Detection of field-dependent antiferromagnetic domains in exchange-biased Fe3O4/NiO superlattices

Abstract

Neutron diffraction studies of Fe3O4/NiO superlattices reveal that the field dependence of domains in the antiferromagnetic NiO is correlated with the presence or absence of exchange biasing. Measurements of the full width at half maximum of the (111) NiO reflection show that after cooling in zero field, the antiferromagnetic domain size both parallel and perpendicular to the growth axis is sensitive to the strength of the applied field. In contrast, after cooling from room temperature in a field of 5 T, the domain size is generally smaller than the zero-field-cooled value and does not vary with field. These data suggest that exchange biasing originates from domain walls frozen into the antiferromagnet upon field cooling.

Training of the exchange-bias effect in NiO-Fe heterostructures

“…AF domain states have been extensively studied in the case of NiO. [12][13][14][15][16][17][18] Indeed, we observe a distinct training effect when depositing a thin Fe layer on top of the compensated ͑001͒ surface of a NiO single crystal.…”

Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins inNi81Fe19∕α‐Fe2O3Dho1, Leung2, Barber3 et al. 2005Phys. Rev. B241190View full textAdd to dashboardCite

“…This exchange bias is fundamental to the operation of spin valve devices such as magnetic read-heads, nonvolatile memories, and various sensors [2][3][4]. Despite considerable work by many groups over the past two decades, the origin of the exchange bias and the enhanced coercivity are still unclear [5][6][7][8]. One of the primary aims of the various models is the reconciliation of the experimentally observed values of H ex and H C with theoretical predictions.…”

“…The form of the spin flop coupling is comparable with the classical uniaxial anisotropy energy, and thus the coercivity is mainly dependent on the second term of (1). If we associate exchange bias with a domain wall formed in the AF layer [7,10,27], its stability is determined by a competition between a decrement of direct coupling energy and an increment of the AF anisotropy energy. From equation (1), we expect that a magnetic field annealing (MFA) process perpendicular to the AF spin direction will stabilize the spin-flop coupling, and in turn it will enhance the coercivity.…”

Training of the exchange-bias effect: A simple analytic approach

“…AF domain states have been extensively studied, for instance, in the case of NiO. [11][12][13][14][15][16][17] In fact, it has been recently shown, that the total magnetic moment of a NiO͑001͒ /Fe͑110͒ heterostructure is reduced with consecutively cycled hysteresis loops. 18,19 Since the FM top layer of the AF/ FM heterostructure is saturated after each loop, it is obvious, that the successive reduction of the magnetic moment takes place in the AF pinning component.…”