Multiple First Order Transitions in Cr Thin Films

The incommensurate spin density wave (SDW) in metalic Cr forms below T_N = 311K and is characterized by a temperature dependent wave-vector Q along the <100> direction. The wavelength varies from 78 Å at 300 K to 60 Å at 150 K. In thin films, the Q-vector orients perpendicular to the film surface and the SDW is forced to satisfy boundary conditions. As a consequence of the confinement, the SDW wavelength is quantized in a set of available modes, each one having n nodes. As the temperature decreases the wavelength does not follow a continuous bulk-type variation but jumps between different allowed values. These jumps occur at certain determined temperatures T_n as first order type transitions which are accompanied with a decrease (n to n + 1 nodes) or an increase (n + 1 to n nodes) of the resistance. In this work, we present transport measurements on Cr thin films showing hysteretic behavior in the resistance as a function of temperature in cooling-warming cycles. The hysteresis loops are thickness dependent and present structures which we associate with the possible multiple transitions that may occur as temperature is swept.