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Capping layers and their roles in polar catastrophe scenario of LaAlO3/SrTiO3 (001) systems
Cho Jinhyung,Jeen Hyoungjeen 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.10
Under the assumption that epitaxially strained growth is taking place under strained growth conditions, the metallic and insulating properties of LaAlO3 (LAO) flms grown on TiO2-terminated SrTiO3 (STO) (001) substrates are theoretically investigated in this study. We studied the electronic properties LaAlO3/SrTiO3 flms grown on the periodic superstructure of √2 × √2 in-plane squares of STO substrate to accommodate the structural strain of heterogeneous flm by allowing tilting of octahedra, as well as distortion. This enables us to study electronic and structural properties by allowing structural relaxation in a more realistic manner. This study examined spin-polarized Ti density functional calculations which promote metal–insulator transition toward thinner LAO/STO than in cases without spin polarization. Using the density of states at the Fermi level obtained from fully relaxed structures, the study shows that a capping layer of LaAlO3, Al2O3, and La2O3 on top of a stoichiometric AlO2 layer promotes toward-metallic transition, causing thin LAO flms to undergo metallic transitions sooner than stoichiometric LAO flms to do so.
Mickel, Patrick R.,Jeen, Hyoungjeen,Kumar, Pradeep,Biswas, Amlan,Hebard, Arthur F. American Physical Society 2016 Physical Review B Vol.93 No.13
<P>We report a giant linear magnetoelectric coupling in strained BiMnO3 thin films in which the disorder associated with an islanded morphology gives rise to extrinsic relaxor ferroelectricity that is not present in bulk centrosymmetric ferromagnetic crystalline BiMnO3. Strain associated with the disorder is treated as a local variable, which couples to the two ferroic order parameters, magnetization (M) over right arrow and polarization (P) over right arrow. A straightforward 'gas under a piston' thermodynamic treatment explains the observed correlated temperature dependencies of the product of susceptibilities and the magnetoelectric coefficient together with the enhancement of the coupling by the proximity of the ferroic transition temperatures close to the relaxor freezing temperature. Our interpretation is based on a trilinear coupling term in the free energy of the form (L) over right arrow . ((P) over right arrow x (M) over right arrow), where (L) over right arrow is a hidden antiferromagnetic order parameter, previously postulated by theory for BiMnO3. This phenomenological invariant not only preserves inversion and time-reversal symmetry of the strain-induced interactions but also explains the pronounced linear magnetoelectric coupling without using the more conventional higher order biquadratic interaction proportional to ((P) over right arrow . (M) over right arrow)(2).</P>
Mechanical stability of ferrimagnetic CoFe2O4 flexible thin films
오광림,곽영민,공다솔,류상균,Kim Hyuntae,Jeen Hyoungjeen,최수봉,정종훈 한국물리학회 2021 Current Applied Physics Vol.31 No.-
We fabricated high-quality ferrimagnetic CoFe2O4 (CFO) thin films on a mica substrate using a pulsed laser deposition technique. High-resolution X-ray diffraction and transmission electron microscopy revealed that the film grew epitaxially with the relationships of CFO <1-10> || Mica [010] and CFO [111] || Mica [001]. The films were highly flexible in terms of both inward and outward bending, and exhibited clear ferrimagnetic hysteresis with weak anisotropy in both the in-plane and out-of-plane directions. We observed that the magnetization of CFO films was robust against mechanical stimuli without microcracks. The remnant magnetization and coercive field were within 8% and 11% over a strain of ±0.54%. As the number of bending cycles increased, the magnetic easy axis became more closely aligned to the out-of-plane direction, without any noticeable change in domain size.