Hidden magnetic states emergent under electric field, in a room temperature composite magnetoelectric multiferroic

The ability to control a magnetic phase with an electric field is of great current interest for a variety of low power electronics in which the magnetic state is used either for information storage or logic operations. Over the past several years, there has been a considerable amount of research on pathways to control the direction of magnetization with an electric field. More recently, an alternative pathway involving the change of the magnetic state (ferromagnet to antiferromagnet) has been proposed. In this paper, we demonstrate electric field control of the Anomalous Hall Transport in a metamagnetic FeRh thin film, accompanying an antiferromagnet (AFM) to ferromagnet (FM) phase transition. This approach provides us with a pathway to "hide" or "reveal" a given ferromagnetic region at zero magnetic field. By converting the AFM phase into the FM phase, the stray field, and hence sensitivity to external fields, is decreased or eliminated. Using detailed structural analyses of FeRh films of varying crystalline quality and chemical order, we relate the direct nanoscale origins of this memory effect to site disorder as well as variations of the net magnetic anisotropy of FM nuclei. Our work opens pathways toward a new generation of antiferromagnetic - ferromagnetic interactions for spintronics

TiNi-based thin films for MEMS applications

In this paper, some critical issues and problems in the development of TiNi thin films were discussed, including preparation and characterization considerations, residual stress and adhesion, frequency improvement, fatigue and stability, as well as functionally graded or composite thin film design. Different types of MEMS applications were reviewed and the prospects for future advances in fabrication process and device development were discussed.Singapore-MIT Alliance (SMA

Biasing Effects in Ferroic Materials

In this chapter we present an overview of some important concepts related to the processes and microstructural mechanisms that produce the deformation of hysteresis loops and the loss of their symmetry characteristics in ferroelectric, ferroelastic and ferromagnetic systems. The most discussed themes include: aging and fatigue as primary mechanisms of biased hysteresis loops in ferroelectric/ferroelastic materials, imprint phenomenon as an important biasing process in ferroelectric thin films, the development of an exchange bias field and of specific spin states, such as spin canting and spin-glass-like phases, as the main causes of biased hysteresis loops in different types of magnetic heterostructures. The present discussion leads to the identification of the main differences and possible analogies in the underlying mechanisms of possible biasing effects occurring in the different ferroic systems, which can benefit the theoretical description, modelling, and engineering of multifunctional devices based on ferroic systems experiencing the internal bias phenomena

Coupling of strain and magnetism in manganite-based complex oxide heterostructures

Complex oxide thin films and heterostructures offer a wide range of properties originating from the intrinsic coupling between lattice strain and magnetic/electronic ordering. This article reviews experimental, phenomenological, and theoretical analyses of the coupling of strain with electronic and magnetic properties of mixed valence manganite heterostructures. The influence of epitaxial strain on the magnetic properties of manganite films is measured using macroscopic magnetization measurements and shown mixed reports suggesting, both, an increase and decrease in ferromagnetic phases on the application of the strain. Using polarized neutron reflectivity (PNR), a simultaneous measurement of transport and magnetic properties of manganite thin films showed direct evidence of modification in the magnetic properties on the application of bending strain. The coupling coefficient of strain and magnetism of manganite heterostructures was estimated using PNR, which not only helped to understand the correlation of elastic strain with magnetism but also explained the condition of magnetic phase order change in the phase-separated systems within a phenomenological Ginzburg Landau theory. An overview is also provided of the current perspectives and existing studies on the influence of strain on structure, electronic, magnetic, magnetic anisotropy, phase coexistence and magnetocaloric properties of mixed valence manganite heterostructures. Based on the understanding of a diverse range of perovskite functionalities, detailed perspectives on how the coupling of strain and magnetism open up pathways toward the emergence of novel device design features including the different ways of applying uniform strain, are discussed.Comment: arXiv admin note: text overlap with arXiv:1509.00912, arXiv:1009.4548 by other author

Multiferroics In Perovskite and Aurivillius Structured Materials

PhD thesisMultiferroics (MF) are types of novel materials that possess two- or three- of the so called ‘ferroic’ properties, including ferroelectricity, ferromagnetism and ferroelasticity, which have recently simulated vast number of research activities. Specifically, the couplings between ferroelectricity and ferromagnetism provide the possibilities to create new generation multifunctional devices such as “electric-write, magnetic-read” high density memory media, electric field tunable targeting therapy, micro-magnetic field detection gyro-sensors, etc. There are two main types of materials to realize the multiferroicity, including multiferroics composites and multiferroics single phase compounds. The multiferroics composites, composed by ferromagnetic and ferroelectric phase, are famous for yielding large magnetoelectric (ME) coupling effects above room temperature. However, the multiferroics composites are restricted for applications because their ME coupling effects are commonly achieved by the interaction between piezoelectricity and magnetostriction. The macroscopical couplings are only effective at low frequency range of electric and magnetic fields (below GHz level) and insensitive for low external magnetic fields, which restricts their applications. For the single phase room temperature multiferroics materials, they possibly possess intrinsic ME coupling effects that the magnetic and electric interact mutually through the changes of electron spin. That means the single phase multiferroics are possible to build intrinsic multiferroics for the high speed read/write memory media and low magnetic field detector devices. This study l mainly focus on the preparation, characterization and study on the Aurivillius and perovskite structure based single phase ferroelectric and multiferroics ceramics. The materials in this work were built based on the recent interesting ferroelectric systems including Ba2Bi4Ti5O18, Na0.5Bi0.5TiO3 and x(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-(1-x)BiFeO3. Characterizations on crystal structures, ferroelectric domain structures, dielectric and ferroelectric properties and magnetic properties are intensively investigated and discussed for each composition. For textured Ba2Bi4Ti5O18 ceramics, their dielectric relaxation behaviour has been proved by the diffusion behaviour of dielectric permittivity peaks around Tm (dielectric maxima). Additionally, the other fascinating finding is the electric field induced phase transition behaviour between strong polar-nano-regions (PNRs) to weak PNRs , which is manifested by the current-electric field loops with four peaks on the in-plane and out-of-plane measurement directions. Multiferroics (MF) are types of novel materials that possess two-or three-of the so called ‘ferroic’ properties, including ferroelectricity, ferromagnetism and ferroelasticity, which have recently simulated vast number of research activities. Specifically, the couplings between ferroelectricity and ferromagnetism provide the possibilities to create new generation multifunctional devices such as “electric-write, magnetic-read” high density memory media, electric field tunable targeting therapy, micro-magnetic field detection gyro-sensors, etc. There are two main types of materials to realize the multiferroicity, including multiferroics composites and multiferroics single phase compounds. The multiferroics composites, composed by ferromagnetic and ferroelectric phase, are famous for yielding large magnetoelectric (ME) coupling effects above room temperature. However, the multiferroics composites are restricted for applications because their ME coupling effects are commonly achieved by the interaction between piezoelectricity and magnetostriction. The macroscopical couplings are only effective at low frequency range of electric and magnetic fields (below GHz level) and insensitive for low external magnetic fields, which restricts their applications. For the single phase room temperature multiferroics materials, they possibly possess intrinsic ME coupling effects that the magnetic and electric interact mutually through the changes of electron spin. That means the single phase multiferroics are possible to build intrinsic multiferroics for the high speed read/write memory media and low magnetic field detector devices. This study I mainly focus on the preparation, characterization and study on the Aurivillius and perovskite structure based single phase ferroelectric and multiferroics ceramics. The materials in this work were built based on the recent interesting ferroelectric systems including Ba2Bi4Ti5O18, Na0.5Bi0.5TiO3 and x(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-(1-x)BiFeO3. Characterizations on crystal structures, ferroelectric domain structures, dielectric and ferroelectric properties and magnetic properties are intensively investigated and discussed for each composition. For textured Ba2Bi4Ti5O18 ceramics, their dielectric relaxation behaviour has been proved by the diffusion behaviour of dielectric permittivity peaks around Tm (dielectric maxima). Additionally, the other fascinating finding is the electric field induced phase transition behaviour between strong polar-nano-regions (PNRs) to weak PNRs , which is manifested by the current-electric field loops with four peaks on the in-plane and out-of-plane measurement directions. For Na0.5Bi0.5Ti0.8Mn0.2O3 with Nb additive ceramics, its single phase ceramic has been successfully prepared. In terms of it magnetic nature, the low temperature (< 30 K) remnant magnetization of the M-H loops, the zero-field cooling and field cooling (ZFC-FC) results indicate that the ceramic of Na0.5Bi0.5Ti0.8Mn0.2O3 with Nb additive possesses the low temperature ferromagnetic nature. The suggested Tc for ferromagnetic-paramagnetic phase transition is around 50 K. The research of room-temperature multiferrocity on this single phase ceramic reveals that the BNT based multiferroic is a valuable research direction for the new generation of magnetic-electric coupling devices. For 0.5(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.5BiFe0.8Mn0.2O3 ceramics, the single phase ceramic was successfully prepared. The visible magnetic field tuneable ferroelectric domain switching behaviour under PFM observation present its room temperature magneto-electric coupling effect, which is rarely presented among multiferroics researches. Moreover, the room-temperature ferromagnetism was also strongly confirmed by the apparent remnant magnetization in M-H loops, along with the ZFC-FC results, which indicates that 0.5(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.5BiFe0.8Mn0.2O3 possesses the structure with the transition from low temperature ferrimagnetic to room temperature ferromagnetic nature. These encouraged magnetic properties make this composition worthy to be further investigated on its magnetoelectric (ME) coupling effect mechanism or even its high frequencies (THz) ME coupling effect