Abstract
This work relates to the integration of the two-layer stack of the proposed multiferroic structure onto silicon substrates. Ba1-xSrxTiO3 is an excellent material for room-temperature voltage-tunable dielectric applications due to its high (ε=6000) dielectric constant. In this study we choose a composition of Ba0.4Sr0.6TiO3 (BST), which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (TC) at 200K. The main focus of the present work is to study what happens when BST is placed in contact with a room temperature ferromagnetic layer such as La0.7Sr0.3MnO3 (LSMO). In this study, the magnetic properties of a BST (200nm)/LSMO (63nm) heterostructure was compared to that of a single LSMO layer (63nm). Both films were deposited onto MgO/TiN buffered Si (100) using pulsed laser deposition (PLD) and a domain matching epitaxy (DME) paradigm. X-ray diffraction (XRD) measurements showed that these films were of single phase and epitaxial in nature, with an unrelaxed lattice strain of ∼0.2% that was predominately composed of thermal and defect-induced strain. The magnetic measurements showed that the Curie temperature (TC) of LSMO remained unchanged at 350K when the BST was in contact with the LSMO layer. Interestingly, at 4K both the coercive field (Hc) and the exchange bias (HEB) of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature.
Highlights
Previous workers[1,2,3,4,5,6,7] have deposited BST thin films on oxide substrates such as MgO, LaAlO3, SrTiO3, and Al2O3
The temperature- and magnetic field-dependent measurements performed show that the Curie temperature (TC) for the LSMO and BST/LSMO samples remain constant at 350K, while the coercive field (Hc) and the exchange bias (HEB) measured at low temperature (4K) increased significantly from 400 to 800 Oe, and from 155 to 305 Oe, respectively, when BST is placed in contact with the LSMO layer
It should be noted that the epitaxial growth of BST/LSMO/MgO/TiN on Si (100) is possible due to the epitaxial growth of large mismatched system based on the domain matching epitaxy (DME) paradigm,[14,15] e.g., TiN (a = 4.24 A◦) on Si (100) (a = 5.43 A◦) where four lattice constants of TiN match with three of Si (100)
Summary
Previous workers[1,2,3,4,5,6,7] have deposited BST thin films on oxide substrates such as MgO, LaAlO3, SrTiO3, and Al2O3. Si wafers are cheap, available in large dimensions, and are standard substrates in microelectronics It is of great technological as well as scientific interest to integrate BST active thin films with Si substrates. The temperature- and magnetic field-dependent measurements performed show that the Curie temperature (TC) for the LSMO and BST/LSMO samples remain constant at 350K, while the coercive field (Hc) and the exchange bias (HEB) measured at low temperature (4K) increased significantly from 400 to 800 Oe, and from 155 to 305 Oe, respectively, when BST is placed in contact with the (insert) LSMO layer. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer
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