Magnetic ferrimagnetism

Magnets Ferrimagnetic Mixed-Valence Chroniium(in)-Chromium(II) Cyanides with TC = 240 and 190K, Science 262,1554,1993 b) M. Verdaguer - Molecular Electronics Eimerges in Molecular Magnetism,... 

Magnetorheological materials (fluids) are the magnetic equivalent of electrorheological fluids. In this case, the particles are either ferromagnetic or ferrimagnetic sohds that are either dispersed or suspended within a Hquid and the apphed field is magnetic (14). 

Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

The magnetic moments of the heavy RE elements (Gd, Tb, Dy, etc) are coupled antiparallel to the magnetic moments of the TM elements (Fe, Co, etc). The REj TM alloys are therefore ferrimagnetic below their Curie temperature (T )- The heavy TM moments form one magnetic sublattice and the RE moments the other one. In contrast, the light RE moments (eg, Nd, Pr) couple parallel to the moments of TM. The RE spia is always antiparallel to the TM spia, but for the light RE elements, the orbital momentum is coupled antiparallel to the spia and larger than the spia. 

Technical Magnetic Behavior. When a magnetic-field strength H is appHed to a ferromagnetic or ferrimagnetic material, the latter develops a flux density or iaduction as a result of orientation of the magnetic domains. The relation between B and H is... 

See p. 500 of ref. 24 for a description of Ihe garnet structure which is also adopted by inany. synthetic and non-silicaie coniponnds these have been much stndied recently becan.se of their important optical and magnetic properties, e.g. ferrimagnetic vitriuni iron garnet (YIG), y> Fe (Al" b4),. 

So-called hexagonal ferrites such as BaFe -Oi9 are ferrimagnetic and are used to construct permanent magnets. A third type of ferrimagnetic mixed oxides are the garnets, Mj FejOjj, of which the best known is yttrium iron garnet (YIG) used as a microwave filter in radar. 

When a magnetic field, B, is applied to a ferromagnetic or ferrimagnetic particle with magnetic moment, p, the magnetic energy has a contribution from the Zeeman term... 

Defects in ferrimagnetic structures often lead to noncollinear (canted) spin structures. For example, a diamagnetic substitution or a cation vacancy can result in magnetic frustration which leads to spin-canting such that a spin may form an angle 6c with the collinear spins in the sample [80, 81]. Similarly, the reduced number of neighbor ions at the surface can also lead to spin-canting [80-83]. 

In yttrium iron garnet Y3Fe5012 ( YIG ) a ferrimagnetic coupling (superexchange) is active between the octahedral and the tetrahedral sites. Since the tetrahedral sites are in excess, the magnetic moments do not compensate each other. The magnetic properties can be varied by substitution of yttrium by lanthanoids. 

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