MAGNETIC PHASE TRANSITIONS IN THIN FILMS OF SOME LANTHANOIDS

Ján Dudáš

   Thin films of dysprosium, samarium and thulium were evaporated in a high vacuum approx 10^-4 Pa (Dy, Sm) and in ultrahigh vacuum approx 10^-7 Pa (Tm). Electrical resistance of these films has been investigated in temperature interval from 4.2 K up to the room temperature and in thickness range from 16 nm to 360 nm. The magnetic phase transition temperatures of Dy, Sm and Tm films were derived from the resistance versus temperature dependences. The N‚el temperature of all studied films is lower than of reference bulk samples of Dy, Sm and Tm. The T_C values of Dy, Tm and Sm films decreased with decreasing the film thickness. Two mechanisms could be responsible for such a behaviour - the increasing relative content of impurities and relative increase of the internal stresses with decreasing the film thickness. The thickness dependence of the residual resistance ratio suggests the importance of the impurity content on observed T_C versus t dependences.

Keywords: magnetic phase transitions, electrical resistivity, dysprosium, samarium and thulium thin films, low temperatures

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