Quantum fluctuation and the magnetically structural symmetry in ferrimagnetic superlattices

摘要

The magnetization and the quantum fluctuations in several ferrimagnetic superlattices consisting of 2-6 different magnetic sublayers are studied by employing Holstein-Primakoff transformations and Green's functions technique only for zero temperature. Investigating ferrimagnetic superlattices with different magnetic sublayers and different spin configurations, we find that when some of spin quantum numbers are adjusted, some sublayer magnetizations at zero-temperature exhibit a minimum, correspondingly, the quantum fluctuation of the system exhibits a maximum point. Different spin configurations have different quantum fluctuations of the system. The maximum point of the quantum fluctuation of the system is related with higher symmetry of the system. It differs from the symmetry of crystallographic point-groups or space-groups, but belongs to the type III Shubnikou group of magnetic group, which describes anti-ferromagnetic or ferrimagnetic state. We define it as the magnetically structural symmetry. The higher the magnetically structural symmetry of the system is, the stronger the quantum fluctuation of the system is, for varying spin quantum numbers and different spin configurations. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.