Epitaxial integration of ferromagnetic correlated oxide LaCoO3 with Si (100)

Abstract

We have grown epitaxial strained LaCoO3 on (100)-oriented silicon by molecular beam epitaxy using a relaxed epitaxial SrTiO3 buffer layer. Superconducting quantum interference device magnetization measurements show that, unlike the bulk material, the ground state of the strained LaCoO3 on silicon is ferromagnetic with a TC of 85 K. First principles calculations suggest that a ferromagnetic ground state can be stabilized in LaCoO3 by a sufficiently large biaxial tensile strain with the transition accompanied by a partial untilting of the CoO6 octahedra.

Strain-driven spin-state transition and superexchange interaction in LaCoO3:Abinitiostudy

“…While a substantial body of experimental results for strained LCO has been reported, there is a clear lack of theoretical understanding taking into account all the experimental observations [10,[26][27][28]. Using density functional theory (DFT), Gupta et al, have claimed that tensile strain is able to stabilize a FM ground state in LCO [26] while Rondinelli et al, have suggested that strain by itself cannot produce a FM state [27].…”

“…In this article, using first-principles calculations, we expand our previous theoretical work on strained LCO [10] by considering homogeneous IS states and inhomogeneous HS/LS mixed states as a function of biaxial strain from -4% to 4%. We show that beyond a tensile strain of 2.5%, LCO undergoes a spin state transition from LS to mixed HS/LS states [13], and also explain why the higher concentration of HS Co 3+ is preferred in tensile-strained LCO [6].…”

“…Though LCO is a classic example of a correlated 3d transition metal perovskite oxide [15,16], FM correlation has never been observed for the bulk ground state where the Co 3+ ions exist in the so-called low spin (LS) state (total spin per Co S=0) [15]. Since the first demonstration by Fuchs et al using films grown by pulsed laser deposition (PLD) [5] and by our group using molecular beam epitaxy (MBE) [10], several intriguing properties of strained LCO have been found experimentally. In addition to transport measurements showing insulating behavior for tensile-strained FM LCO [7], Fuchs and co-workers have also shown that both the population of higher spin states and the magnetization in LCO increase as tensile strain increases [6].…”

“…Furthermore, strain engineering in these oxide heterostructures opens up routes for creating novel electronic phases [2][3][4]. An exciting example is the recent demonstration of biaxial tensile strain stabilizing an insulating ferromagnetic (FM) ground state in LaCoO 3 (LCO) [5][6][7][8][9][10][11][12][13][14]. Though LCO is a classic example of a correlated 3d transition metal perovskite oxide [15,16], FM correlation has never been observed for the bulk ground state where the Co 3+ ions exist in the so-called low spin (LS) state (total spin per Co S=0) [15].…”

“…In our previous work, using local spin density approximation combined with the Hubbard U correction (LSDA+U), we have shown that a ferromagnetic state based on a homogenous intermediate spin (IS) state (S=1) can be stabilized above 3.8% tensile strain [10]. The ferromagnetic IS state is, however, inconsistent with two experimentally determined properties of strained LCO: the IS state is half-metallic while experiment shows that strained LCO is insulating [7], and a rather high critical strain of 3.8% is required, which is somewhat higher than that in experiment (~2%) [5][6][7][8][9][10]. Most recently, using a LDA+U approach, Hsu et al have shown that a HS/LS mixed state has a lower energy than that of the IS state in tensile-strained LCO on STO [28].…”