Recent Patents on Materials Science - Volume 7, Issue 2, 2014

From time immemorial, magnetism and magnetic materials (the materials which can respond to an applied magnetic field) have been a fascination for mankind. Later, scientists and engineers successfully employed this ever attracting property into numerous machines and devices, while most of those devices were based on electromagnetic induction. On the other hand, a classical analogue to the magnetic properties, ferroelectricity [1-3], the generation of spontaneous polarisation in the presence of an applied electric field, began to be a hot topic of research on at a later stage. Other closely related properties like piezoelectricity [4-6] (conversion of mechanical stress in to electric signals), pyroelectricity [7] (conversion of temperature difference into voltage) etc. were also investigated widely. As magnetism and electricity have always been treated on similar lines, scientists started dreaming about a material possessing these two properties together in the same phase bearing in mind the potential of such materials in microelectronics and micromechanics. However, these two properties are hard to be observed in the same phase at normal temperatures as they are governed by mutually exclusive physical laws [8, 9]. The most exciting and prevalent property of multiferroics and magnetoelectrics is controlling and manipulating the ferromagnetism with electric fields which paved way to the areas of information storage, actuation and sensing [10-19]. Rapid advancement of the property of electric field control of the spin of carriers has broadened the applications of multiferroics and magnetoelectrics to the field of spintronics [20]. Spin filter junction is one of the special manifestations of the device architecture in the above aspect using multiferroic tunnel junction [21-27]. As a part of this discovery, multiferroic thin films deserve an important role because critical thickness is a strongly dependent parameter for determining the properties of an electrode [28-30]. A strong focus on spin wave devices leads to the invention of spin wave amplifiers [31] and magnetoelectric generators, where the ferroelectric oscillations are controlled by magnetic field and vice versa. Recent discoveries reveal that the potential applications of multiferroics are beyond the electrical control of magnetic ordering which includes the invention of electrically controllable logic elements or nanoscale storage devices. Multiferroic Magnetoelectric composite nanostructures have been developed as a prerequisite for micro fabrication techniques due to their interesting interface design and atomic arrangements [32, 33]. It could be used as magnetoelectric read heads where the output waveforms followed the wave function of AC magnetic excitation signals [34]. Artificially engineered multiferroics can be made possible by properly designing magnetoelectric heterostructures which are the composites of piezo/ferro electric structures and a career mediated magnet. A diluted magnetic semiconductor or a double exchange ferromagnet can serve the purpose. The magneto electric coupling in this case is effected through the interface electric field [28, 35, 36]. 1-D Heterostructures or multiwalled structures are advantageous because of their large interfacial surface area compared to the conventional heterostructures [28, 37] and hence allow strong magneto electric coupling. Additionally, this geometry can reduce lattice deformation induced suppression of the magnetic as well as piezoelectric response. The concept of multiferroic behavior can be extended to other physical phenomena, such as electron transport, which can expand the application potential [38]. This edition of Recent Patents on Materials Science is dedicated to magnetoelectrics and multiferroics. Recent patents and highly relevant publications are analysed in depth so as to give the readers better insight into the later developments in the device level applications of these materials. The issue covers wide range of applications of single phase as well as composite type multiferroics. Chapter 1 is a lead article prepared by reviewing the recent patents and most relevant publications in the field of multiferroics and magneto electrics. Chapter 2 gives a detailed investigation on spintronic applications of multiferroics and magnetoelectrics. Different synthesis mechanisms for thin film multiferroics is dealt in the following two chapters. In one of these chapters, thrust is given on the synthesis of thick and thin film multiferroics by electrophoretic deposition, while the other chapter describes the synthesis of multiferroic and magnetoelectric composite thin films. There exists enough scope for further improving the properties of these materials and unravelling novel applications, fabrication of novel devices and explaining the deep underlying physical laws governing the properties. Hence I wish this special issue can guide researchers working in this area, especially those focusing on device level research towards unseen applications.

Multiferroics and magnetoelectrics are closely correlated research areas which assume high level of research significance owing to their versatile application potential in devices like memory/storage devices, sensors/transducers, FETs, transistors etc. Extensive research has already been carried out in this particular area and numerous review articles have been published detailing their theoretical concepts, simulation of their properties, development of novel materials for device applications, lead free alternatives etc. However, most of the reviews on this topic are limited to research articles. A systematic review of recent patents in different aspects of multiferroics and magnetoelectrics will thus be a promising article which can outline the device level application of these materials in a comprehensive way. In this review article, general developments in the fabrication of novel devices based on multiferroic and magneto electric materials are discussed. Basic understanding of the existing theories in the field is also explained for non-expert readers. Pioneering research achievements published in research articles are also cited along with the vast coverage of patents.

Composites (3-0 and 2-0) and multilayers (2-2 geometry) of magnetoelectric multiferroics have recently attracted immense research interest owing to their potential applications like memory/storage devices, FETs, energy harvesters, sensors and transducers. Thin film based multiferroics and magnetoelectrics have special significance because of their direct integration into the device fabrication industry. Hence, a fundamental research in this area along with the fabrication of versatile devices needs a thorough investigation. This review article mainly focuses on the developments of device level works in this particular area in which the discussion of recent patents is highlighted. Generally, thin film magneto electrics and multiferroics show weak magneto electric coupling properties compared to their bulk cousins due to their high substrate clamping. However, some of the recent research developments in thin film based magneto electrics and multiferroics show promising future. In this article, a general patent search in thin films is provided along with a special thrust given to the nanocomposite based multiferroics and magneto electric films.

Spintronics is a novel and emerging area of research in which both the intrinsic spin of the electron and its associated magnetic moment are exploited in addition to its charge. Spintronic based devices are being developed enormously and the researches in this area are attaining tremendous pace recently. In this particular article, details of multiferroic properties, magneto electric coupling etc. are discussed. A general introduction to spintronics and associated physics is discussed. Development and progress in spintronics based devices are elaborated. Final sessions are dedicated for the description of recent patents on spintronics devices in which multiferroic material is a constituent.

With the evolution of microelectronics, the size of devices is getting smaller and smaller with hybrid functionalities. The thick film technology is becoming more important for miniaturization in the field of electronics to fabricate surface mounted devices, hybrid integrated circuits and sensors. A number of established techniques for thick film fabrication such as screen printing, ink-jetting, tape casting and electrophoretic deposition (EPD) have been reported. Among all the above techniques, electrophoretic technique has gained considerable importance for a variety of applications in view of its high reliability, low cost, high performance and flexibility to produce films with variable thicknesses ranging from hundreds of nanometres to few micro meters. In the last few decades, EPD has been employed as a major fabrication technique for thin/thick films of ferrite, ferroelectric and multiferroic materials for their applications in high frequency, data storage and hybrid functional devices respectively. The review starts with the introduction on multiferroic and magnetoelectrics followed by the fundamental and possible mechanisms as well as some significant results on multiferroic properties of materials. In the application section, patents related to the fabrication and devices have been discussed. In the later part of the review, various aspects of the electrophoretic deposition were discussed for the fabrication of thick composite films. The implementation of EPD for the fabrication of multiferroic and magnetoelectric films was briefed based on literature.

The state-of-the-art Nafion® membrane suffers from several shortcomings such as high cost, water dependent conductivity and loss of efficiency at elevated temperature. In contrast particulate filled Nafion® and other nanocomposite polymer electrolyte membranes (PEMs) offer combination of several attractive properties such as high water retention capacity, dimensional, thermal and mechanical stability, excellent conductivity, durability and resistance to fuel cross-over. In this study several research papers and patents related to chemical modification of fillers, different fabrication methods and functional properties of several particulate filled nanocomposite membranes are discussed concisely. The mechanism and role of different particulate fillers in achieving the superior performance of membrane have been demonstrated scientifically. Solution casting, sol-gel, in situ impregnation and self-assembly are common approaches employed for synthesis of nanocomposite PEMs. The functional properties of silica, titania, zirconia, clay, and zeolite hygroscopic fillers filled PEMs in particular are reviewed in details with respect to fuel cell membrane applications.

The present review describes the most recent patents and outlines the progress made over the last decade in the field of wastewater treatment focusing on the application of Coagulation/Flocculation (C/F) process, which is mainly used as primary treatment for the effective removal of colloidal particles and organic matter. Various materials/chemical reagents have been developed in recent years as coagulation/flocculation agents. Among them are inorganic-based coagulants, organic-based flocculants, as well as hybrid materials, or tannin-based polymeric coagulants. Furthermore, a recent patent application for treating wastewater is using nanoparticles of clay as anionic coagulant agent. In many sensitive catchment areas, the effective removal of phosphorus is also required. Several alternative processes, methods and treatment systems have been provided in recent patents for lowering the concentration of phosphorus in wastewaters, noting that the conventional use of alum or ferric chloride for phosphorous removal is rather problematic due to acidity of coagulants, being added to the wastewater. A coagulation-sedimentation apparatus is specifically designed to treat water at higher rates and a more recent patent discloses a system for continuous optimization of the relevant wastewater treatment.

The hardness and electrical resistivity of CuW alloy before and after high pressure heat treatment were tested, its microstructure was also analyzed by metallurgical microscope, scanning electron microscope and transmission electron microscopy, and the effect of high pressure treatment on hardness and electrical resistivity properties of CuW alloy was discussed. It showed that high pressure could increase hardness and room-temperature electrical resistivity of CuW alloy, which was 155HB and 3.5974x10-6 Ω.cm after 1 GPa pressure heat treatment at 900°C lasting for 20 minutes respectively, increasing by 27.05% and 6.30% as against the infiltrated CuW alloy. But the variation of the hardness and roomtemperature electrical resistivity is not obvious with increasing pressure in the range of 1-6GPa. It is mainly because the high pressure heat treatment can increase the compactness and internal dislocation density of CuW alloy. The paper is based on the following patents: US20140093420 (2014), US20130142687 (2013), CN2012102773462 (2012), CN2012102127627 (2012), CN2008101307419 (2008), CN2012102168235 (2012), CN2010101914739 (2010), CN2012102660717 (2012).