Spin-paramagnetic transition of ultrathin granular Al films in a tilted magnetic field

Wenhao Wu, Louisiana State University
R. G. Goodrich, Louisiana State University
P. W. Adams, Louisiana State University


We report measurements of the critical fields of ultrathin granular Al films as a function of temperature and magnetic-field orientation. Due to the spin-paramagnetic effect, the parallel field (θ=0°) transition becomes first-order and strongly hysteretic below a tricritical point, Ttri∼270 mK. Well below Ttri, the width of the hysteresis collapses according to ΔH(θ)=ΔH(0°)exp(-θ/2.4°) with increasing θ. Our data suggest that the zero-temperature transition goes from first order to second order at θ6.5°. © 1995 The American Physical Society.