Colossal Magnetoresistive Manganites

The physics of transition metal oxides has become a central topic of interest to condensed-matter scientists ever since high temperature superconductivity was discovered in hole-doped cuprates with perovskite-like structures. Although the renewed interest in hole-doped perovskite manganites following the discovery of their colossal magnetoresistance (CMR) properties, began in 1993 about a decade after the discovery of high temperature superconductivity, their first investigation started as early as 1950 and basic theoretical ideas were developed during 1951-1960. Experience in sample preparation and characterization, and in growth of single crystals and epitaxial thin films, gained during the research on high temperature superconductors, and the development of theoretical tools, were very efficiently used in research on CMR manganites. In early nineties it appeared to many condensed matter physicists that although the problem of high temperature superconductivity is a difficult one to solve, a quantitative understanding of CMR phenomena might be well within reach. This book is intended to be an account of the latest developments in the phys ics of CMR manganites. When I planned this book back in 2000, I thought that research on the physics of CMR manganites would be more or less consolidated by the time this would be published. I was obviously very optimistic indeed. We are now in 2003 and we still do not have a quantitative understanding of the central CMR effect. Meanwhile the field has expanded. It is still a very active field of research on both the experimental and theoretical fronts.

The features and mechanism of Colossal Magnetoresistance, or CMR, in manganese oxides as well as device physics are highlighted in this book, with a focus on tunneling MR for some artificial structures. Underlying new science, such as tunable electron-lattice interaction in a metal and roles of orbital degrees of freedom in producing an unconventional metallic feature, is also discussed. The book provides a systematic exploration of the CMR materials and an extensive investigation of the electronic phenomena of those compounds by various experimental means.

Metal oxides constitute one of the most amazing classes of materials with a wide range of properties. They exhibit a variety of phenomena, such as ferroelectricity, ferromagnetism and superconductivity. A new aspect of metal oxides -- colossal magnetoresistance exhibited by certain manganese oxides, in particular rare earth manganates of perovskite structure -- has received much attention in the last four years. Some of these oxides show 100% magnetoresistance and have much potential for technological applications. Previously this phenomenon was found only in layered and granular metallic materials. Studies of colossal magnetoresistance have led to the discovery of many other new phenomena and properties such as charge ordering and orbital ordering. In view of the importance of colossal magnetoresistance, charge ordering and related phenomena exhibited by oxides to the physics and chemistry of solid materials, it is necessary and timely to have a book dealing with these topics. This book begins with a review of the subject followed by contributions from a number of experts which cover the present status of the subject.

The features and mechanism of Colossal Magnetoresistance, or CMR, in manganese oxides as well as device physics are highlighted in this book, with a focus on tunneling MR for some artificial structures. Underlying new science, such as tunable electron-lattice interaction in a metal and roles of orbital degrees of freedom in producing an unconventio

This series of books, which is published at the rate of about one per year, addresses fundamental problems in materials science. The contents cover a broad range of topics from small clusters of atoms to engineering materials and involves chemistry, physics, materials science and engineering, with length scales ranging from Ångstroms up to millimeters. The emphasis is on basic science rather than on applications. Each book focuses on a single area of current interest and brings together leading experts to give an up to date discussion of their work and the work of others. Each article contains enough references that the interested reader can access the relevant literature. Thanks are given to the Center for Fundamental Materials Research at Michigan State University for supporting this series. M. F. Thorpe, Series Editor E mail: thorpe@pa. msu. edu V PREFACE This book records invited lectures given at the workshop on Physics of Manganites, held at Michigan State University, July 26 29, 1998. Doped manganites are an interesting class of compounds that show both metal insulator and ferromagnetic to paramagnetic transitions at the same temperature. This was discovered in the early 1950s by Jonker and van Santen and basic theoretical ideas were developed by Zener (1951), Anderson and Hasegawa (1955), and deGennes (1960) to explain these transitions and related interesting observations.

The study of the spontaneous formation of nanostructures in single crystals of several compounds is now a major area of research in strongly correlated electrons. These structures appear to originate in the competition of phases. The book addresses nanoscale phase separation, focusing on the manganese oxides known as manganites that have the colossal magnetoresistance (CMR) effect of potential relevance for device applications. It is argued that the nanostructures are at the heart of the CMR phenomenon. The book contains updated information on manganite research directed to experts, both theorists and experimentalists. However, graduate students or postdocs will find considerable introductory material, including elements of computational physics.

Neutron Scattering from Magnetic Materials is a comprehensive account of the present state of the art in the use of the neutron scattering for the study of magnetic materials. The chapters have been written by well-known researchers who are at the forefront of this field and have contributed directly to the development of the techniques described. Neutron scattering probes magnetic phenomena directly. The generalized magnetic susceptibility, which can be expressed as a function of wave vector and energy, contains all the information there is to know about the statics and dynamics of a magnetic system and this quantity is directly related to the neutron scattering cross section. Polarized neutron scattering techniques raise the sophistication of measurements to even greater levels and gives additional information in many cases. The present book is largely devoted to the application of polarized neutron scattering to the study of magnetic materials. It will be of particular interest to graduate students and researchers who plan to investigate magnetic materials using neutron scattering. · Written by a group of scientist who have contributed directly in developing the techniques described. · A complete treatment of the polarized neutron scattering not available in literature. · Gives practical hits to solve magnetic structure and determine exchange interactions in magnetic solids. · Application of neutron scattering to the study of the novel electronic materials.

The fact that magnetite (Fe304) was already known in the Greek era as a peculiar mineral is indicative of the long history of transition metal oxides as useful materials. The discovery of high-temperature superconductivity in 1986 has renewed interest in transition metal oxides. High-temperature su perconductors are all cuprates. Why is it? To answer to this question, we must understand the electronic states in the cuprates. Transition metal oxides are also familiar as magnets. They might be found stuck on the door of your kitchen refrigerator. Magnetic materials are valuable not only as magnets but as electronics materials. Manganites have received special attention recently because of their extremely large magnetoresistance, an effect so large that it is called colossal magnetoresistance (CMR). What is the difference between high-temperature superconducting cuprates and CMR manganites? Elements with incomplete d shells in the periodic table are called tran sition elements. Among them, the following eight elements with the atomic numbers from 22 to 29, i. e. , Ti, V, Cr, Mn, Fe, Co, Ni and Cu are the most im portant. These elements make compounds with oxygen and present a variety of properties. High-temperature superconductivity and CMR are examples. Most of the textbooks on magnetism discuss the magnetic properties of transition metal oxides. However, when one studies magnetism using tradi tional textbooks, one finds that the transport properties are not introduced in the initial stages.