The husband in 'The Necklace' is a 'thrifty clerk' who doesn't like to spend too much money. After implored by his wife, he gives her the money that he saved up for a rifle so she could buy a nice dress instead. The husband in 'The Gift of the Magi' is not cheap and is willing to spend all it takes to please his wife.
The wife in 'The Necklace' is one Mathilde Loisel who longs to be a member of 'high society'. She thinks herself poor, though she has a servant and is too blinded by her dream to take notice and appreciate the things she does have. Though she is accustomed to a life of leisure, she does work hard when she has to. In 'The Gift of the Magi', Della, the wife, actually does live in poverty but she's content with this as long as she and her husband are happy. She is willing to do what it takes in order to keep the latter happy.
The irony in 'The Necklace' becomes apparent as the very item that had brought Mathilde's dream of 'high living' to life was her and her husband's eventual downfall. Mathilde loses the 'diamond' necklace which she borrowed from her friend and the couple are forced to work for ten years to pay in full the debt they developed after buying a replacement. As it is revealed in the end by Mathilde's friend (from whom she borrowed the necklace) it was actually made of a paste, a cheap substance that has the luster of diamond. In 'The Gift of the Magi', Della forgoes her most prized possession, her long hair, in order to buy her husband, Jim, a Christmas present, a chain to accompany his gold watch which is purpoted that even King Solomon would be jealous of. The irony here is that Jim sells his most prized possession, his golden watch (the very same that Della bought the chain