Nanocomposite films of ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/{\mathrm{Ni}}_x{\mathrm{Fe}}_{\text{1−x}}\mathrm{O}$ were prepared by a dual ion-beam deposition technique. The structural and magnetic properties of nanocomposite films fabricated with oxygen content in the deposition assist beam ranging from 0% to 55% were studied. The dependence of the resistivity on oxygen percent shows that the compositions with exchange-enhanced coercivity are close to a percolation threshold. A strong temperature dependence of coercivity $H_c$ and exchange bias field $H_{\mathrm{ex}}$ is found in these composite films. Films prepared with 46% ${\mathrm{O}}_2$ in the assist beam exhibit an enhanced $H_c$ relative to Permalloy $({\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20})$ and a characteristic shifted hysteresis loop indicative of exchange coupling between the constituent metal and oxide phases. At $\text{T=10\hspace{0.17em}}\mathrm{K},$ films prepared with 44% ${\mathrm{O}}_2$ in the assist beam have an exchange shift $H_{\mathrm{ex}}\text{∼−225\hspace{0.17em}}\mathrm{Oe}$ with a blocking temperature $T_B\text{∼100\hspace{0.17em}}\mathrm{K}$ that reflects the low Néel temperatures of FeO-rich ${\mathrm{Ni}}_x{\mathrm{Fe}}_{\text{1−x}}\mathrm{O}$ solid solutions.

The correlation between the ion-beam bombardment and the exchange bias magnetism in NiFe (10 nm)/Mn (25 nm) bilayers was studied. While the bottom Mn layers bombarded by different Ar ion-beam energies ($V_{\text{EH}}$ from 70 to 150 V) retained the same structure, significant differences in exchange bias were observed when in contact with a top NiFe layer. The dependence of the exchange bias field, $H_{\text{ex}}$ , with increasing $V_{\text{EH}}$ suggests strongly that the Ar ion-beam bombardment process may create uncompensated Mn spins ($H_{\text{ex}}$ enhancement) or increase the spin misalignment in ferromagnet (FM)/antiferromagnet (AF) interfaces ($H_{\text{ex}}$ decrease), depending on the energy used. A schematic FM/AF spin structure was proposed to explain this unusual exchange bias behavior.

The structural and magnetic properties of $\mathrm{Ni}\mathrm{Co}∕(\mathrm{Ni},\mathrm{Co})\mathrm{O}$ bilayers were investigated. X-ray diffractometry results have shown that the top NiCo layer consisted of a fcc NiCo phase. The bilayer bottom was either a pure (Ni,Co)O or a composite $[\mathrm{Ni}\mathrm{Co}+(\mathrm{Ni},\mathrm{Co})\mathrm{O}]$ phase, depending on the percent of ${\mathrm{O}}_2∕\mathrm{Ar}$ ratio used during deposition. A double-shifted hysteresis loop exhibiting components that were from positive or negative coupling was observed in the $\mathrm{Ni}\mathrm{Co}∕(\mathrm{Ni},\mathrm{Co})\mathrm{O}$ $(8\%{\mathrm{O}}_2∕\mathrm{Ar})$ bilayers. The microstructural changes, which result from a combination of deposition oxygen content and the ion-beam bombardment, will result in the unusual exchange bias behavior.

A series of ferromagnetic Ni80Fe20(55 nm)/antiferromagnetic CoO (25 to 200 nm)/ferromagnetic Co (55 nm)/SiO2(substrate) trilayer thin films were fabricated by ion-beam assisted deposition in order to understand the role of ion beam modification on the interfacial and interlayer coupling. The microstructural study using transmission electron microscopy, X-ray reflectometry, and polarised neutron reflectometry showed that ion-beam modification during the deposition process led to an oxygen-rich Co/CoO nanocomposite interface region at the bottom layer. This interface caused a high exchange bias field for the ferromagnetic cobalt. However, the exchange bias for top permalloy ferromagnet remained low, in line with expectations from the literature for the typical interfacial energy. This suggest that the ion-beam enhancement of the magnetic exchange bias is localized to the Co/CoO interface where local microstructural effects provide the dominant mechanism.