Elsevier, 1999. 543 p.
The Handbook series Magnetic Materials is a continuation of the Handbook series Ferromagnetic Materials. When Peter Wohlfarth started the latter series, his original aim was to combine new developments in magnetism with the achievements of earlier compilations of monographs, producing a worthy successor to Bozorth's classical and monumental book Ferromagnetism. This is the main reason that Ferromagnetic Materials was initially chosen as title for the Handbook series, although the latter aimed at giving a more complete crosssection of magnetism than Bozorth's book.
In the last few decades magnetism has seen an enormous expansion into a variety of different areas of research, comprising the magnetism of several classes of novel materials that share with truly ferromagnetic materials only the presence of magnetic moments. For this reason the Editor and Publisher of this Handbook series have carefully reconsidered the title of the Handbook series and changed it into Magnetic Materials. It is with much pleasure that I can introduce to you now Volume 12 of this Handbook series.
The giant magnetoresistance or GMR is a prominent example of such expansion of magnetism. The giant magnetoresistance effect is found in heterostructures and was discovered only recently. The GMR of multilayers is induced by the variation of the angle between the magnetization of consecutive magnetic layers, and its discovery was preceded by the discovery of exchange coupling between magnetic layers across a non-magnetic metal layer. Under certain circumstances the coupling is antiferromagnetic and induces an antiparallel alignment of the magnetization of adjacent magnetic layers. When an exteal magnetic field aligns the magnetization of all magnetic layers in parallel, there is a giant decrease of the resistance of the multilayer. The discovery of interlayer exchange and GMR has lead to an enormous proliferation of experimental and theoretical studies on multilayers and more generally on magnetic nanostructures. GMR effects have been observed not only in exchange coupled magnetic multilayers but also in uncoupled multilayers, spin valve structures, multilayered nanowires and granular systems.
At present the giant magnetoresistance effect is used in various types of device such as sensors, read heads and magnetic RAM. Apart from the giant magnetoresistance effect and its applications, research on GMR has revealed a new class of magnetotransport phenomena which can be obtained in magnetic nanostructures by making use of the spin polarisation of carriers. This is a new field of research which is frequently referred to as spin electronics. Examples of emerging directions of research with important potential applications in this area are spin injection spin dependent tunnelling and magneto-Coulomb blockade. The review presented in Chapter 1 of this Volume is focused on GMR in magnetic multilayers. It includes an experimental overview of results obtained on conventional multilayers, spin valves, multilayers on grooved substrates and multilayered nanowires. The review comprises also theoretical models and employs the experimental data to discuss the current understanding of GMR and the underlying physics.
A key aspect of the study of the properties of thin magnetic films and multilayers is the relationship between the structural and magnetic properties of the material, which has become one of the most active areas of research in magnetism in recent years. Nuclear magnetic resonance (NMR) is a well-known technique that offers the possibility to obtain experimental information on atomic scale properties in systems with reduced dimensionality. A review of the results obtained by NMR on the latter systems is presented in Chapter 2 of this Volume. Because of its high sensitivity this method has the additional advantage that it provides not only experimental information on the nature of the magnetic and non-magnetic layers but also information on the nature of the interfaces. The Chapter is written in a tutorial style so that it can be helpful for many a scientist familiar with the preparation and properties of thin magnetic films but having little knowledge of the NMR of ferromagnetic materials.
Among the intermetallic rare-earth compounds with 3d transition metals, those that exhibit a magnetic instability of the 3d-subsystem are of particular interest. In combination with large magnetovolume effects, these compounds exhibit a number of characteristic properties that make them suitable for checking various physical theories. In the third Chapter of this Volume the attention is focused on such compounds, in which the d-electron subsystem is neither non-magnetic, nor carries a stable magnetic moment. Prominent examples of this group are the RCo2 Laves phase compounds in which the hybridised itinerant 3d-5d electron subsystem leads to exchange enhanced Pauli paramagnetism. Particular interest is paid to systems that undergo a metamagnetic transition, i.e. a field-induced magnetic phase transition from the paramagnetic to the ferromagnetic state under an exteal magnetic field exceeding a certain critical value. The chapter deals with basic concepts of the theory of itinerant-electron magnetism. It includes magnetic properties of the systems consisting of both itinerant electrons and localised spins, and discusses the effects of spin fluctuations on the magnetic behavior, heat capacity and magnetoresistance. Apart from metamagnetism, a comprehensible description is given of magnetovolume effects and spin fluctuations in the nearly ferromagnetic compounds. The itinerant-electron metamagnetism and the spin fluctuations are interesting not only in themselves. By studying these phenomena it is possible to understand more deeply some aspects of the theory of itinerant-electron metamagnetism and open up the possibilities incorporated in this theory for describing different unusual effects observed in experiments.
Magnetic refrigeration is a promising technology that can be used is quite a broad range of applications. It is based on the magnetocaloric effect associated with the entropy change occurring when a magnetic materials is isothermally subjected to a changing magnetic field and the temperature change when the field is changed adiabatically. Refrigeration can be achieved by using the magnetocaloric effect of ferromagnets in repeated magnetizationdemagnetization cycles under adiabatic and isothermal conditions. Research on magnetocaloric materials has received new impetus because of the need to realise room temperature magnetic refrigeration without the use of chlorofluorocarbons that are considered have a destructive impact on the ozone layer. The last decade has witnessed quite a strong development in magnetic cooling technology and research activities in this field have been extended to a variety of magnetocaloric materials, including amorphous alloys, nanocomposites, intermetallic compounds and perovskite type oxides. The many materials, their magnetocaloric efficiency as well as the physical principles behind it are reviewed in the last Chapter of this Volume.
Volume 12 of the Handbook on the Properties of Magnetic Materials, as the preceding volumes, has a dual purpose. As a textbook it is intended to be of assistance to those who wish to be introduced to a given topic in the field of magnetism without the need to read the vast amount of literature published. As a work of reference it is intended for scientists active in magnetism research. To this dual purpose, Volume 12 of the Handbook is composed of topical review articles written by leading authorities. In each of these articles an extensive description is given in graphical as well as in tabular form, much emphasis being placed on the discussion of the experimental material in the framework of physics, chemistry and material science.
The task to provide the readership with novel trends and achievements in magnetism would have been extremely difficult without the professionalism of the North Holland Physics Division of Elsevier Science B.V. , and I wish to thank Jonathan Clark and Wim Spaans for their great help and expertise.
Preface to Volume 12.
Contents.
Contents of Volumes 1-11.
List of Contributors.
Giant Magnetoresistance in Magnetic Multilayers.
NMR of Thin Magnetic Films and Superlattices.
Formation of 3d-Moments and Spin Fluctuations in Some Rare-Earth-Cobalt Compounds.
Magnetocaloric Effect in the Vicinity of Phase Transitions.
Author Index.
Subject Index.
Materials Index.
The Handbook series Magnetic Materials is a continuation of the Handbook series Ferromagnetic Materials. When Peter Wohlfarth started the latter series, his original aim was to combine new developments in magnetism with the achievements of earlier compilations of monographs, producing a worthy successor to Bozorth's classical and monumental book Ferromagnetism. This is the main reason that Ferromagnetic Materials was initially chosen as title for the Handbook series, although the latter aimed at giving a more complete crosssection of magnetism than Bozorth's book.
In the last few decades magnetism has seen an enormous expansion into a variety of different areas of research, comprising the magnetism of several classes of novel materials that share with truly ferromagnetic materials only the presence of magnetic moments. For this reason the Editor and Publisher of this Handbook series have carefully reconsidered the title of the Handbook series and changed it into Magnetic Materials. It is with much pleasure that I can introduce to you now Volume 12 of this Handbook series.
The giant magnetoresistance or GMR is a prominent example of such expansion of magnetism. The giant magnetoresistance effect is found in heterostructures and was discovered only recently. The GMR of multilayers is induced by the variation of the angle between the magnetization of consecutive magnetic layers, and its discovery was preceded by the discovery of exchange coupling between magnetic layers across a non-magnetic metal layer. Under certain circumstances the coupling is antiferromagnetic and induces an antiparallel alignment of the magnetization of adjacent magnetic layers. When an exteal magnetic field aligns the magnetization of all magnetic layers in parallel, there is a giant decrease of the resistance of the multilayer. The discovery of interlayer exchange and GMR has lead to an enormous proliferation of experimental and theoretical studies on multilayers and more generally on magnetic nanostructures. GMR effects have been observed not only in exchange coupled magnetic multilayers but also in uncoupled multilayers, spin valve structures, multilayered nanowires and granular systems.
At present the giant magnetoresistance effect is used in various types of device such as sensors, read heads and magnetic RAM. Apart from the giant magnetoresistance effect and its applications, research on GMR has revealed a new class of magnetotransport phenomena which can be obtained in magnetic nanostructures by making use of the spin polarisation of carriers. This is a new field of research which is frequently referred to as spin electronics. Examples of emerging directions of research with important potential applications in this area are spin injection spin dependent tunnelling and magneto-Coulomb blockade. The review presented in Chapter 1 of this Volume is focused on GMR in magnetic multilayers. It includes an experimental overview of results obtained on conventional multilayers, spin valves, multilayers on grooved substrates and multilayered nanowires. The review comprises also theoretical models and employs the experimental data to discuss the current understanding of GMR and the underlying physics.
A key aspect of the study of the properties of thin magnetic films and multilayers is the relationship between the structural and magnetic properties of the material, which has become one of the most active areas of research in magnetism in recent years. Nuclear magnetic resonance (NMR) is a well-known technique that offers the possibility to obtain experimental information on atomic scale properties in systems with reduced dimensionality. A review of the results obtained by NMR on the latter systems is presented in Chapter 2 of this Volume. Because of its high sensitivity this method has the additional advantage that it provides not only experimental information on the nature of the magnetic and non-magnetic layers but also information on the nature of the interfaces. The Chapter is written in a tutorial style so that it can be helpful for many a scientist familiar with the preparation and properties of thin magnetic films but having little knowledge of the NMR of ferromagnetic materials.
Among the intermetallic rare-earth compounds with 3d transition metals, those that exhibit a magnetic instability of the 3d-subsystem are of particular interest. In combination with large magnetovolume effects, these compounds exhibit a number of characteristic properties that make them suitable for checking various physical theories. In the third Chapter of this Volume the attention is focused on such compounds, in which the d-electron subsystem is neither non-magnetic, nor carries a stable magnetic moment. Prominent examples of this group are the RCo2 Laves phase compounds in which the hybridised itinerant 3d-5d electron subsystem leads to exchange enhanced Pauli paramagnetism. Particular interest is paid to systems that undergo a metamagnetic transition, i.e. a field-induced magnetic phase transition from the paramagnetic to the ferromagnetic state under an exteal magnetic field exceeding a certain critical value. The chapter deals with basic concepts of the theory of itinerant-electron magnetism. It includes magnetic properties of the systems consisting of both itinerant electrons and localised spins, and discusses the effects of spin fluctuations on the magnetic behavior, heat capacity and magnetoresistance. Apart from metamagnetism, a comprehensible description is given of magnetovolume effects and spin fluctuations in the nearly ferromagnetic compounds. The itinerant-electron metamagnetism and the spin fluctuations are interesting not only in themselves. By studying these phenomena it is possible to understand more deeply some aspects of the theory of itinerant-electron metamagnetism and open up the possibilities incorporated in this theory for describing different unusual effects observed in experiments.
Magnetic refrigeration is a promising technology that can be used is quite a broad range of applications. It is based on the magnetocaloric effect associated with the entropy change occurring when a magnetic materials is isothermally subjected to a changing magnetic field and the temperature change when the field is changed adiabatically. Refrigeration can be achieved by using the magnetocaloric effect of ferromagnets in repeated magnetizationdemagnetization cycles under adiabatic and isothermal conditions. Research on magnetocaloric materials has received new impetus because of the need to realise room temperature magnetic refrigeration without the use of chlorofluorocarbons that are considered have a destructive impact on the ozone layer. The last decade has witnessed quite a strong development in magnetic cooling technology and research activities in this field have been extended to a variety of magnetocaloric materials, including amorphous alloys, nanocomposites, intermetallic compounds and perovskite type oxides. The many materials, their magnetocaloric efficiency as well as the physical principles behind it are reviewed in the last Chapter of this Volume.
Volume 12 of the Handbook on the Properties of Magnetic Materials, as the preceding volumes, has a dual purpose. As a textbook it is intended to be of assistance to those who wish to be introduced to a given topic in the field of magnetism without the need to read the vast amount of literature published. As a work of reference it is intended for scientists active in magnetism research. To this dual purpose, Volume 12 of the Handbook is composed of topical review articles written by leading authorities. In each of these articles an extensive description is given in graphical as well as in tabular form, much emphasis being placed on the discussion of the experimental material in the framework of physics, chemistry and material science.
The task to provide the readership with novel trends and achievements in magnetism would have been extremely difficult without the professionalism of the North Holland Physics Division of Elsevier Science B.V. , and I wish to thank Jonathan Clark and Wim Spaans for their great help and expertise.
Preface to Volume 12.
Contents.
Contents of Volumes 1-11.
List of Contributors.
Giant Magnetoresistance in Magnetic Multilayers.
NMR of Thin Magnetic Films and Superlattices.
Formation of 3d-Moments and Spin Fluctuations in Some Rare-Earth-Cobalt Compounds.
Magnetocaloric Effect in the Vicinity of Phase Transitions.
Author Index.
Subject Index.
Materials Index.