Hard magnets Subject

The rare earth-cohalt magnets are discussed here with a fairly applied bias. Relevant fundamental subjects are treated exhaustively elsewhere in this handbook series basic magnetic properties of the RE-elements by Legvold (1980), those of RE-TM intermetallics by Buschow (1980), and the theory of hard-magnetic behavior - small-particle magnetization reversal, domain-wall nucleation and motion, and the role of anisotropy in these - by Zijlstra (1982). Buschow (1988) discusses the various mechanisms thought to be controlling the coercivity in all REPM, and the... 

The acceptance of optical data storage iato the mass storage market, which is as yet exclusively dominated by magnetic systems, will be fundamentally boosted if optical drives and media are subject to uniform standards and become fully compatible, and multiuser drives are offered which enable the user to employ alternatively CD-ROM and EOD disks, and maybe WORM disks as well (and CD-R disks, respectively). A prerequisite, however, will be whether rewritable optical memories will use the MOR or the PCR process. This accord especially will be hard to reach. 

Tribology performances and applications of ordered molecular films have been a long-standing research subject in SKLT, the workplace for the authors of this book. Hu and Luo [42] prepared SAMs of fluoroalkylsilane (FAS) and poly-fluorealkylmethacrylate (PFAM) on the magnetic head of computer hard disk drivers. Experiment results show that the molecular films greatly improve the performance of the... 

A hard disk typically consists of an Al-Mg alloy (or glass substrates), a NiP undercoat, magnetic layer, carbon overcoat, and a very thin layer of lubricant, as illustrated in Fig. 1.1. Since the Al-Mg alloy is mechanically soft, a hard undercoat is applied to provide adequate impact resistance to the head-disk interactions. The magnetic layer where the information is stored is typically sputtered directly onto a bare NiP/Al-Mg disk substrate. A carbon overcoat is sputtered to enhance wear and/or corrosion resistance. Finally, a molecularly thin layer of PFPEs (the subject of this chapter) along with airbearing is added to further reduce both the wear of the overcoat and stiction between the head and disk. 

Hard-disc drive heads are subjected to a heavier use and therefore need a different design in order to prevent wear and extend the useful life of both the disc and the head. Hard-disc drive heads (also known as Winchester heads) make no physical contact with the hard disc. They are designed to fly very close to the disc, supported by the air flow resulting from the disc rotation. Fig. 5.18. The magnetic element in Winchester heads is usually a Mn-Zn ferrite. 

The effect of an externally applied magnetic field on crystalline scale deposition, typically of CaCOs from hard water flowing in metal pipes, still remains a controversial subject despite the considerable number of investigations made over the past thirty years or so. There is still no general agreement on either the efficacy of commercially available devices or on the speculative mechanisms that have been proposed to explain their action (Sohnel and Mullin, 1988 Prasad et al., 1999 Kotsinaris et al., 1999). 

In this chapter the focus is upon electronic conductivity in perovskites. The electrons in perovskites are believed to be strongly correlated that is, they do not behave as a classical electron gas, but are the subject to electron-electron interactions. This leads to considerable modification of the collective electron behaviour of the conduction electrons, resulting in metal-insulator transitions, high-temperature superconductivity, half-metals and colossal magnetoresistance (CMR). The effects of strong correlation are important for the 3d, 4d and4f elements. In many ways the topics described here are thus a continuation of the previous chapter on magnetic perovskites, and in truth the two subject areas cannot be separated in a hard and fast maimer. 

Progress in the understanding of superionic conduction is due to the use of various advanced techniques (X-ray (neutron) diffuse scattering, Raman spectroscopy and a.c.-impedance spectroscopy) and-in the particular case of protons - neutron scattering, nuclear magnetic resonance, infrared spectroscopy and microwave dielectric relaxation appear to be the most powerful methods. A number of books about solid electrolytes published since 1976 hardly mention proton conductors and relatively few review papers, limited in scope, have appeared on this subject. Proton transfer across biological membranes has received considerable attention but is not considered here (see references for more details). 

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