Device for holding and releasing a sample holder is provided. The device includes a support member having a pin with a magnet at its free end for holding the sample holder, tubular body mounted on the support member around and along the pin, and a tubular guide movably mounted inside the body and able to occupy a releasing position where its outer end surrounds the magnet, and a holding position where the guide is retracted inwards the body so that the magnet holds the sample holder. A cam on the guide cooperated with a cam follower-movably through the body upon movement of the guide and with elastic biasing the guide towards its releasing position, to reversibly lock the follower in the holding position when the guide is moved inwards toward the body and to retrieve the initial releasing position, after further moving the guide inwards and releasing this movement.