Controlling and modifying ferromagnet (FM) magnetization switching properties is of interest both due to its fundamental physical significance, and technological interests in high-density storage and sensor miniaturization. In addition to magnetic fields, FM switching can be also achieved by a spin-polarized electric current due to the spin transfer torque. Here we present a novel phenomenon in FM / AF heterostructure systems (AF=FeF{sub}2, FM=(Ni, Co)), where the FM switching can be also controlled by thermal cycling. We found that a FM saturated above the AF Neel temperature T{sub}N, spontaneously reverses its magnetization against a constant field with decreasing temperature. This reversal also exhibits a significant magnetization vs. temperature hysteresis, with a tunable height and width by the field. This is reminiscent of the conventional magnetization hysteresis and enables one to control the FM switching by thermal cycles, and may have implication on the thermally assisted magnetic recording.
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