A film with this property pins the top film of permalloy (“perm-alloy”) in valve-like devices used as hard-drive read heads. Doping the insulator LaMnO3 with calcium or strontium causes it to [emphasize] stop exhibiting this phenomenon and become highly conductive. The first conclusive evidence of a material exhibiting this phenomenon came from Clifford Shull and Samuel Smart’s neutron diffraction experiment. In an archetypal example of this phenomenon, it arises because d electrons partially occupy the antibonding orbital of a Mn–O–Mn chain, and thus the manganese ions can interact across oxygen via superexchange. Uniquely, chromium exhibits this phenomenon at room temperature. In materials exhibiting this phenomenon, susceptibility increases with temperature up to the Néel (“NAY-el”) temperature. For 10 points, name this phenomenon in which neighboring spins point in opposite directions. ■END■
ANSWER: antiferromagnetism [or antiferromagnetic materials; prompt on magnetism or magnetic materials or materials with magnetic ordering; reject “ferromagnetism,” “diamagnetism,” “paramagnetism,” or any other more specific forms of magnetism] (The first sentence refers to spin valves.)
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