Alexander Chizhik Julian Gonzalez

Transcription

1 Alexander Chizhik Julian Gonzalez

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3 Magnetic Microwires

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5 Alexander Chizhik Julian Gonzalez Magnetic Microwires A Magneto- Optical Study

6 Published by Pan Stanford Publishing Pte. Ltd. Penthouse Level, Suntec Tower 3 8 Temasek Boulevard Singapore editorial@panstanford.com Web: British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Magnetic Microwires: A Magneto-Optical Study Copyright 2014 Pan Stanford Publishing Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN (Hardcover) ISBN (ebook) Printed in the USA

7 Contents Preface ix 1. Kerr Effect as Method of Investigation of Magnetization Reversal in Magnetic Wires Introduction MOKE Magnetometer (Loop Tracer) MOKE Polarizing Microscopy MOKE-Modified Sixtus Tonks Method 5 2. Cold-Drawn Fe-Rich Amorphous Wire Introduction Two Magnetic Phases in Cold-Drawn Fe-Rich Amorphous Wire Helical Magnetic Structure Conventional Co-Rich Amorphous Wire Introduction Magnetization Reversal in Circular and Axial Magnetic Fields Model of Surface Magnetization Reversal Effect of a Thermal Treatment As-Quenched Wire Annealed Wire Torsion-Annealed Wire Correlation between Switching Field and Wire Length Vortex-Type Domain Structure 45

8 vi Contents 4. Interaction between Glass-Covered Microwires Introduction Fe-Rich Microwires Co-Rich Microwires Circular Magnetic Bistability in Co-Rich Amorphous Microwires Introduction Circular Magnetic Bistability Effect Related with a Large Circular Barkhausen Jump Circular Magnetic Bistability Induced by Tensile Stress Domain Structure in Glass-Covered Co-Rich Microwires in Presence of Tensile Stress Effect of High-Frequency Driving Current on Magnetization Reversal in Co-Rich Amorphous Microwires Introduction Experimental Details Surface Magnetization Reversal in Axial Magnetic Field Surface Magnetization Reversal in Circular Magnetic Field Relation between Surface Magnetization Reversal and Magnetoimpedance Introduction Optimization of Giant Magnetoimpedance in Co-Rich Amorphous Microwires Circular Surface Magnetization Reversal and Magnetoimpedance Axial Surface Magnetization Reversal and Magnetoimpedance Correlation of Surface Domain Structure and Magnetoimpedance Helical Magnetic Structure Introduction 119

9 Contents vii 8.2 Magneto-Optical Determination of Helical Magnetic Structure Transverse Kerr Effect Dependencies Helical Magnetic Structure in Microwires with Different Value of Geometric Ratio Surface and Bulk Magnetic Hysteresis Loops of Co-Rich Glass Covered Microwires Experimental Determination of Limit Angle of Helical Anisotropy in Amorphous Magnetic Microwires Correlation of Magnetic Behavior with Diameter of Microwire Magnetic Domain Structure Studied by Bitter Technique Magnetization Reversal in Crossed Magnetic Field Visualization of Barkhausen Jump Introduction Experiment Calculation Magnetization Reversal in Glass-Covered Nano-Wires of Cylindrical Shape Magnetic Domain Wall Dynamics in Co-Rich Glass-Covered Microwires Introduction Experiment Comparison of Induction and MOKE Methods Domain Walls Dynamics in Co-Rich Microwires Nucleation and Transformation of Circular Magnetic Domain Structure: Control of Domain Nucleation Introduction Circular Field Induced Nucleation and Transformation of Circular Magnetic Domains Control of Domain Nucleation 194

10 viii Contents 14. Magnetization Reversal in Co-Rich Microwires with Different Values of Magnetostriction Introduction Experimental Results and Discussions Application of Magneto-Optical Indicator Film Method to Study Domain Magnetic Structure in Microwires Introduction Experiment Experimental Results and Discussion 209 Index 215

11 Preface The idea of studying magnetic wires using the magneto-optic technique appeared in the late nineties of the 20th century as a response to the discovery of the giant magneto-impedance (GMI) effect one of the most promising effects observed in magnetic wires. This idea looked very attractive because of the following reasons. The systematic magneto-optical investigation of the noplane objects had not been performed ever before. Usually the magneto-optical technique is used to study plane objects, and the present task of the magneto-optical investigation of cylindrically shaped samples attracted me by unusual and original experimental configuration. By that time I had acquired a good enough background as an experimentalist in magneto-optics, obtained in the well-known magneto-optical school belonging to the B. Verkin Institute for Low Temperature Physics and Engineering in Kharkov, Ukraine, and with 20 years of joint work with such great scientists as academicians V. V. Eremenko, N. F. Kharchenko, and S. L. Gnatchenko, who have taught me to always search the original promising scientific tasks. Another motivation was determined by the surface nature of the GMI effect the penetration depth of the ac current changes in the presence of dc applied magnetic field. As it is known, the magneto-optical Kerr effect, which is usually used for the investigation of non-transparent objects, is also the surface effect the light reflected from the sample contains the information about the magnetic behaviour in the thin near surface layer. In this way, the task of obtaining a deep understanding of the surface magnetization processes that affect the skin effect in magnetic conductors has found a suitable powerful method. It is necessary to remark that the great variety of the chemical composition, sizes, and geometric ratios (metallic nucleus)/(glass shell) promises a wide range of interesting magnetic effects to be studied.

12 Preface The magneto-optical study of magnetic wires was initiated by Profs. J. M. Blanco and J. Gonzalez, whom I appreciate very much for their kind and farsighted invitation of collaboration. The main part of the magneto-optical investigations was performed in the Laboratory of Magnetism of the University of Basque Country, Spain, with which I was associated during the past 10 years of fruitful activity. It is necessary to note the creative and open atmosphere in the lab formed by Prof. A. Zhukov, Dr. V. Zhukova and Dr. M. Ipatov. Also, a significant number of the magneto-optical images presented in the book were obtained in the Laboratory of Magnetism of the University of Bialystok, Poland, under the direction of Prof. A. Maziewski. These images are the result of my collaboration with Prof. A. Stupakiewicz, a great specialist in magneto-optics. An essential objective of our study was to perform a theoretical analysis to establish the depth of the understanding of the discovered effects. I have performed this analysis in association with Prof. K. Kulakowski, Dr. P. Gawronski from Krakow, Poland, and Prof. V. Zablotskii from Prague, Czech Republic. Almost all the glass-covered microwires studied in our laboratory have been supplied by a small but very powerful company, Tamag Iberica. The company has a wide international collaboration from Moldova to Japan and has always provided us the best experimental material. Two directions were prioritized in our investigations. First, I sought the discovery of new effects, and I succeeded in it: circular bistability, visualization of the giant Barkhausen jump, correlation between the GMI effect and surface magnetization, etc. The discovery of these phenomena has led us to new level of the understanding of the physical processes that take place in magnetic wires. The significant experimental success was conditioned by the realization of the original experimental configuration named magneto-optical Kerr effect without external magnetic field : The studies have been performed only in the presence of a circular magnetic field produced by the electric current flowing along the microwire. The other fundamental task was the optimization of the magnetic, electrical and mechanical properties of the wires taking into account the technological application. The performance of the systematic study of a wide series of wires of different compositions

13 Preface xi and geometric ratios permitted us to determine the methodical features that help to predicate and control the key parameters of microwires. The contents of this book reflect this duality of our investigation. The book describes the basic physical effects and the chapters are devoted to the detailed elucidation of the observed features. Directing the attention to the glass-covered wires of the micrometer scale, I have advanced to the nano-area. Now it is clear that the cylindrical symmetry and the specific stress distribution induced by the glass covering are the key parameters that provide the competitive technological application of microwires. The idea is to move to the nanoscale while maintaining the achieved optimal parameters of microwires. The first steps of this shift to the nano range are presented in this book as an example of the versatility of the basic effects initially discovered for the microscale. I hope this book will serve as a landmark that encourages us to apply the experimental and theoretical efforts to the discovery of new surprising effects in magnetic wires. I would like to express special thanks to my wife, Marina, daughter, Daria, and mother, Zoia, for their continuous support and their interest in my work. Alexander Chizhik

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