The present disclosure relates to, inter alia, devices, systems, and methods for use in the magnetic separation of biological entities from fluid samples. This device includes a magnetic separation chamber configured to receive a fluid sample for magnetic separation, where the magnetic separation chamber includes at least two magnets mounted on the surface or in the wall of the magnetic separation chamber. The device also includes a force provider configured to move the magnetic separation chamber in a side-to-side motion to mix and/or magnetize the fluid sample. In one embodiment, the magnetic separation chamber is in a form of a sleeve and comprises a substantially central channel for loading a vessel containing the fluid sample therein. The systems and methods of the present disclosure involve the use of this device to separate biological entities from fluid samples.