Magnetic ordering anisotropy in epitaxial orthorhombic multiferroic YMnO3 films

Abstract

Orthorhombic YMnO3 thin films with (200), (020), and (001) orientations were, respectively, obtained by pulsed laser deposition on SrTiO3(110), LaAlO3(110), and SrTiO3(001) substrates. The results demonstrate that the strain between film and substrate can serve as an alternative in transforming the thermodynamically stable hexagonal YMnO3 into the orthorhombic phase, which previously could be obtained with high-pressure high temperature syntheses and epitaxy-stabilized thin film processes. More importantly, these films allow us, for the first time, to unambiguously disclose the intrinsic magnetic property along different crystallographic orientations. Our results show that, although the antiferromagnetic (AFM) ordering remains the same, there is an additional spin reordering transition which is very much dependent on the crystallographic orientation along which the measuring field was applied and on the in-plane crystallographic alignment of the films. Detailed analyses indicate that the origin of the observed second reordering may be due to some strain-induced canted AFM state instead of the incommensurate lock-in transitions conceived previously.

Magnetism-induced ferroelectric polarization in the c-axis-oriented orthorhombic HoMnO3 thin films

“…As a result, alternative ways of preparing orientation-specific orthorhombic RMnO 3 thin films have received extensive attention lately. 8,[14][15][16][17][18] Very recently, consistent with those reported on bulk o-HMO samples, 6,10 we have observed a distinct peak in the temperature dependence of the dielectric constant in the c-axis-oriented o-HMO films at temperatures near the spinreorientation transition of Ho. 16 Similar observations were reported subsequently in the a-axis-oriented o-HMO films.…”

Strain tuned magnetoelectric coupling in orthorhombic YMnO3 thin films

“…[8][9][10] Besides, the unexpected observation of ferromagnetism in thin films, otherwise antiferromagnetic in bulk, has focussed more attention. 8,9,[11][12][13][14] Our recent results on orthorhombic YMnO 3 indicate that the ferromagnetic behavior increases with the unit cell distortion. 14 However, the analysis of the impact of the lattice distortion on the dielectric properties in thin films has remained unrevealed.…”

“…1͑a͒ and 2͑a͒ increases as the unit cell is more distorted 14 and can be described as a straininduced canting of the Mn magnetic moment. 11,14 Therefore, even in the absence of magnetic field, the spontaneous noncollinear magnetic order is expected to resound in the dielectric properties. Fig.…”

Emergence of ferromagnetism in antiferromagnetic TbMnO3 by epitaxial strain

“…9-17͒ revealed the unexpected existence of a ferromagnetic response in otherwise bulk antiferromagnetic materials. Whereas in the case of E-type spin-ordered structures, its origin has been attributed to strain-induced deformation of the unit cell and subsequent unbalancing of magnetic interactions, [9][10][11][12]17 it also has been proposed domain walls boundaries to be relevant in the case of the spiral TbMnO 3 . 16 However, it turns out that the signatures of ferromagnetism reported 9-17 are in all cases intriguingly similar.…”

“…Whereas in the case of E-type spin-ordered structures, its origin has been attributed to strain-induced deformation of the unit cell and subsequent unbalancing of magnetic interactions, [9][10][11][12]17 it also has been proposed domain walls boundaries to be relevant in the case of the spiral TbMnO 3 . 16 However, it turns out that the signatures of ferromagnetism reported [9][10][11][12][13][14][15][16][17] are in all cases intriguingly similar. Whether the origin of the ferromagnetism in both compounds is the same irrespective of their bulk magnetic structure is a critical open issue that we aim to disentangle in this paper.…”