Magnetism of YMn6Sn6 and DyMn6Ge6: Single-crystal Study
The magnetic properties of YMn6Sn6 and DyMn6Ge6, which crystallize in the hexagonal HfFe6Ge6-type of structure, have been studied on single crystals that have been prepared in an Sn flux and In flux, respectively. The compounds order antiferromagnetically at about 330 K and 450 K and exhibit very complex magnetic properties in the magnetically ordered state. The evolution of the magnetization in the ordered state has been investigated in the temperature region from 2 to 550 K and magnetic field up to 14 T.
Magnetic properties of rare-earth manganese compounds of the RMn6Ge6 type
Abstract We determined the magnetic properties of several compounds of the type RMn 6 Ge 6 (R is a heavy rare-earth element). Several of these compounds give rise to two ordering temperatures associated with antiferromagnetic ordering of the R and Mn sublattices. For GdMn 6 Sn 6 and to some extent also for TbMn 6 Sn 6 we observed magnetic behaviour which can be described as “bootstrap ferrimagnetism”: the antiferromagnetic configurations within both the R and Mn sublattices are broken simultaneously by the R-Mn intersublattice interaction, leading to ferrimagnetic alignment of the R and Mn sublattices. This bootstrap mechanism is sufficiently strong only if the intrasublattice Mn-Mn interaction is sufficiently weak. This condition is met only when the unit cell volume is sufficiently large. The interplay between intersublattice coupling and unit cell volume leads to interesting temperature dependences of the magnetization. In the magnetic isotherms the bootstrap mechanism leads to first-order phase transitions.
Evaluation of Lapping Grains based on Shape Characteristics.
The shape and size of abrasive grains during lapping varies complicately and irregularly. In this study, the aspect ratio of grain size and the fractal dimension of the grain external form were used as shape characteristics of grain in order to evaluate grains with lapping time. The results obtained are summarized as follows : (1)The fractal dimension increases due to microscopic fracture and decreases due to macroscopic fracture or attritious wear. (2)The aspect ratio and the fractal dimension, which are grain shape characteristicsis of the macroscopic shape and the microscopic surface complication of grain respectively, can be used for evaluating grain shape variation during lapping.