|
|
Low-field excitations in magnetite
Švindrych, Zdeněk ; Janů, Zdeněk (advisor) ; Novák, Pavel (referee) ; Svoboda, Pavel (referee)
We have performed detailed measurements of magnetic and dielectric properties of high quality magnetite (Fe3O4) single crystals in weak magnetic and electric fields. These measurements can reveal details of phase transitions and other features that are not yet fully understood. We focused not only at the Verwey transition - a well known phase transition taking place at about 120 K in stoichiometric samples - but we also explored and described new relaxation effects in magnetite at low temperatures. The low-temperature properties were also found to be exceptionally sensitive to sample quality, stoichiometry and homogeneity. The results presented in this thesis were acquired on sensitive non-commercial SQUID magnetometer complemented by four-probe dielectric spectroscopy and dc conductivity measurements.
|
|
| |
|
|
Low-field excitations in magnetite
Švindrych, Zdeněk ; Janů, Zdeněk (advisor) ; Novák, Pavel (referee) ; Svoboda, Pavel (referee)
We have performed detailed measurements of magnetic and dielectric properties of high quality magnetite (Fe3O4) single crystals in weak magnetic and electric fields. These measurements can reveal details of phase transitions and other features that are not yet fully understood. We focused not only at the Verwey transition - a well known phase transition taking place at about 120 K in stoichiometric samples - but we also explored and described new relaxation effects in magnetite at low temperatures. The low-temperature properties were also found to be exceptionally sensitive to sample quality, stoichiometry and homogeneity. The results presented in this thesis were acquired on sensitive non-commercial SQUID magnetometer complemented by four-probe dielectric spectroscopy and dc conductivity measurements.
|
|
| |
|
| |
|
|
Kritický stav v tenkém Nb filmu
Youssef, A.E. ; Švindrych, Z. ; Hadač, J. ; Janů, Zdeněk
We present high resolution measurements of temperature dependence of low frequency ac magnetic susceptibility of superconducting Nb thin film in perpendicular time-varying periodic applied magnetic fields. We map this data, including harmonics, to the ac susceptibility calculated on basis of the complete analytical model of magnetization of thin superconducting disk in critical state. We find an excellent agreement between the measured and model data for temperatures up to 0.9997Tc
|
|
|
Magnetická studia fázových přechodů v magnetitu
Švindrych, Z. ; Janů, Zdeněk ; Hadač, J.
We have measured low field dc and low frequency ac magnetic properties of high quality magnetite single crystals with continuously reading high resolution SQUID magnetometer in a temperature range of 5 – 150 K. In these data several features can be observed: the anisotropy point around 130 K, Verwey transition near 122 K, glass-like transition around 40 K and finally anomalous magnetic behaviour at lowest temperatures (below 30 K).
|
guest ::
