I created a function where I access to a Raster folder and get all files CRS

            for Rsubdir, Rdirs, Rfiles in os.walk(Rrootdir):  
                for Rfile in Rfiles:
                    Rfile, Rextension = os.path.splitext(os.path.join(Rsubdir, Rfile).replace("\\", "/"))
                    if Rextension == '.tif':  
                        RfileName = os.path.join(Rsubdir, Rfile).replace("\\", "/") + ".tif"
                        if os.path.isfile(RfileName):
                            RfileInfo = QFileInfo(RfileName)
                            RbaseName = RfileInfo.baseName()
                            Rlyr = QgsRasterLayer(RfileName,RbaseName) 
                            coordR=Rlyr.crs().authid()
                            RasterCRS.append(coordR)

the problem is when I try to access the same folder files after this function call, I get a PermissionError

PermissionError: [WinError 32] Le processus ne peut pas accéder au fichier car ce fichier est utilisé par un autre processus: 'chemin_fichier.tif'

which means that the files are always opened. is there any way to close them in the end of the function?