T. Garg

Bio: T. Garg is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Dielectric & Thin film. The author has an hindex of 3, co-authored 7 publications receiving 83 citations. Previous affiliations of T. Garg include VIT University & University of Rochester.

Hysteresis and remanence in magnetoelectric effects in functionally graded magnetostrictive-piezoelectric layered composites

Abstract: The observation and theory of a large remanent magnetoelectric (ME) coefficient and coercivity in the static field $H$ dependence of the low-frequency ME effects are reported for bilayers of lead zirconate titanate (PZT) and a functionally graded ferromagnetic layer. The grading involves magnetization with the use of nickel zinc ferrite of composition Ni${}_{0.7}$Zn${}_{0.3}$Fe${}_{2}$O${}_{4}$ (NZFO) and pure Ni. In homogeneous bilayers of PZT-Ni or PZT-NZFO, the ME voltage coefficient (MEVC) vs $H$ data do not show any hysteresis or remanence. Upon grading the ferromagnetic layer, significant changes including hysteresis and remanece are observed. In PZT-Ni-NZFO, MEVC vs $H$ data show a positive remnant MEVC and a negative coercive field. When the grading is reversed, in samples of PZT-NZFO-Ni, the remnant MEVC is negative and the coercive field is positive. A theory is proposed for the low-frequency ME effects in the graded composites. According to the model, the grading in the magnetization leads to a built-in magnetic field in the ferromagnetic layer, and this field depends on the sequence of grading and the thickness of the NZFO and Ni layers. As a result, the total torque moment and flexural deformations in the composite and the bias field dependence of ME voltage coefficient becomes strongly hysteretic. Calculated MEVC vs $H$, remnant MEVC, and coercive field are in good agreement with the data.

Room-temperature magneto-dielectric response in multiferroic ZnFe2O4/PMN-PT bilayer thin films

Abstract: The magneto-dielectric response in multiferroic ZnFe2O4/PMN-PT bilayer thin films prepared on a glass substrate using RF magnetron sputtering has been investigated in this work. PMN-PT thin films (i.e. PMN-PT/LCMO/Pt/Ti/glass) deposited on glass were used as a substrate for deposition of ZnFe2O4 thin films. ZnFe2O4 thin films were annealed ex situ at different temperatures. Structural, magnetic, ferroelectric, dielectric and magneto-dielectric studies were carried out on these multiferroic bilayer thin films. Structural studies revealed the presence of each layer in its respective single phase. Magnetic and ferroelectric studies revealed the ferromagnetic and ferroelectric behaviors of these bilayers. To quantify the magnetoelectric coupling, the dielectric constant of the bilayer was measured at room temperature as a function of frequency with and without the applied magnetic field. The magneto-dielectric response MD(%) was calculated by finding the relative change in dielectric constant at 1 kHz as a percentage. The observed MD response was correlated with magnetization of the ferrite layer. An MD response of 2.60% was found for a bilayer film annealed at 350 °C. At this particular annealing temperature, the ZnFe2O4 layer also has the highest saturation magnetization of 1900 G.

Influence of PbTiO3 addition on microstructure of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics

Abstract: Synthesis of PMN-PT ceramics has been a challenge due to the undesirable pyrochlore phase formation. We have synthesized PMN-PT ceramics with varying PT content (x = 0.1, 0.15 and 0.3) using columbite precursor method. Influence of PT addition on the perovskite phase formation and microstructure has been studied using X-ray diffraction and scanning electron microscope respectively.

Multiferroic Heterostructures Integrating Ferroelectric and Magnetic Materials.

Abstract: Multiferroic heterostructures can be synthesized by integrating monolithic ferroelectric and magnetic materials, with interfacial coupling between electric polarization and magnetization, through the exchange of elastic, electric, and magnetic energy. Although the nature of the interfaces remains to be unraveled, such cross coupling can be utilized to manipulate the magnetization (or polarization) with an electric (or magnetic) field, known as a converse (or direct) magnetoelectric effect. It can be exploited to significantly improve the performance of or/and add new functionalities to many existing or emerging devices such as memory devices, tunable microwave devices, sensors, etc. The exciting technological potential, along with the rich physical phenomena at the interface, has sparked intensive research on multiferroic heterostructures for more than a decade. Here, we summarize the most recent progresses in the fundamental principles and potential applications of the interface-based magnetoelectric effect in multiferroic heterostructures, and present our perspectives on some key issues that require further study in order to realize their practical device applications.

Understanding and designing magnetoelectric heterostructures guided by computation: progresses, remaining questions, and perspectives

Abstract: Magnetoelectric composites and heterostructures integrate magnetic and dielectric materials to produce new functionalities, e.g., magnetoelectric responses that are absent in each of the constituent materials but emerge through the coupling between magnetic order in the magnetic material and electric order in the dielectric material. The magnetoelectric coupling in these composites and heterostructures is typically achieved through the exchange of magnetic, electric, or/and elastic energy across the interfaces between the different constituent materials, and the coupling effect is measured by the degree of conversion between magnetic and electric energy in the absence of an electric current. The strength of magnetoelectric coupling can be tailored by choosing suited materials for each constituent and by geometrical and microstructural designs. In this article, we discuss recent progresses on the understanding of magnetoelectric coupling mechanisms and the design of magnetoelectric heterostructures guided by theory and computation. We outline a number of unsolved issues concerning magnetoelectric heterostructures. We compile a relatively comprehensive experimental dataset on the magnetoelecric coupling coefficients in both bulk and thin-film magnetoelectric composites and offer a perspective on the data-driven computational design of magnetoelectric composites at the mesoscale microstructure level.

Tunable self-biased magnetoelectric response in homogenous laminates

Abstract: In this study, we demonstrate self-biased magnetoelectric effect in homogenous two-phase magnetostrictive-piezoelectric laminates. Our results illustrate the method for tuning the magnitude of self-bias effect and provide understanding behind the hysteretic changes. We model this phenomenon by considering the magnetization hysteresis with shape-induced demagnetization effect. The self-biased response was found to be directly related to the nature of magnetization and can be tuned by variation in demagnetization state and the resultant differential magnetic flux distribution. These results present significant advancement toward development of AC magnetic field sensor and magnetoelectric composite based on-chip devices by eliminating the need for DC bias.

Self-Biased Magnetoelectric Composites: An Overview and Future Perspectives

Abstract: Abstract Self-biased magnetoelectric (ME) composites, defined as materials that enable large ME coupling under external AC magnetic field in the absence of DC magnetic field, are an interesting, challenging and practical field of research. In comparison to the conventional ME composites, eliminating the need of DC magnetic bias provides great potential towards device miniaturization and development of components for electronics and medical applications. In this review, the current state-of-the-art of the different self-biased structures, their working mechanisms, as well as their main characteristics are summarized. Further, the nature and requirement of the self-biased magnetoelectric response is discussed with respect to the specific applications. Lastly, the remaining challenges as well as future perspective of this research field are discussed.