Ionization of noble gases by strong infrared circularly-polarized laser pulses can produce electron currents with a controllable degree of spin polarization [1-4]. Spin polarization arises as a consequence of (1) entanglement between the liberated electron and the parent ion, and (2) sensitivity of ionization to the sense of electron rotation in the initial state. In this context, the use of two-color counter-rotating bicircular fields [5] opens new opportunities for introducing the spin degree of freedom into attosecond science [6], since the liberated electrons can be driven back towards the ionic core within one optical cycle.