Spinel ferrite NiFe O thin films have been grown on three isostructural substrates, MgAl O , MgGa O , and CoGa O using pulsed laser deposition. These substrates have lattice mismatches of 3.1%, 0.8%, and 0.2%, respectively, with NiFe O . As expected, the films grown on MgAl O substrate show the presence of the antiphase boundary defects. However, no antiphase boundaries (APBs) are observed for films grown on near-lattice-matched substrates MgGa O and CoGa O . This demonstrates that by using isostructural and lattice-matched substrates, the formation of APBs can be avoided in NiFe O thin films. Consequently, static and dynamic magnetic properties comparable with the bulk can be realized. Initial results indicate similar improvements in film quality and magnetic properties due to the elimination of APBs in other members of the spinel ferrite family, such as Fe O and CoFe O , which have similar crystallographic structure and lattice constants as NiFe O .

We study the temperature-dependent static and dynamic magnetic properties of polycrystalline permalloy (Ni 80 Fe 20 , Py)/Gd bilayers using DC magnetometry and broadband ferromagnetic resonance. Magnetometry measurements reveal that the 3-nm-thick Gd layers undergo a magnetic ordering transition below 100 K, consistent with finite size suppression of their Curie temperature. Upon cooling below this Gd ordering temperature, ferromagnetic resonance spectroscopy reveals a sharp increase in both the gyromagnetic ratio (γ) and effective Gilbert damping parameter (α) of the neighboring Py layers. The increase of γ is attributed to the onset of strong antiferromagnetic coupling between the Gd and Py layers as the Gd orders magnetically. We argue that the increase of α, on the other hand, can be explained by spin pumping into the rare earth layer when taking into account the increase of γ, the decrease of the Gd spin diffusion length as it orders, and, most significantly, the corresponding increase of the Py/Gd interfacial spin mixing conductance in the vicinity of the magnetic ordering transition. We propose that these observations constitute a qualitative confirmation of a recent theoretical prediction of spin sinking enhancement in this situation.2

The magnetization dynamics of exchange biased IrMn/CoFe bilayers have been investigated using broadband and in-plane angle dependent ferromagnetic resonance spectroscopy. The interface energy of the exchange bias effect in these bilayers exceeds values previously reported for metallic antiferromagnets. A strong perpendicular magnetic anisotropy and a small in-plane uniaxial anisotropy are also observed in these films. The magnetization relaxation of the bilayers has a strong unidirectional contribution, which is in part caused by two-magnon scattering. However, a detailed analysis of in-plane angle and thickness dependent linewidth data strongly suggests the presence of a previously undescribed unidirectional relaxation mechanism.2

Perpendicularly magnetized CoFeB layers with ultra-thin non-magnetic insertion layers are very widely used as the electrodes in magnetic tunnel junctions for spin transfer magnetic random access memory devices. Exchange interactions play a critical role in determining the thermal stability of magnetic states in such devices and their spin torque switching efficiency.Here the exchange constant of free layers incorporated in full magnetic tunnel junction layer stacks, specifically CoFeB free layers with W insertion layers is determined by magnetization measurements in a broad temperature range. A significant finding is that the exchange constant decreases significantly and abruptly with W insertion layer thickness. The perpendicular magnetic anisotropy shows the opposite trend; it initially increases with W insertion layer thickness and shows a broad maximum for approximately one monolayer (0.3 nm) of W. These results highlight the interdependencies of magnetic characteristics required to optimize the performance of magnetic tunnel junction devices.