An inverse transition of magnetic domain patterns in ultrathin films

Abstract

Inverse freezing and inverse melting are processes where a more symmetric phase is found at lower temperatures than at higher temperatures. Such inverse transitions are very rare. Here we report the existence of an inverse transition effect in ultrathin Fe films that are magnetized perpendicular to the film plane. The magnetization of these films is not uniform, but instead manifests itself as stripe domains with opposite perpendicular magnetization. Predictions relating to the disordering of this striped ground state in the limit of monolayer film thicknesses are controversial. Mean-field arguments predict a continuous reduction of the stripe width when the temperature is increased; other studies suggest that topological defects, such as dislocations and disclinations, might penetrate the system and induce geometrical phase transitions. We find, from scanning electron microscopy imaging, that when the temperature is increased, the low-temperature stripe domain structure transforms into a more symmetric, labyrinthine structure. However, at even higher temperatures and before the loss of magnetic order, a re-occurrence of the less symmetric stripe phase is found. Despite the widespread theoretical and experimental work on striped systems, this phase sequence and the microscopic instabilities driving it have not been observed before.

Patterns close to the critical field in type-I superconductors

“…Similar behavior is observed in ferrimagnetic garnet films. 20 Besides branching of domains, breaking of some stripes is also observed, see Figs. 3͑a͒ and 3͑b͒.…”

Dipolar-energy-activated magnetic domain pattern transformation driven by thermal fluctuations

“…In the particular case studied heremagnetic domain patterns in ultra thin ferromagnetic films-the basis for pattern formation is the interplay between various magnetic energies where the ratio between uniaxial anisotropy, dipolar and exchange interaction plays the decisive role. Magnetic domain patterns in perpendicularly magnetized ultra thin films are typically characterized by the geometric shape of the domains, such as labyrinth, stripe, bubble or simply disordered patterns [1][2][3][4][5] . According to theory and experiments, these patterns appear in distinct sequences as a function of temperature or film thickness.…”

Controlled nucleation of topological defects in the stripe domain patterns of lateral multilayers with perpendicular magnetic anisotropy

“…Amorphous 80-nm NdCo 5 alloy films have been grown by cosputtering from pure Nd and Co targets on 10-nm Al/Si(100) substrates, and protected from oxidation with a 3-nm Al capping layer. 36 At room temperature, the saturation magnetization is M s = 1100 emu/cm 3 and the perpendicular anisotropy constant is K N ≈ 10 6 erg/cm 3 , 36 so that Q = K N /2πM 2 s ≈ 0.18 implying that the Nd-Co films can be considered within the weak PMA regime.…”

“…These topological defects play an important role in magnetization reversal processes and magnetization dynamics of PMA materials [12][13][14] and, also, in the physics of phase transitions in 2D modulated phases. 5,15 However, the experimental study of these topological defects in PMA materials has been hindered by the problems to control their nucleation in extended samples since they usually occur within very disordered labyrinthine configurations.…”

“…1,2 The actual domain pattern in a given PMA film can be very complex depending on material parameters, sample geometry, and magnetic and thermal history, [3][4][5] but a simple description of disordered stripe patterns can be achieved if the concept of topological defects within the two-dimensional (2D) periodic stripe magnetic structure is used. 6,7 Defects such as dislocations, 8 disclinations, 7 grain boundaries, 9 or even skyrmions 10,11 have been observed.…”