Mechanisms and origins of half-metallic ferromagnetism in CrO2 / Solovyev I. V.,Kashin I. V.,Mazurenko V. V. // PHYSICAL REVIEW B. - 2015. - V. 92, l. 14.

ISSN/EISSN:

2469-9950 / 2469-9969

Type:

Article

Abstract:

Using a realistic low-energy model, derived from the first-principles electronic structure calculations, we investigate the behavior of interatomic exchange interactions in CrO2, which is regarded to be one of the canonical half-metallic (HM) ferromagnetics. For these purposes we employ the dynamical mean-field theory (DMFT), based on the exact diagonalization of the effective Anderson impurity Hamiltonian, which was further supplemented with the theory of infinitesimal spin rotations for the exchange interactions. In order to elucidate the relative roles played by static and dynamic electron correlations, we compare the obtained results with several static techniques, including the unrestricted Hartree-Fock (HF) approximation, static DMFT (corresponding to the infinite frequency limit for the self-energy), and optimized effective potential method for treating the correlation interactions in the random-phase approximation. Our results demonstrate that the origin of the HM ferromagnetism in CrO2 is highly nontrivial. As far as the interactions in the neighboring coordination spheres are concerned, HF and DMFT methods produce very similar results, due to the partial cancellation of ferromagnetic (FM) double-exchange and antiferromagnetic (AFM) superexchange contributions, which represent two leading terms in the (Delta(Sigma) over cap)(-1) expansion for the exchange interactions (Delta(Sigma) over cap being the intra-atomic spin splitting). Both contributions are weaker in the HF approximation due to, respectively, additional orbital polarization of the t(2g) states and neglect of dynamic correlations. The role of higher-order terms in the (Delta(Sigma) over cap)(-1) expansion is twofold. On the one hand, they give rise to additional FM contributions to the neighboring exchange interactions, which tend to stabilize the FM state. On the other hand, they produce AFM long-range interactions, which make the FM state unstable in the single-site DMFT calculations for the minimal model, consisting of the t(2g) bands. Thus, the robust ferromagnetism in the minimal model, which can be easily obtained using static approximations, is fortuitous and this picture is largely revised at the level of more rigorous DMFT approach. We argue that the main ingredients, which are missing in the minimal model, are the direct exchange interactions and the magnetic polarization of the oxygen 2p band. We evaluate these contributions in the local-spin-density approximation and argue that they play a very important role in stability of the FM ground state in CrO2.

Author keywords:

TRANSITION-METALS; DOUBLE EXCHANGE; BAND-STRUCTURE; MAGNETIC-INTERACTIONS; DENSITY; APPROXIMATION; MANGANITES; TRANSPORT; SYSTEMS; MODEL

DOI:

10.1103/PhysRevB.92.144407

Web of Science ID:

ISI:000362427900006

Соавторы в МНС:

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Другие поля

Поле	Значение
Month	OCT 7
Publisher	AMER PHYSICAL SOC
Address	ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA
Language	English
Article-Number	144407
EISSN	2469-9969
Keywords-Plus	TRANSITION-METALS; DOUBLE EXCHANGE; BAND-STRUCTURE; MAGNETIC-INTERACTIONS; DENSITY; APPROXIMATION; MANGANITES; TRANSPORT; SYSTEMS; MODEL
Research-Areas	Physics
Web-of-Science-Categories	Physics, Condensed Matter
Author-Email	solovyev.Igor@nims.go.jp
ResearcherID-Numbers	Mazurenko, Vladimir/P-9241-2017 Solovyev, Igor/B-1320-2010
ORCID-Numbers	Solovyev, Igor/0000-0002-2010-9877
Funding-Acknowledgement	Russian Science Foundation {[}14-12-00306]
Funding-Text	This work is partly supported by a grant from Russian Science Foundation (Project No. 14-12-00306).
Number-of-Cited-References	67
Usage-Count-Last-180-days	6
Usage-Count-Since-2013	43
Journal-ISO	Phys. Rev. B
Doc-Delivery-Number	CS9RD