A method of manufacturing a magnetic field sensor having a stacked structure which comprises: a substrate (1); an exchange-biasing layer (2) comprising nickel oxide; a magnetic layer (3) which is exchange-biased with the exchange-biasing layer (2), whereby at least the exchange-biasing layer (2) is provided by sputter deposition using a sputter gas which comprises Ne and/or He. The magnetic layer (3) preferably comprises permalloy. In a particular embodiment, the magnetic layer (3) is separated from a second magnetic layer (5) by an interposed non-magnetic layer (4), so as to form a spin-valve trilayer.