Is expiation obligatory for a wife who swore that she and her husband would not buy electronic devices for their children, and then her husband forgot and bought some?

If a person makes another swear not to do something, and the one who swore breaks the oath, then expiation is incumbent upon the one who made the oath, not upon the one who swore, and this is by agreement of the majority of jurists. If the one who swore breaks the oath out of forgetfulness, then there is no expiation upon the one who made the oath; because forgetfulness is excused in Islamic law, and there is no sin in it, and expiation was legislated to remove the sin of breaking an oath.