Many-body Green's function theory for the magnetic reorientation of thin ferromagnetic films

Fröbrich, P.; Jensen, P. J.; Kuntz, P. J.; Ecker, A.

doi:10.1007/s100510070005

Cited by 95 publications

(246 citation statements)

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“…This is not the case when using, as we did in Refs. [3] and [5] and we do in the present paper, an approximate decoupling on the level of the lowest-order Green's functions proposed by Anderson and Callen [6], which however is only a good approximation for small anisotropies, as we showed in Ref. [7] by comparing with 'exact' Quantum Monte Carlo calculations.…”

Section: Introductionsupporting

confidence: 54%

“…This was done in Ref. [8] for the case of spin S = 1 and an out-of-plane single-ion anisotropy by using the commutator Green's functions. In order to obtain sufficient equations it was necessary, to add equations coming from the condition that the commutator Green's functions have to be regular at ω = 0, which we call the regularity conditions.…”

Section: The Model and The Green's Function Formalismmentioning

confidence: 99%

“…In both papers an exchange anisotropy was used, because it is easier to treat than the single-ion anisotropy. In connection with the reorientation of the magnetization of a ferromagnetic film (with an out-of-plane anisotropy) as function of the temperature and film thickness we have already discussed similarities and differences between single-ion and exchange anisotropies [3]. In the latter paper the magnetic dipole-dipole interaction was also included.…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic susceptibilities of thin ferromagnetic films within many-body Green function theory: single-ion anisotropy versus exchange anisotropy

Fröbrich¹,

Kuntz²

2004

J. Phys.: Condens. Matter

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Abstract. We compare transverse and parallel static susceptibilities of in-plane uniaxial anisotropic ferromagnetic Heisenberg films calculated in the framework of many-body Green's function theory using single-ion anisotropies with the previously investigated case of exchange anisotropies. On the basis of the calculated observables (easy and hard axes magnetizations and susceptibilities) no significant differences are found, i.e. it is not possible to propose an experiment that might decide which kind of anisotropy is acting in an actual ferromagnetic film.

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Section: Introductionsupporting

confidence: 54%

Section: The Model and The Green's Function Formalismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Anisotropic susceptibilities of thin ferromagnetic films within many-body Green function theory: single-ion anisotropy versus exchange anisotropy

Fröbrich¹,

Kuntz²

2004

J. Phys.: Condens. Matter

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“…For instance, the Holstein-Primakoff approach has been applied frequently [13,14], which is valid for low tem-2 peratures. On the other hand, the Green's function method [15][16][17] and the Schwinger-Boson approximations [18,19] can be used also at higher temperatures, since they consider partly interactions between spin-waves. The Green's function method is a hierachical approach, i.e.…”

mentioning

confidence: 99%

“…Note also that single-ion anisotropy terms can be replaced by irreducible tensor operators [10,12,20,21]. Furthermore, the investigation of the magnetic properties within a Green's function theory can be facilitated [14][15][16][17]. For instance, the higher order Green's functions appearing in the equation of motion can be replaced by lower order ones without approximation, if the involved local spin operators are reduced along the lines described here.…”

mentioning

confidence: 99%

Theory for the reduction of products of spin operators

Jensen

Aguilera‐Granja

2000

Physics Letters A

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In this study we show that the sum of the powers of arbitrary products of quantum spin operators such as (S + ) l (S − ) m (S z ) n can be reduced by one unit, if this sum is equal to 2S + 1, S being the spin quantum number. We emphasize that by a repeated application of this procedure all arbitrary spin operator products with a sum of powers larger than 2S can be replaced by a combination of spin operators with a maximum sum of powers not larger than 2S. This transformation is exact. All spin operators must belong to the same lattice site. By use of this procedure the consideration of singleion anisotropies and the investigation of the magnetic reorientation within a Green's function theory are facilitated. Furthermore, it may be useful for the study of time dependent magnetic properties within the ultrashort (fsec) time domain.

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Many-body Green's function theory for thin ferromagnetic films: exact treatment of the single-ion anisotropy

Froebrich¹,

Kuntz²,

Saber³

2002

Ann. Phys.

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A theory for the magnetization of ferromagnetic films is formulated within the framework of many-body Green's function theory which considers all components of the magnetization. The model Hamiltonian includes a Heisenberg term, an external magnetic field, a second-and fourth-order uniaxial single-ion anisotropy, and the magnetic dipole-dipole coupling. The single-ion anisotropy terms can be treated exactly by introducing higher-order Green's functions and subsequently taking advantage of relations between products of spin operators which leads to an automatic closure of the hierarchy of the equations of motion for the Green's functions with respect to the anisotropy terms. This is an improvement on the method of our previous work, which treated the corresponding terms only approximately by decoupling them at the level of the lowest-order Green's functions. RPA-like approximations are used to decouple the exchange interaction terms in both the low-order and higher-order Green's functions. As a first numerical example we apply the theory to a monolayer for spin S = 1 in order to demonstrate the superiority of the present treatment of the anisotropy terms over the previous approximate decouplings.

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Many-body Green's function theory for the magnetic reorientation of thin ferromagnetic films

Cited by 95 publications

References 1 publication

Anisotropic susceptibilities of thin ferromagnetic films within many-body Green function theory: single-ion anisotropy versus exchange anisotropy

Anisotropic susceptibilities of thin ferromagnetic films within many-body Green function theory: single-ion anisotropy versus exchange anisotropy

Theory for the reduction of products of spin operators

Many-body Green's function theory for thin ferromagnetic films: exact treatment of the single-ion anisotropy

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