Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO₃thin films

Abstract

We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO(3) (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO(3)(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho(3+) moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c-axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.

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.…”

Microstructure and strain relaxation of orthorhombic TmMnO3 epitaxial thin films

“…Epitaxial stabilization of this orthorhombic phase in thin films were achieved by metal-organic chemical vapor deposition (MOCVD) [3] and pulsed laser deposition (PLD) [4][5][6]. Meanwhile, recent studies have reported the strain-induced effects on ferroelectricity [7], magnetic ordering [8], magnetocapacitance [9], and magnetoelectric coupling [10] in o-RMnO 3 thin films. Large electric polarization and magnetoelectric coupling have just been found in o-TmMnO 3 (o-TMO) thin films [6].…”

Abnormal magnetic ordering and ferromagnetism in perovskite ScMnO3 film

“…In addition, the difference between the formation energies of the orthorhombic and the hexagonal RMnO 3 phases could be small, so it might be possible to prepare the orthorhombic phase from the hexagonal phase through epitaxial thin-film growth, such as orthorhombic HoMnO 3 thin film. [18][19][20][21] However, due to contributions from both Mn 3þ and magnetic Ho 3þ , the low-temperature magnetic property and the origin of ferroelectric polarization in orthorhombic HoMnO 3 bulk/thin film become more complex. Since Sc 3þ in ScMnO 3 has no localized magnetic moment, the lowtemperature magnetic property becomes relatively simple.…”

“…In all reported orthorhombic HoMnO 3 and LuMnO 3 films, irrespective of crystal axis direction, the antiferromagnetic ordering temperature is around 40 K and is extremely resistant to lattice strain. [18][19][20][21] Whether the second magnetic transition (or spin reorientation transition of Mn 3þ ) shows up or not and in which crystal direction it appears depend on many factors such as film growth orientation, lattice strain, or R ion size. For example, when (101) orientation orthorhombic HoMnO 3 film grown on Nb-doped SrTiO 3 (111) substrates, 21 no second magnetic transition of Mn 3þ is observed, while in the c-axis orientation orthorhombic HoMnO 3 film grown on Nb-doped SrTiO 3 (001), 18 a second magnetic transition shows up.…”