Multiferroics (MF) based nanostructures combining ferroelectricity (FE) and antiferromagnetism (AF) are attracting a lot of interest in the scientific community . Indeed, a controlled magnetoelectric coupling in a single nanostructure will bring a direct way to control the magnetic state of the MF material . Therefore, MF materials are good candidates for use in nanodevices, like magnetic memories or high frequency devices [1][2][3] . However, most of MF materials possess a Néel temperature well below 300 K, reducing the number of candidates available for room temperature applications . Still, a good candidate for exchange coupling at room temperature is BiFeO 3 (BFO) . An interesting use of MF would be in MF/Ferromagnet exchange coupled bilayers as the net magnetization could then be controlled through the coupling by the use of an electric field . Such coupling named exchange bias was discovered by Meiklejohn and Bean [4] . It results in a characteristic horizontal shift of the hysteresis cycle (bias), and can be interpreted as unidirectional anisotropy . Previous studies carried out on epitaxial or bulk BFO have demonstrated the key role of the crystalline ordering (eg. the strain) for driving some of the multiferroic properties (eg. the presence of a magnetic cycloid) [5,6] . Furthermore, it is well known that the unidirectional anisotropy depends on structural disorder at the interface, which includes crystalline disorder . Therefore, it is of interest to study the exchange bias properties not only in epitaxial systems but also in polycrystalline ones . Following this, we have recently demonstrated that an exchange coupling may be induced in polycrystalline BiFeO 3 /Ni 80 Fe 20 (Py/BFO) bilayers [7,8] . At 300 K, the interfacial exchange coupling energy in the polycrystalline BFO/Py bilayers is similar to those reported in previously studied epitaxial BFO/F bilayers [9][10][11] . However, a temperature dependence study could reveal differences between epitaxial and polycrystalline systems . In this study, we report a temperature dependent analysis of the exchange bias properties in BFO/ Py bilayers as a function of the BFO thickness . The temperature dependence of the exchange bias field (H e ) and the coercive field (H c ) are first presented . To understand exchange bias magnetization reversal and the magnetic anisotropies, we will then present an azimuthal study of H e and H c at 300 K and 77 K . Finally, results of a controlled field cooling protocol applied on all samples will be discussed to understand anisotropy energy distribution . The bilayers were grown by radio-frequency sputter deposition, with the following structure: Si/Pt(14 nm)/BiFeO 3 (t BFO )/Ni 80 Fe 20 (10 nm)/ Pt(10 nm), with t BFO among 0 nm, 29 nm and 177 nm . To induce uniaxial anisotropy, a 300 Oe field H dep was applied during the growth . The XRD analysis confirmed a single polycrystalline structure for the BFO layer . To investigate the reversal mechanism, we measured the azimuthal magnetic behavior using a vectorial vibrating sa...