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Lu W.,Tongji University | Xu Y.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | Shi J.,No. 1 Courtyard | Song Y.,Tongji University | Li X.,University of Shanghai for Science and Technology
Journal of Alloys and Compounds | Year: 2015

Giant magnetoimpedance (GMI) effect in amorphous soft magnetic materials has been intensively investigated owing to its promising technological applications. The GMI effect can be improved when an amorphous ferromagnetic material is subjected to proper heat treatments. In present work, in order to further improve the GMI effect in amorphous Co68Fe4Cr3Si15B10 ribbons, thermal annealing is employed to optimize the GMI effect of amorphous Co68Fe4Cr3Si15B10 ribbons. Magnetic measurements show that the soft magnetic properties of ribbons were affected significantly by thermal annealing. The saturation flux density of ribbons increases with increasing annealing temperature. Optimized annealing temperature of about 400 °C gives lowest coercivity, highest permeability and electric conductivity. The frequency dependence of GMI effect in annealed Co68Fe4Cr3Si15B10 ribbons is discussed in details. The maximum GMI value of about 220% and sensitivity of about 106%/Oe were achieved at the driven frequency of 3 MHz in the ribbon annealed at 400 °C. It is clear that the enhanced maximum GMI ratio and sensitivity for the sample annealed is caused by its increased saturated flux density, permeability, electrical conductivity and reduced coercivity. © 2015 Elsevier B.V. Source


Lu W.,Tongji University | Xu Y.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | Fang X.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | Song Y.,Tongji University | Li X.,University of Shanghai for Science and Technology
2015 IEEE International Magnetics Conference, INTERMAG 2015 | Year: 2015

Soft ferromagnetic amorphous ribbons are widely used for a wide range of applications, including high-frequency transformers and magnetic sensors. The recent discovery of a so-called giant mag-netoimpedance (GMI) effect in these alloys has made them very attractive candidates for making highly sensitive magnetic sensors [1]. GMI effects have been reported in Co-based amorphous ribbons owing to the high transverse permeability, due to the presence of a transversely oriented domain configuration [1]. Like Co-based amorphous wires, ribbons with CoFeSiB composition and nearly zero but negative magnetostriction, were found to show the largest GMI ratio among Co-based ribbons [2]. The GMI ratio reached a value as high as 160% at a frequency of 1 MHz in the (Co1-xFex)70Si12B18 (x = 0.057) amorphous ribbon with nearly zero magnetostriction. The research on GMI effect sensors is now focused on the material composition and structure of sensitive components [3]. In this presentation, we attempt to improve the GMI ratio of amorphous Co68Fe7Si15B10 alloy ribbons by introducing Ni element. © 2015 IEEE. Source


Lu W.,Tongji University | Xu Y.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | Fang X.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | Song Y.,Tongji University | Li X.,University of Shanghai for Science and Technology
2015 IEEE International Magnetics Conference, INTERMAG 2015 | Year: 2015

The FeRh alloy has been the subject of many experimental and theoretical studies over the last fifty years.[1-3] This interest is primarily due to the observation that the near-equiatomic phase of FeRh possesses a chemically ordered CsCl-type structure which exhibits an abrupt antiferromagnetic (AFM) to ferromagnetic (FM) transition with heating to a transition temperature of around 350K in the bulk and thin film forms. [1-3]. Previous researches show that the first order magnetostructural transition in ordered FeRh-based alloys is very sensitive to composition, temperature, external magnetic field and pressure [2-4]. This AFM-FM transition thus provides an interesting case to understand the nucleation and growth kinetics across a first order phase transition. Although many attempts have been made in order to clarify the underlying mechanism of this magnetostructural transition, the local origin responsible for the nucleation and growth of both FM and AFM phases and the coexistence of the two phases expected from a first-order transition is still under debate for this system. In addition, the nucleation and growth processes of both FM and AFM phases are crucial to the proposed applications. Previously, we have studied the magnetostructural phase transition behavior of polycrystalline FeRh thin films [5]. In this work, we report the temperature and time dependent magnetization of FM phase in epitaxial FeRh thin films across the AFM-FM transition on both heating and cooling process by vibrating sample magnetometer. © 2015 IEEE. Source


Song Y.,Tongji University | Lu W.,Tongji University | Xu Y.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | Shi J.,Anwaibeiyuan | Fang X.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology
Journal of Alloys and Compounds | Year: 2015

In this paper, single-crystalline Co7Fe3 nanowires were successfully electrodeposited into nanoporous anodic aluminum oxide (AAO) templates at different temperatures (20-60 °C). The morphology, crystallographic structure and magnetic properties of Co7Fe3 nanowires were studied. XRD and TEM results confirm that the Co7Fe3 nanowires have a <110> preferred orientation. With increasing bath temperature, the Co content is increased while Fe content is decreased in the Co7Fe3 nanowires. The compositional change in Co7Fe3 nanowires was investigated. Low bath temperature is beneficial to fabricate high-quality single-crystalline Co7Fe3 nanowires array and the growth mechanism of Co7Fe3 nanowires was also discussed. The hysteresis loop of the nanowires array demonstrates strong magnetic anisotropy with the easily magnetized direction being parallel to the nanowires axis. High coercivity (∼3440 Oe) and squareness (∼0.8) were obtained when the Co content is about 69 at.%. By controlling the growth conditions, we are able to prepare high-quality single-crystalline Co7Fe3 nanowires array with excellent magnetic properties. © 2015 Elsevier B.V. All rights reserved. Source


Lu W.,Tongji University | Jia M.,Tongji University | Ling M.,Tongji University | Xu Y.,National Key Laboratory of Science and Technology on Near surface Detection and Sensing Technology | And 4 more authors.
Journal of Alloys and Compounds | Year: 2015

In this paper, FeCo alloys with different phase structure and magnetic properties were successfully electrodeposited at different temperatures (20-90 °C). The crystallographic structure and magnetic properties of FeCo alloy films were studied. The Co content is increased while Fe content is decreased with increasing bath temperature. The X-ray diffraction and X-ray absorption near edge spectroscopy analysis reveal that the phase structures of the films strongly depend on the bath temperatures and a metastable α-Mn type phase (Co0.72Fe0.28) was formed at 50-80 °C. The saturation magnetization reaches a maximum value of 1890 emu/cc and coercivity reaches a minimum value of 10 Oe of the film electrodeposited at 50 °C in all the samples. © 2015 Elsevier B.V. All rights reserved. Source

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