Effect of anisotropy on the critical antiferromagnet thickness in exchange-biased bilayers

Physical Review B, 2003

An analytical model of exchange anisotropy in epitaxial ferromagnetic/antiferromagnetic bilayers was developed. The model demonstrates that the high symmetry exchange anisotropy terms in ferromagnetic/ antiferromagnetic bilayers originate from a partial domain wall in the antiferromagnetic layer. Application of the model to the experimental data analysis enables one to separately determine the fraction of uncompensated interfacial spins in the antiferromagnetic layer and the interfacial exchange coupling energy between spins in the ferromagnet and in the antiferromagnet. The model provides a quantitative description of complex exchange anisotropy recently observed in Fe/MnF 2 bilayers.

Physical Review B, 2002

The angular dependence of the magnetic anisotropy of exchange biased Fe/MnF 2 bilayers was measured. Below the Néel temperature of the antiferromagnetic MnF 2 layer, an exchange anisotropy is observed which consists of unidirectional, uniaxial, threefold and fourfold symmetry components. The threefold exchange anisotropy term is responsible for the asymmetric magnetization reversal process recently observed in this system.

Applied Physics Letters, 1996

Large exchange bias effects (ΔE∼1.1 erg/cm2) were observed in antiferromagnetic (FeF2)–ferromagnetic (Fe) bilayers grown on MgO. The FeF2 grows along the spin-compensated (110) direction. The FeF2–Fe interface roughness was characterized using specular and diffuse x-ray diffraction and atomic force microscopy. The magnitude of the exchange bias field HE increases as the interface roughness decreases. These results imply that magnetic domain creation in the antiferromagnet plays an important role.

Journal of Magnetism and Magnetic Materials, 2005

We study a series of NiFe ð10:0 nmÞ=½Ir 20 Mn 80 ð6:0 nmÞ=Co 80 Fe 20 ð3:0 nmÞ N multilayers with different numbers N of bilayers grown by DC magnetron sputtering. After field-cooling, SQUID and MOKE measurements show a sizable increase of the exchange bias field with N. X-ray specular and diffuse scattering data reveal no significant variation of the lateral correlation length and only a weak dependence of the vertical rms interface roughness on N. Atomic and magnetic force microscopy, however, show a strong reduction of the grain size accompanied by distinct changes of the magnetic domain structure. We conclude that the enhancement of the exchange bias effect is related to the shrinking of the domain size in the antiferromagnet due to the structural evolution in the multilayers. r

Journal of Physics D: Applied Physics, 2006

The influence of an imperfect interface on exchange bias (EB) properties is investigated. Within the framework of the domain state model, the EB field H EB and the coercive field H C are determined using computer simulations, and they are found to depend strongly on the details of the interface structure. This dependence is sensitive to the dilution of the antiferromagnet (AFM) with non-magnetic defects in the bulk. For the optimal interface structure, giving greatest EB, the optimal dilution is found to be much less than that for an ideal-interface system, taking a value in better agreement with experimental results. Even without any defects in the bulk of the AFM the interface roughness leads to EB for thin antiferromagnetic layers, in accordance with the model by Malozemoff. Finally, the thickness dependence of rough-interface systems is found to differ significantly from that of ideal-interface systems.

Physical Review B, 2002

We have undertaken a systematic study of the influence of in-plane crystalline quality of the antiferromagnet on exchange bias. Polarized neutron reflectometry and magnetometry were used to determine the anisotropies of polycrystalline ferromagnetic ͑F͒ Fe thin films exchange coupled to antiferromagnetic ͑AF͒ untwinned single crystal ͑110͒ FeF 2 , twinned single crystal ͑110͒ FeF 2 thin films and ͑110͒ textured polycrystalline FeF 2 thin films. A correlation between the anisotropies of the AF and F thin films with exchange bias was identified. Specifically, when exchange coupling across the F-AF interface introduces an additional anisotropy axis in the F thin film-one perpendicular to the cooling field, the magnetization reversal mechanism is affected ͑as observed with neutron scattering͒ and exchange bias is significantly enhanced.

Physical Review B, 2008

Using neutron diffraction, we measured the sizes of antiferromagnetic domains in three ferromagnet/ antiferromagnet bilayer samples as a function of the magnitude and sign of exchange bias, temperature, and antiferromagnet composition. Neutron-scattering techniques were applied to thin films with masses less than 10 g. We found the antiferromagnetic domain size to be consistently small regardless of the exchange bias. For a Co/untwinned single crystalline antiferromagnet ͑AF͒-fluoride bilayer, the antiferromagnetic domain size is comparable to the crystallographic domain size of the AF. For one sample the highest temperature at which the exchange bias was nonzero ͑i.e., the blocking temperature͒ was suppressed by ϳ3 K compared to the Néel temperature of the antiferromagnet.

The exchange bias phenomenon in bilayered and trilayered thin films, based on NiFe and IrMn, was studied. The exchange bias and coercivity fields dependences on the antiferromagnetic layer thickness were obtained. It was shown that 6 nm of IrMn is a critical thickness for the exchange bias appearance. Largest value of the exchange bias is found to be for NiFe/IrMn/NiFe sample with 10 nm thickness of antiferromagnetic layer.

Physics Procedia, 2015

The influence of the antiferromagnetic layer thickness on the magnetic properties of the trilayered thin-film structures with the exchange bias phenomenon was studied in the temperature range from 100 up to 295 K. Dependences of the coercive force and exchange bias field on AF-layer thickness were analyzed for all structures with AF layer thickness from 2 nm up to 50 nm at room and low temperatures. The explanation in terms of the anisotropy and thermal energies competition was given for disclosure of an exchange bias for structures with 2 nm AF layer thickness at low temperatures.

Physical Review Letters, 2007

Fe=Mn is a model system in which to study exchange bias, since the antiferromagnetic (AF) Mn layers are believed to have uncompensated moments with all spins aligned in the plane and parallel to those of the Fe. We have determined the microscopic AF ordering at the interfaces using single-crystal neutron diffraction. An unexpected magnetic structure is obtained, with out-of-plane Mn moments perpendicular to those of Fe. This explains the low bias field and shows that the simple AF ordering assumed in a variety of exchange-biased systems may well have to be revised.