Electrically tunable materials for microwave applications

Ahmed, Aftab; Goldthorpe, Irene A.; Khandani, Amir K.

doi:10.1063/1.4906255

Cited by 150 publications

(80 citation statements)

References 110 publications

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“…From the 2θ XRD data for the (002) peak, the out-of-plane (OOP) lattice parameters of BST and LSMO layer are determined as 3.956A • and 3.843A • , respectively. These are very close to the bulk lattice parameters of BST (3.965A • ) [1][2][3][4][5][6][7] and LSMO (3.870A • ) 12,13 layers. The estimated strain for BST and LSMO layers along the c-direction is ∼0.2% and 0.7%, respectively, which is attributed to unrelaxed thermal and defect-induced strain, and some additional unrelaxed lattice mismatch strain for the BST (delete LSMO and insert BST) layer grown on the LSMO (delete BST and insert LSMO).…”

Section: Resultssupporting

confidence: 55%

“…The magnetic response is not saturated under a 300 Oe field, hence, it is expressed only in magnetic moment (emu), not in emu/cc. [1][2][3][4][5][6][7] The enhancements in H c and H EB at low temperature appears to be directly related to the ferroelectric nature of BST layer, and the resulting strain (∼0.4%) and/or charge redistributions that take place as the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature (200K). 18 This may also be consistent with the number of previous reports [19][20][21][22] on the formation of an antiferromagnetic region or layer due to strong pinned spins and magnetic depletion layer observed at various ferromagnetic and ferroelectric interfaces.…”

Section: Fig 2 Magnetic Moment Vs Temperature (M-t) Curves Of Lsmomentioning

confidence: 99%

“…For this study a concentration of Ba 0.4 Sr 0.6 TiO 3 (BST) is chosen, which is cubic and paraelectric at the (delete) ambient temperature, and then transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (T C ) at 200K. 4 Previous workers [1][2][3][4][5][6][7] have deposited BST thin films on oxide substrates such as MgO, LaAlO 3 , SrTiO 3 , and Al 2 O 3 . However, high single crystal cost and small size are their (delete) major drawbacks of such substrates.…”

Section: Introductionmentioning

confidence: 99%

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Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

2017

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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.

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Section: Resultssupporting

confidence: 55%

Section: Fig 2 Magnetic Moment Vs Temperature (M-t) Curves Of Lsmomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

2017

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“…Tunability can be achieved in a number of ways, including (i) electrical tuning of permittivity, (ii) electrical tuning of permeability, (iii) magnetic tuning of permittivity, and (iv) magnetic tuning of permeability, as well as simultaneous tuning of both permittivity and permeability [55,56]. These changes can be achieved by adjusting the geometry of the unit-cell, for example, size, orientation, and position of resonators, or the material of the substrate.…”

Section: Tunable Metamaterialsmentioning

confidence: 99%

Metamaterials for Microwave Radomes and the Concept of a Metaradome: Review of the Literature

Özis

Osipov

Eibert

2017

International Journal of Antennas and Propagation

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A radome is an integral part of almost every antenna system, protecting antennas and antenna electronics from hostile exterior conditions (humidity, heat, cold, etc.) and nearby personnel from rotating mechanical parts of antennas and streamlining antennas to reduce aerodynamic drag and to conceal antennas from public view. Metamaterials are artificial materials with a great potential for antenna design, and many studies explore applications of metamaterials to antennas but just a few to the design of radomes. This paper discusses the possibilities that metamaterials open up in the design of microwave radomes and introduces the concept of metaradomes. The use of metamaterials can improve or correct characteristics (gain, directivity, and bandwidth) of the enclosed antenna and add new features, like band-pass frequency behavior, polarization transformations, the ability to be switched on/off, and so forth. Examples of applications of metamaterials in the design of microwave radomes available in the literature as well as potential applications, advantages, drawbacks, and still open problems are described.

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“…Up to now, only ferromagnetic, ferroelectric, and liquid crystals have conferred an inherent tunability of the microwave devices. 17 However, in the microwave range, the surface resistance is, in principle, greater than a few hundreds of ohms when no bias is applied, which is a detrimental effect implying losses and moderate radiation efficiencies.…”

mentioning

confidence: 99%