Magnetic properties of Ho2Fe17-xMnx - Influence of Mn substitution
The structural and magnetic properties of Ho2Fe17−xMnx (x=0−5) have been investigated by x-ray diffraction, Mossbauer spectroscopy and DC magnetization measurements (0-5 T) over the temperature range 4.5–350 K. Similar to other ferrimagnetic R2Fe17−xMnx systems, the unit cell volume generally increases with Mn content other than for low Mn values where a slight maximum is detected around x ~ 0.5. The nature of the magnetic phase transitions around TC is shown by Arrot plot analysis to be second order for all samples. The Curie temperature remains essentially unchanged for Mn contents up to x=1.0 (TC = 336 K for x=0.0, TC = 338 K for x=1.0) before decreasing steadily with further increase in Mn content (TC = 209 K for x=5). The 57Fe hyperfine interaction parameters have been determined from variable temperature Mossbauer spectra.
Magnetovolume effect in Ho2Fe17-xMnx compounds
The structural and magnetic properties of seven compounds in the Ho2Fe17-xMnx series (x = 0-5) have been investigated. The spontaneous magnetization Ms at 10 K exhibits a minimum at x ≈ 3.8 while the 3d-sublattice magnetization MT is found to decrease at ∼ −3.4 μB/per Mn atom compared with the rate of ∼−2.0 μB/per Mn atom expected from a simple dilution model. All of the Ho2Fe17-xMnx compounds exhibit anisotropic thermal expansion below their Curie temperatures leading to the presence of strong magnetovolume effects and Invar-type behavior below TC. An approximately zero volume thermal expansion has been detected between 10 K and 270 K for Ho2Fe17. The maximum magnetic entropy changes for Ho2Fe17-xMnx with x = 0 and 2.0 are 3.2 J kg−1 K−1 around TC ∼ 336 K and 2.7 J kg−1 K−1 around TC ∼ 302 K, respectively, for magnetic field change of B = 0-5 T.
Mathematical Time and Physical Time in the Theory Of Relativity
In the Theory of Relativity time is an imaginary quantity that can not be observed; it is a multiplication of a number that indicates duration of material change and number i that is an imaginary number. i on the square is -1. Time i⁄t is a mathematical time that describes the speed and the duration of material change. In the Universe one can observe physical time only as a stream of material change. It is not that change run in physical time, change itself is physical time.. Distinction between imaginary mathematical time and visible physical time opens some new perspectives into interpretation of Theory of Relativity. c