Helimagnetic thin films: Surface reconstruction, surface spin-waves and magnetization

Hog, Sahbi El; Diep, H. T.

doi:10.1016/j.jmmm.2015.08.016

Cited by 15 publications

(10 citation statements)

References 34 publications

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“…Let us mention our previous works on a frustrated surface [15] and on a frustrated FCC antiferromagnetic film [16] where surface spin rearrangements and surface phase transitions have been found. We have also recently shown results in zero field of thin films of body-centered cubic (BCC) and simple cubic (SC) structures [17,18]. The helical angle along the c axis perpendicular to the film surface was found to strongly vary in the vicinity of the surface.…”

mentioning

confidence: 87%

“…Most of theoretical studies were limited to collinear magnetic orderings. Phase transitions in thin films with non-collinear ground states have been only recently studied [15][16][17][18]25]. MC simulations of a helimagnetic thin film [26] and a few experiments in helimagnets [27,28] have also been carried out.…”

Section: Phase Transitionmentioning

confidence: 99%

“…Note that without an applied field, the spins lie in the xy planes: spins in the same plane are parallel while two NN in the adjacent planes form an angle α which varies with the position of the planes [18], unlike in the bulk. As will be seen below, the applied magnetic field gives a very complex spin configuration across the film thickness.…”

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confidence: 99%

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Partial phase transition and quantum effects in helimagnetic films under an applied magnetic field

Hog

Diep

2017

Journal of Magnetism and Magnetic Materials

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We study the phase transition in a helimagnetic film with Heisenberg spins under an applied magnetic field in the c direction perpendicular to the film. The helical structure is due to the antiferromagnetic interaction between next-nearest neighbors in the c direction. Helimagnetic films in zero field are known to have a strong modification of the in-plane helical angle near the film surfaces. We show that spins react to a moderate applied magnetic field by creating a particular spin configuration along the c axis. With increasing temperature (T ), using Monte Carlo simulations we show that the system undergoes a phase transition triggered by the destruction of the ordering of a number of layers. This partial phase transition is shown to be intimately related to the ground-state spin structure. We show why some layers undergo a phase transition while others do not. The Green's function method for non collinear magnets is also carried out to investigate effects of quantum fluctuations. Non-uniform zero-point spin contractions and a crossover of layer magnetizations at low T are shown and discussed.

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confidence: 87%

Section: Phase Transitionmentioning

confidence: 99%

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Partial phase transition and quantum effects in helimagnetic films under an applied magnetic field

Hog

Diep

2017

Journal of Magnetism and Magnetic Materials

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“…( 7). M depends strongly on J mf : at high T, larger J mf yields stronger M. However, at T = 0 the spin length is smaller for larger θ due to the so-called spin contraction in antiferromagnets [17]. As a consequence there is a crossover of magnetizations with different θ at low T as shown in Fig.…”

Section: F T T D K E K E F I J Xymentioning

confidence: 93%

Elementary excitations in anisotropic nanofilms of multiferroics with competing interactions at the interface

Sharafullin

Diep²

2020

Lett. Mater.

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In this work we study, using the of two-time Green's functions method, the spectrum of spin waves in a monolayer and bilayer of anisotropic magnetic film sandwiched between the ferroelectric layers in a magnetoelectric superlattice. Surface spin configuration is calculated by minimizing the interaction energy. It is shown that the angles between spins near the surface are strongly modified with respect to the bulk configuration. We include the anisotropy energy between the spin vectors at sites i and j in the Hamiltonian of multiferroic superlattice. The anisotropy energy stabilizes the angle between local quantization axes. The anisotropy parameter K i,j supposed positive, and nonzero only for the nearest interacting neighbors. It is shown that the magnetoelectric interaction strongly affects the long-wavelength mode of spin waves. The magnetization of the magnetic film at low temperatures was also calculated. The magnetization M is strongly dependent on temperatures: at higher T, the larger the magnetoelectric interaction, the greater is M. However, at T = 0, the spin length becomes smaller for large values of the magnetoelectric interaction due to the so-called spin reduction that takes place in antiferromagnets. As a result, the crossover (intersection) of the magnetization curves occurs for different values of θ at low T.

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“…We have recently used the Green’s function method and Monte Carlo simulations to study helimagnetic films in zero field [ 63 , 78 ] and in a perpendicular field [ 79 ]. We summarize here some results and emphasize their importance.…”

Section: Frustrated Thin Films: Surface Phase Transitionmentioning

confidence: 99%

Phase Transition in Frustrated Magnetic Thin Film—Physics at Phase Boundaries

Diep

2019

Entropy

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In this review, I outline some principal theoretical knowledge on the properties of frustrated systems and thin films. The two points I would like to emphasize: i) the physics in low dimensions where exact solutions can be obtained, ii) the physics at phase boundaries where spectacular phenomena can occur due to competing interactions of the two phases around the boundary. This competition causes a frustration. I will concentrate my attention to thin films and phenomena occurring near the boundary of two phases of different symmetries. The case of two-dimensional (2D) systems is in fact the limiting case of thin films with a monolayer. Naturally, I will treat this case at the beginning. After a short introduction on frustrated spin systems, I show several 2D frustrated Ising spin systems which can be exactly solved by using vertex models. These systems contain most of the spectacular effects due to the frustration: high ground-state degeneracy, existence of several phases in the ground-state phase diagram, multiple phase transitions with increasing temperature, reentrance, disorder lines, partial disorder at equilibrium. Evidences of such effects in non solvable models are also shown and discussed. Thin films are next presented with different aspects: surface elementary excitations (surface spin-waves), surface phase transition and criticality. Several examples are shown and discussed. New results on skyrmions in thin films and superlattices are also displayed.

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Helimagnetic thin films: Surface reconstruction, surface spin-waves and magnetization

Cited by 15 publications

References 34 publications

Partial phase transition and quantum effects in helimagnetic films under an applied magnetic field

Partial phase transition and quantum effects in helimagnetic films under an applied magnetic field

Elementary excitations in anisotropic nanofilms of multiferroics with competing interactions at the interface

Phase Transition in Frustrated Magnetic Thin Film—Physics at Phase Boundaries

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