases and transition temperatures in good agreement with experiment. We explain the first-order triangular antiferromagnetic to collinear antiferromagnetic transition in cubic Mn3Pt as a magnetovolume driven effect, and its absence for A=Ir and Rh. We also construct the magnetic phase diagram of Mn3Pt and explore its potential as a barocaloric material. Finally, we prepare the groundwork for future fully relativistic studies of the temperature dependence of the magnetism of Mn3A, including Mn3Sn, Mn3Ga, and Mn3Ge. arXiv:1812.08653v2 [cond-mat.mtrl-sci]

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Section: A Hierarchy Of Local Moment Correlationsmentioning

confidence: 99%

Ab initiotheory of the Gibbs free energy and a hierarchy of local moment correlation functions in itinerant electron systems: The magnetism of theMn3Amaterials class

Mendive-Tapia

Staunton

2019

Phys. Rev. B

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“…With the advent of high performance computational resources, advanced first-principles techniques can now be applied to study the magnetic and electronic structure of Fe at elevated temperature. These include the dynamical mean field theory (DMFT) [5,[8][9][10][11][12][13][14], Hubbard models [15], the dynamical coherent potential approximation [16], extended Heisenberg models based on parameters calculated with density functional theory [17][18][19][20][21], spin cluster expansions [22][23][24], or spin-fluctuation theory [6]. For an overview of the recent advances in this field see, e.g., Refs.…”

Section: Introductionmentioning

confidence: 99%

Strong impact of lattice vibrations on electronic and magnetic properties of paramagnetic Fe revealed by disordered local moments molecular dynamics

et al. 2016

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We study the impact of lattice vibrations on magnetic and electronic properties of paramagnetic bcc and fcc iron at finite temperature, employing the disordered local moments molecular dynamics (DLM-MD) method. Vibrations strongly affect the distribution of local magnetic moments at finite temperature, which in turn correlates with the local atomic volumes. Without the explicit consideration of atomic vibrations, the mean local magnetic moment and mean field derived magnetic entropy of paramagnetic bcc Fe are larger compared to paramagnetic fcc Fe, which would indicate that the magnetic contribution stabilizes the bcc phase at high temperatures. In the present study we show that this assumption is not valid when the coupling between vibrations and magnetism is taken into account. At the γ -δ transition temperature (1662 K), the lattice distortions cause very similar magnetic moments of both bcc and fcc structures and hence magnetic entropy contributions. This finding can be traced back to the electronic densities of states, which also become increasingly similar between bcc and fcc Fe with increasing temperature. Given the sensitive interplay of the different physical excitation mechanisms, our results illustrate the need for an explicit consideration of vibrational disorder and its impact on electronic and magnetic properties to understand paramagnetic Fe. Furthermore, they suggest that at the γ -δ transition temperature electronic and magnetic contributions to the Gibbs free energy are extremely similar in bcc and fcc Fe.

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“…The approach described here is aimed at finding the most relevant part of the space of spin configurations, and to evaluate as accurately as possible the interatomic exchange interaction here. This is different from the approach of spin-cluster expansions that aim at introducing sufficiently many terms (of the order of several 30-50) in an expansion of the exchange energy [23], so that a good description of any possible configuration could be obtained, albeit without self-consistency of the atomic spin system. Whether cluster expansions, or the approach proposed here, is better suited to in general describe the dynamics of magnetic materials becomes a numerical exercise where the two different methods should be compared in how they reproduce a large body of experimental finitetemperature data.…”

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confidence: 95%

Interatomic Exchange Interactions for Finite-Temperature Magnetism and Nonequilibrium Spin Dynamics

et al. 2013

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We derive ab inito exchange parameters for general noncollinear magnetic configurations, in terms of a multiple scattering formalism. We show that the general exchange formula has an anisotropiclike term even in the absence of spin-orbit coupling, and that this term is large, for instance, for collinear configuration in bcc Fe, whereas for fcc Ni it is quite small. We demonstrate that keeping this term leads to what one should consider a biquadratic effective spin Hamiltonian even in the case of collinear arrangement. In noncollinear systems this term results in new tensor elements that are important for exchange interactions at finite temperatures, but they have less importance at low temperature. To illustrate our results in practice, we calculate for bcc Fe magnon spectra obtained from configuration-dependent exchange parameters, where the configurations are determined by finite-temperature effects. Our theory results in the same quantitative results as the finite-temperature neutron scattering experiments.

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Spin Interactions in bcc and fcc Fe beyond the Heisenberg Model

Cited by 46 publications

References 21 publications

Ab initiotheory of the Gibbs free energy and a hierarchy of local moment correlation functions in itinerant electron systems: The magnetism of theMn3Amaterials class

Ab initiotheory of the Gibbs free energy and a hierarchy of local moment correlation functions in itinerant electron systems: The magnetism of theMn3Amaterials class

Strong impact of lattice vibrations on electronic and magnetic properties of paramagnetic Fe revealed by disordered local moments molecular dynamics

Interatomic Exchange Interactions for Finite-Temperature Magnetism and Nonequilibrium Spin Dynamics

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