Elsevier, 2002. 429 p. ISBN: 0 444 51144 X
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 cross-section 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 14 of this Handbook series.
Magnetoelectronics is a novel and rapidly developing field, where new functionalities are created by combining and utilizing simultaneously two degrees of freedom, the charge and the spin of the carriers. This new field is frequently referred to as spinelectronics or spintronics. It includes spin-utilizing devices that need neither a magnetic field nor magnetic materials. In semiconductor devices, the spin of the carriers has only played a very modest role so far because well established semiconductor devices are non-magnetic and show only negligible effects of spin. However, interesting enhanced spin-related phenomena were observed in magnetic semiconductors and diluted magnetic semiconductors already many years ago. A review of diluted magnetic semiconductors has been presented by Kossut and Dobrowolski in Volume
7. In a way compatible with the present-day electronic materials, diluted magnetic semiconductors can be prepared by introducing high concentrations of magnetic ions into the parent non-magnetic semiconductors. Semiconductors based on III-V compound are widely used for highspeed electronic devices as well as for optoelectronic devices. Moreover, heterostructures based on the GaAs/(Al,Ga)As systems have proven to be a convenient testing ground for novel physical concepts and devices. The introduction of magnetism into 111-Vcompounds therefore, opens up the possibility of using a variety of magnetic and/or spin-dependent phenomena. not present in the conventional non-magnetic parent compounds. Preparation and properties of ferromagnetic III-V based semiconductors are reviewed in Chapter 1, including heterostructures.
Nanoscale thin films and multilayers, nanocrystalline magnetic materials, granular films, and amorphous alloys have attracted much attention in the last few decades, in the field of basic research as well as in the broader field of materials science. Such heterogeneous materials display uncommon magnetic properties that virtually do not occur in bulk materials. This is true, in particular with respect to surface (interface) magnetic anisotropy and surface (interface) magnetostrictive strains and giant magnetoresistance. The local atomic arrangement at the interface differs strongly from that in the bulk. The local symmetry is lowered, so that some interactions are changed or are missing altogether. The interface atoms may be envisaged as forming a new phase and some properties characteristic of this phase may become predominant for the entire system. This becomes particularly evident in the case of interfacial magnetostriction which can lead to a decrease (almost to zero) or to an increase (over the bulk value) of the resulting magnetostriction of the nanoscale system. In Chapter 2 of the present Volume, the magnetoelasticity of heterogeneous materials is treated in much details. Generally, the dimensions of a magnetostrictive material change when the material is subjected to a change in magnetic field. Hence, magnetostrictive materials can be applied in transducers, which directly convert electrical energy into mechanical energy. They are useful in the manufacture of sensors, actuators, controllers, force and displacement as well as other electro-acoustic devices. For these applications, transducer materials in the form of thin films are of special interest because cost-effective mass production is possible, compatible to microsystem processing technologies. In addition, magnetostrictive thin films are particularly promising as microactuator elements like cantilevers or membranes, since they combine high-energy output, high-frequency and remote-control operation. Due to this potential, interest in such giant magnetostrictive thin films has rapidly grown over the past few years and results are reviewed in this Chapter
2. This chapter is a logical
extension of previous wok on magneto-elastic effects published in this handbook series over the years. Bulk giant magnetostrictive materials based on rare-earth compounds were reviewed by Clark (Volume I), quadrupolar interactions and magneto-elastic effects in rare-earth intermetallics were treated by Morin and Schmitt (Volume 5) and thermal expansion anomalies and spontaneous magnetostriction of these compounds were reviewed by Andreev (Volume 8).
There are various forms of the interplay of magnetism and superconductivity, which can be divided into competition and coexistence phenomena. For instance, a strong competition is found in high-Te cuprates. In these materials, depending on the doping rate, either Neel-type antiferromagnetism or superconductivity may occur, both based on the copper d-electrons. A coexistence of localized magnetic moments (e.g. from 4f-elements) with superconductivity is known to occur in systems where the concentration of these moments is sufficiently small or where they are antiferromagnetically ordered and only weakly coupled to the conduction electrons. A review on the interplay of magnetism and superconductivity in various types of intermetallic compounds has been presented by Fischer in Volume 5 of the Handbook. An extensive review on the normal state
magnetic properties of cuprate high-temperature superconductors and related materials has been presented by Johnston in Volume
10. A striking feature distinguishing the superconducting RT2B2C compounds from other superconductors is the following: For certain combinations of the R and T elements superconductivity and antiferromagnetic order have been found to coexist and more importantly, the values of the magnetic ordering temperature TN are comparable in magnitude with the values of the superconducting transition temperatures Te . This means that the magnetic energy is comparable with the superconducting condensation energy. Therefore the investigation of these compounds is expected to result in new insights into the interplay between superconductivity and magnetism. The high values of T ~ demand that in the quateary borocarbides, different
from the situation in high-Tc cuprates and the classical magnetic superconductors, the exchange coupling between the rare-earth magnetic moments is the dominant magnetic interaction rather than magnetostatic interaction. Obviously the exchange coupling is mediated by the conduction electrons, Consequently also the interaction between the magnetic moments and the conduction electrons must be relatively strong in the quateary borocarbides. A comprehensive review on the current status of research of the quateary borocarbide superconductors, starting from their discovery, is presented in Chapter 3 of this Volume. For the reasons mentioned, the magnetic and as well as the superconducting properties of this interesting class of materials is discussed together.
During the years, intermetallic gadolinium compounds have adopted a special position in the study of 4f electron magnetism. The reason for this is the fact that the gadolinium moment consists only of a pure spin moment, orbital contributions to the moment being absent. As a consequence, gadolinium compounds have been regarded as ideal test benches for studying exchange interactions, free from complications due to crystal field effects. Large spontaneous magnetoelastic effects are frequently associated with rare earth compounds in which crystal fields are operative and in which the rare earth moments also have an orbital contribution. Surprisingly, equally large spontaneous magnetoelastic effects have been observed in some Gd compounds, showing that the contribution of the exchange interaction to spontaneous magnetoelastic effects can become of equal importance as the crystal field contribution. In several of the Gd compounds so-called magnetostructural transitions occur where giant spontaneous as well as forced magnetoelastic effects can be correlated with structural transitions. In Chapter 4 a review is given of experimental
studies of spontaneous magnetoelastic effects in Gd compounds, offering the possibility to estimate the relative contribution of exchange striction to the total spontaneous magnetoelastic effects in materials where also crystal field related contributions are present.
Volume 14 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 14 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.Y. , and I wish to thank Paul Penman for his great help and expertise.
Preface to Volume 14.
Contents.
Contents of Volumes 1-13.
List of Contributors.
II-V Ferromagnetic Semiconductors.
Magnetoelasticity in Nanoscale Heterogeneous Magnetic Materials.
Magnetic and Superconducting Properties of Rare Earth Borocarbides of the Type RNi2B2C.
Spontaneous Magnetoelastic Effects in Gadolinium Compounds.
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 cross-section 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 14 of this Handbook series.
Magnetoelectronics is a novel and rapidly developing field, where new functionalities are created by combining and utilizing simultaneously two degrees of freedom, the charge and the spin of the carriers. This new field is frequently referred to as spinelectronics or spintronics. It includes spin-utilizing devices that need neither a magnetic field nor magnetic materials. In semiconductor devices, the spin of the carriers has only played a very modest role so far because well established semiconductor devices are non-magnetic and show only negligible effects of spin. However, interesting enhanced spin-related phenomena were observed in magnetic semiconductors and diluted magnetic semiconductors already many years ago. A review of diluted magnetic semiconductors has been presented by Kossut and Dobrowolski in Volume
7. In a way compatible with the present-day electronic materials, diluted magnetic semiconductors can be prepared by introducing high concentrations of magnetic ions into the parent non-magnetic semiconductors. Semiconductors based on III-V compound are widely used for highspeed electronic devices as well as for optoelectronic devices. Moreover, heterostructures based on the GaAs/(Al,Ga)As systems have proven to be a convenient testing ground for novel physical concepts and devices. The introduction of magnetism into 111-Vcompounds therefore, opens up the possibility of using a variety of magnetic and/or spin-dependent phenomena. not present in the conventional non-magnetic parent compounds. Preparation and properties of ferromagnetic III-V based semiconductors are reviewed in Chapter 1, including heterostructures.
Nanoscale thin films and multilayers, nanocrystalline magnetic materials, granular films, and amorphous alloys have attracted much attention in the last few decades, in the field of basic research as well as in the broader field of materials science. Such heterogeneous materials display uncommon magnetic properties that virtually do not occur in bulk materials. This is true, in particular with respect to surface (interface) magnetic anisotropy and surface (interface) magnetostrictive strains and giant magnetoresistance. The local atomic arrangement at the interface differs strongly from that in the bulk. The local symmetry is lowered, so that some interactions are changed or are missing altogether. The interface atoms may be envisaged as forming a new phase and some properties characteristic of this phase may become predominant for the entire system. This becomes particularly evident in the case of interfacial magnetostriction which can lead to a decrease (almost to zero) or to an increase (over the bulk value) of the resulting magnetostriction of the nanoscale system. In Chapter 2 of the present Volume, the magnetoelasticity of heterogeneous materials is treated in much details. Generally, the dimensions of a magnetostrictive material change when the material is subjected to a change in magnetic field. Hence, magnetostrictive materials can be applied in transducers, which directly convert electrical energy into mechanical energy. They are useful in the manufacture of sensors, actuators, controllers, force and displacement as well as other electro-acoustic devices. For these applications, transducer materials in the form of thin films are of special interest because cost-effective mass production is possible, compatible to microsystem processing technologies. In addition, magnetostrictive thin films are particularly promising as microactuator elements like cantilevers or membranes, since they combine high-energy output, high-frequency and remote-control operation. Due to this potential, interest in such giant magnetostrictive thin films has rapidly grown over the past few years and results are reviewed in this Chapter
2. This chapter is a logical
extension of previous wok on magneto-elastic effects published in this handbook series over the years. Bulk giant magnetostrictive materials based on rare-earth compounds were reviewed by Clark (Volume I), quadrupolar interactions and magneto-elastic effects in rare-earth intermetallics were treated by Morin and Schmitt (Volume 5) and thermal expansion anomalies and spontaneous magnetostriction of these compounds were reviewed by Andreev (Volume 8).
There are various forms of the interplay of magnetism and superconductivity, which can be divided into competition and coexistence phenomena. For instance, a strong competition is found in high-Te cuprates. In these materials, depending on the doping rate, either Neel-type antiferromagnetism or superconductivity may occur, both based on the copper d-electrons. A coexistence of localized magnetic moments (e.g. from 4f-elements) with superconductivity is known to occur in systems where the concentration of these moments is sufficiently small or where they are antiferromagnetically ordered and only weakly coupled to the conduction electrons. A review on the interplay of magnetism and superconductivity in various types of intermetallic compounds has been presented by Fischer in Volume 5 of the Handbook. An extensive review on the normal state
magnetic properties of cuprate high-temperature superconductors and related materials has been presented by Johnston in Volume
10. A striking feature distinguishing the superconducting RT2B2C compounds from other superconductors is the following: For certain combinations of the R and T elements superconductivity and antiferromagnetic order have been found to coexist and more importantly, the values of the magnetic ordering temperature TN are comparable in magnitude with the values of the superconducting transition temperatures Te . This means that the magnetic energy is comparable with the superconducting condensation energy. Therefore the investigation of these compounds is expected to result in new insights into the interplay between superconductivity and magnetism. The high values of T ~ demand that in the quateary borocarbides, different
from the situation in high-Tc cuprates and the classical magnetic superconductors, the exchange coupling between the rare-earth magnetic moments is the dominant magnetic interaction rather than magnetostatic interaction. Obviously the exchange coupling is mediated by the conduction electrons, Consequently also the interaction between the magnetic moments and the conduction electrons must be relatively strong in the quateary borocarbides. A comprehensive review on the current status of research of the quateary borocarbide superconductors, starting from their discovery, is presented in Chapter 3 of this Volume. For the reasons mentioned, the magnetic and as well as the superconducting properties of this interesting class of materials is discussed together.
During the years, intermetallic gadolinium compounds have adopted a special position in the study of 4f electron magnetism. The reason for this is the fact that the gadolinium moment consists only of a pure spin moment, orbital contributions to the moment being absent. As a consequence, gadolinium compounds have been regarded as ideal test benches for studying exchange interactions, free from complications due to crystal field effects. Large spontaneous magnetoelastic effects are frequently associated with rare earth compounds in which crystal fields are operative and in which the rare earth moments also have an orbital contribution. Surprisingly, equally large spontaneous magnetoelastic effects have been observed in some Gd compounds, showing that the contribution of the exchange interaction to spontaneous magnetoelastic effects can become of equal importance as the crystal field contribution. In several of the Gd compounds so-called magnetostructural transitions occur where giant spontaneous as well as forced magnetoelastic effects can be correlated with structural transitions. In Chapter 4 a review is given of experimental
studies of spontaneous magnetoelastic effects in Gd compounds, offering the possibility to estimate the relative contribution of exchange striction to the total spontaneous magnetoelastic effects in materials where also crystal field related contributions are present.
Volume 14 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 14 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.Y. , and I wish to thank Paul Penman for his great help and expertise.
Preface to Volume 14.
Contents.
Contents of Volumes 1-13.
List of Contributors.
II-V Ferromagnetic Semiconductors.
Magnetoelasticity in Nanoscale Heterogeneous Magnetic Materials.
Magnetic and Superconducting Properties of Rare Earth Borocarbides of the Type RNi2B2C.
Spontaneous Magnetoelastic Effects in Gadolinium Compounds.
Author Index.
Subject Index.
Materials Index.