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 .

The chalcogenide spinel CdCr 2 S 4 is a well-established ferromagnetic semiconductor that exhibits unique properties and is a promising candidate for spintronic applications. With band gap in the visible wavelength region, CdCr 2 S 4 nanocrystals offer the exciting possibility of tailoring both the optical and magnetic properties with precise morphology control. However, the synthesis of monodisperse CdCr 2 S 4 nanocrystals is challenging and has not been reported. A unique "seed-mediated" growth process has been developed for the synthesis that involves using cubic-phase CdS, which has a face-centered cubic crystal structure similar to that of CdCr 2 S 4 , as a "seed" to react with CrCl 3 •6H 2 O in a solution mixture of 1-dodecanethiol and 1-octadecene. Remarkably, hexagonal-phase CdS is ineffective as a "seed" for formation of the desired product. A mechanism for formation of monodisperse CdCr 2 S 4 nanocrystals by the selective growth process is proposed, and the structural and magnetic properties of the synthesized nanocrystals are presented. The novel synthetic strategy can be exploited for the controlled formation of other complex magnetic chalcogenides.

We investigate magnon spin transport in epitaxial nickel ferrite (NiFe 2 O 4 , NFO) films grown on magnesium gallate spinel (MgGa 2 O 4 , MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%, resulting in the reduction of antiphase boundary defects and thus in improved magnetic properties in the NFO films. In the nonlocal transport experiments, enhanced signals are observed for both electrically and thermally excited magnons, and the magnon relaxation length (λ m ) of NFO is found to be around 2.5 µm at room temperature. Moreover, at both room and low temperatures, we present distinct features from the nonlocal spin Seebeck signals which arise from magnonpolaron formation. Our results demonstrate excellent magnon transport properties (magnon spin conductivity, λ m and spin mixing conductance at the interface between Pt) of NFO films grown on a lattice-matched substrate that are comparable with those of yttrium iron garnet.

The effect of B-site cation ordering on the room temperature structural and ferromagnetic resonance (FMR) properties of single crystal spinel lithium ferrite (LiFe5O8, LFO) have been investigated. A detailed microstructural analysis is done through X-ray diffraction, polarized Raman spectroscopy, and transmission electron microscopy (TEM) to examine the effect of post-annealing on the B-site cation ordering. The X-ray diffraction pattern of the as-grown crystal indicates a disordered state of the crystal. However, the annealed sample shows additional superlattice reflections corresponding to the ordered phase. This ordering is further confirmed by Raman spectra and TEM images, which reveal ordering of Li and Fe ions at the octahedral sites contrasting with the relatively high degree of octahedral site disorder in the as-grown crystal. To study the effect of B-site ordering on the magnetic properties and FMR linewidth, vibrating sample magnetometry and broadband FMR measurements have been performed for both the ordered and disordered phases of lithium ferrite. The value of saturation magnetization for both phases is ∼290 emu/cm3. A single mode FMR profile is observed for both phases with little distortion. The linewidth characteristics of the ordered and disordered phases of lithium ferrite phases are compared, and it is observed that the linewidth is independent of the cation ordering. Both the phases exhibit a low linewidth (∼26 Oe at 30 GHz) and the effective damping parameter for the as-grown and annealed samples is determined to be 0.0021 ± 0.0001.

Magnetic 1/f noise is compared in magnetic tunnel junctions with electron-beam evaporated and sputtered MgO tunnel barriers in the annealing temperature range 350 -425 C. The variation of the magnetic noise parameter (a mag ) of the reference layer with annealing temperature mainly reflects the variation of the pinning effect of the exchange-bias layer. A reduction in a mag with bias is associated with the bias dependence of the tunneling magnetoresistance. The related magnetic losses are parameterized by a phase lag e, which is nearly independent of bias especially below 100 mV. The similar changes in magnetic noise with annealing temperature and barrier thickness for two types of MgO magnetic tunnel junctions indicate that the barrier layer quality does not affect the magnetic losses in the reference layer. V C 2012 American Institute of Physics.

The nature of mechanical strain-mediated converse magnetoelectric effect (CME) has been studied in multiferroic composites of single-crystal like thin films of nickel ferrite (NFO) and polycrystalline lead zirconate titanate (PZT). Ferrite films of thickness 0.45 to 1 micron were prepared by Pulsed Laser Deposition on lattice-matched (100) and (110) substrates of magnesium gallate (MGO) and cobalt gallate (CGO) that resulted in elimination of antiphase boundaries and magnetic parameters comparable to bulk single crystals. Ferromagnetic resonance under a static electric field E was utilized for studies of CME effects in composites of PZT and NFO films on the substrates. The in-plane static magnetic field H was applied along the principal crystallographic axes of the ferrite film to study its influence on CME.The E-induced ME anisotropy field HME was estimated from FMR data based on shift in resonance frequency with E in order to determine the ME constant A = HME/E. In composites with NFO films on (110) substrates (i) the ME coupling was stronger for films on CGO possibly due to a better lattice match and weaker substrate clamping than for films on MGO, (ii) A-values were the highest for H // [1,-1,0], and (iii) a negative A-value was inferred for H //[001]. For composites with NFO on (100) substrates the strongest ME coupling was measured for H along [001]. A first model for CME that takes into consideration both compressive and bending deformation in the composites is developed and results of the theory are in agreement with both the sign and magnitude of the measured ME coefficient A.The results of the studies presented here indicate the potential for use of the composites in self-biased E-tunable microwave devices.

We utilize spin Hall magnetoresistance (SMR) measurements to experimentally investigate the pure spin current transport and magnetic properties of nickel ferrite (NiFe 2 O 4 ,NFO)/normal metal (NM) thin film heterostructures. We use (001)-oriented NFO thin films grown on lattice-matched magnesium gallate substrates by pulsed laser deposition, which significantly improves the magnetic and structural properties of the ferrimagnetic insulator. The NM in our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude for charge currents applied in the [100]-and [110]direction of NFO yields a change of 50% for Pt at room temperature. We also investigated the temperature dependence of this current direction anisotropy and find that it is qualitatively different for the conductivity and the SMR magnitude. From our results we conclude that the observed current direction anisotropy may originate from an anisotropy of the spin mixing conductance or of the spin Hall effect in these Pt and Ta layers, and/or additional spin-galvanic contributions from the NFO/NM interface.The advent of (spin) angular momentum transport without an accompanying charge current, i.e. the flow of pure spin currents, has led to the discovery of several remarkable effects that are relevant for next generation spin electronic devices 1-3 . Amongst these effects is the spin Hall magnetoresistance 3-9 in magnetically ordered insulator (MOI)/ normal metal (NM) heterostructures, which enables the detection of novel magnetic phases in MOIs 10-12 . While initial investigations of the SMR heavily relied on yttrium iron garnet (YIG), the report on the observation of the SMR in many other MOIs ranging from ferrimagnetic 5,13,14 to antiferromagnetic [15][16][17][18][19] order confirms the universality of this effect. The magnitude of the SMR effect crucially depends on the transparency of the MOI/NM interface as well as the spin Hall effect (SHE) and the spin diffusion length of the NM. Nevertheless, the impact of the current direction with respect to the crystalline orientations on the SMR remains up to now unexplored. In this publication we experimentally show that the SMR amplitude in nickel ferrite thin films with bulk-like magnetic properties 20 interfaced with Ta or Pt depends upon the relative orientation of the charge current j compared to the NFO crystal axes.The heterostructures investigated in this study are NFO/NM bilayers, where the NM is Pt and Ta. The ferrimagnetic NFO thin films (≈ 100 nm) are grown on (001)-oriented MgGa 2 O 4 (MgGO) substrates via pulsed laser deposition. The bulk MgGO single crystals were obtained by the Czochralski method at the Leibniz-Institut für Kristallzüchtung, Berlin, Germany 21 , and substrates were then prepared by CrysTec GmbH, Berlin, Germany. During growth the substrate was kept at 700 • C in an oxygen atmosphere with 10 mTorr. For a) Electronic mail: matthias.althammer@wmi.badw.de the magnetotransport experiments we then defined NM Hall bar structures on top of the NFO with a width of 80 µm and a...

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