Growth-induced Uniaxial Magnetic Anisotropy Research Articles

Stress-tailoring magnetic anisotropy of V2O3/Ni bilayers

We report on a temperature-driven reversible change of the in-plane magnetic anisotropy of ${\mathrm{V}}_{2}{\mathrm{O}}_{3}/\mathrm{Ni}$ bilayers. This is caused by the rhombohedral to monoclinic structural phase transition of ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ at ${T}_{C}=160$ K. The in-plane magnetic anisotropy is uniaxial above ${T}_{C}$, but as the bilayer is cooled through the structural phase transition, a secondary magnetic easy axis emerges. Ferromagnetic resonance measurements show that this change in magnetic anisotropy is reversible with temperature. We identify two structural properties of the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}/\mathrm{Ni}$ bilayers affecting the in-plane magnetic anisotropy: (1) a growth-induced uniaxial magnetic anisotropy associated with steplike terraces in the bilayer microstructure and (2) a low-temperature strain-induced biaxial anisotropy associated with the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural phase transition. Magnetoresistance measurements corroborate the change in magnetic anisotropy across the structural transition and suggest that the negative magnetostriction of Ni leads to the emergence of a strain-induced easy axis. This shows that a temperature-dependent structural transition in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ may be used to tune the magnetic anisotropy in an adjacent ferromagnetic thin film.

Electric control of magnetic properties in epitaxially grown FeRh/MgO/PMN-PT heterostructures

We epitaxially grew the metamagnetic FeRh films on ferroelectric PMN-PT(001) substrates and investigated the electric control of magnetic properties. An MgO buffer layer is inserted to reduce the considerably large lattice mismatch of 5.44% between FeRh and PMN-PT, leading to a nice epitaxial growth with a relationship of FeRh[110](001)||MgO[100](001)||PMN-PT[100](001). The as-grown FeRh film shows a typical antiferromagnetic-to-ferromagnetic phase transition by means of varying the temperature. Because a growth-induced uniaxial magnetic anisotropy is superimposed on the in-plane four-fold magnetocrystalline anisotropy, the epitaxial FeRh film displays different kinds of multi-step hysteresis loops at various field orientations. An electric field applied on the PMN-PT substrate can remarkably increase the coercivity of FeRh film, which presents a butterfly type shape, indicating a strain-mediated magnetoelectric coupling. Because of the inhibitory effect of the remnant compressive strain on the phase transition, the critical transition temperature and the magnetization are obviously enhanced and reduced, respectively, after removing the electric effect.

Ferromagnetic Resonance Study of Fe/Cu Multilayer Thin Film

Fe/Cu/Fe multilayer thin film was grown on Si (100) substrate by using magnetron sputtering technique at room temperature. Dynamic and static magnetisations of the film have been investigated using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques in the temperature range of 10–300 K. From the room-temperature in-plane FMR measurements, a growth-induced uniaxial magnetic anisotropy was observed. Out-of-plane FMR measurements exhibited a large magnetic anisotropy due to a large saturation magnetisation of Fe. A computer code was written to simulate the experimental FMR data and to obtain the magnetic parameters of the Fe/Cu/Fe multilayer thin film. g value, effective magnetisation, uniaxial anisotropy field and perpendicular anisotropy constant from the fitting of the angular dependence of the resonance field at both the in-plane and out-of plane geometries were determined. The exchange bias effect was observed from the low-temperature VSM measurements. The saturation magnetisation and coercive field decrease with increasing temperature due to the increase of the thermal fluctuations.

Temperature-dependent exchange bias properties of polycrystalline PtxCo1 − x/CoO bilayers

Temperature and Pt concentration dependence of exchange bias in PtxCo1−x/CoO bilayers are investigated. It is observed that exchange bias properties, blocking temperature and magnetic anisotropy of the PtxCo1−x/CoO thin films are strongly affected by the concentration of Pt at the common interface. A detailed structural analysis of antiferromagnetic CoO has been done by x-ray photoelectron spectroscopy (XPS). The XPS data revealed that CoO layer grows with non-stoichiometric behavior which results in other cobalt oxide phases and thus lowers blocking temperature for the exchange biased systems. Increase of Pt concentration in PtCo layer strengthens the exchange bias and thus decreases training of the system. It also results in enhancement of growth-induced uniaxial magnetic anisotropy and onset of exchange bias at higher temperatures. The role of Pt concentration on the interfacial interactions between ferromagnetic and antiferromagnetic layers, and the effect of superstoichiometric CoO on blocking temperature are also discussed.

Surface morphology and magnetic anisotropy of Fe/MgO(001) films deposited at oblique incidence

We studied surface morphology and magnetic properties of Fe/MgO(001) films deposited at an angle varying between 0° and 60° with respect to the surface normal and with azimuth along the Fe[010] or the Fe[110] direction. Due to shadowing, elongated grains appear on the film surface for deposition at sufficiently large angle. X-ray reflectivity reveals that, depending on the azimuthal direction, films become either rougher or smoother for oblique deposition. For deposition along Fe[010] the pronounced uniaxial magnetic anisotropy (UMA) results in the occurrence of “reversed” two-step and of three-step hysteresis loops. For deposition along Fe[110] the growth-induced UMA is much weaker, causing a small rotation of the easy axes.

Uniaxial magnetic anisotropy in cobalt films induced by oblique deposition of an ultrathin cobalt underlayer

The in-plane magnetization of a series of 30 Å polycrystalline cobalt films on Si(111) substrates was investigated as a function of deposition angle. The films exhibited a growth-induced uniaxial magnetic anisotropy with an easy axis of magnetization that is initially perpendicular to the adatom flux direction but rotates to parallel to the deposition direction for an oblique incidence of 75°. The coercivity increased steadily for incidence angles above 30° from a value of 15 to 270 Oe at 75° depositions. A new technique to induce the uniaxial anisotropy onto a cobalt film deposited at normal incidence with the use of a cobalt underlayer deposited at oblique incidence was demonstrated. An underlayer film of 6 Å cobalt deposited at 83° induced an observed coercivity of 375 Oe in a 30 Å cobalt film.

Growth-induced uniaxial magnetic anisotropy in Co/Cu(100)

Growth-induced uniaxial magnetic anisotropy of Co/Cu(100) films were investigated using surface magneto-optic Kerr effect and scanning tunneling microscopy (STM). We found that the Co films off-grown at 230 K show an in-plane uniaxial magnetic anisotropy with the easy magnetization axis perpendicular to the growth incident plane. STM measurements show that the low temperature grown Co film consists of smaller islands without obvious anisotropic roughness or elongated islands. This result implies that the dipolar interaction does not dominate the uniaxial magnetic anisotropy. The CO absorption experiment further suggests that the uniaxial magnetic anisotropy originates from the magnetocrystalline step anisotropy of the Co film surface.

Growth-induced magnetic and optic anisotropy in bismuth-substituted iron garnet films

The growth-induced uniaxial magnetic anisotropy constant Kgu and the growth-induced birefringence Δng of (111) oriented epitaxial iron garnet films of composition R3−xBixFe5−yAlyO12 with R=Y, Gd, Sm have been investigated as a function of supercooling temperature ΔTs. The uniaxial anisotropy constant Kgu increases linearly with increasing ΔTs (0≤ΔTs≤100 K) in agreement with results reported for other bismuth-substituted rare-earth iron garnets. Δng turns out to be a linear function of Kgu and ΔTs. Δng is independent of the rare-earth species R in contrast to Kgu. The optical anisotropy arises primarily from the iron ions on the octahedral and tetrahedral sites as could be shown by the strong influence of diamagnetic dilution of the iron sublattices in the garnet crystal.

GROWTH-INDUCED BIREFRINGENCE IN LPE-GROWN IRON GARNET FILMS

The optical birefringence of various LPE-grown rare-earth and Bi-substituted iron garnet films are studied. In addition to the stress-induced birefringence, it is shown that there exists growth-induced birefringence ΔnfG in the films containing light rare-earth or Bi ions. In Bi garnet films the ΔnfG disappears on annealing and the thermal behavior of ΔnfG is similar to that of the growth-induced uniaxial magnetic anisotropy constant KuG. Furthermore, the BiG content dependence of ΔnfG is similar to that of KuG. As a result, it is suggested that the ΔnfG and KuG originate in the same microscopic structure which is of an anisotropic character. It is pointed out that the positive sign and the magnitude of ΔnfG in Bi garnet films are effective for the phase matching between TE and TM modes in a planar waveguide.

Guided-wave properties and mode conversions in (BiNdLu)<inf>3</inf>(FeAlLu)<inf>5</inf>O<inf>12</inf>films

The guided-wave properties and TE-TM mode conversions for LPE-grown (BiNdLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeAlLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> films were studied. A complete (100%) TE-TM mode conversion efficiency was attained by controlling the stress- and growth-induced optical birefringences which seriously influence the phase matching between the TE and TM modes. The mode conversion saturated under an external magnetic field at less than 8 Oe parallel to the light propagation direction. The correlation between growth-induced birefringence and growth-induced uniaxial magnetic anisotropy is discussed. It was found that the magnetooptical figure of merit |θ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> |/α reached more than 160 deg/dB at wavelength λ=1.15μm. These results show that (BiNdLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeAlLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> films are promising materials for waveguide-type magneto-optical application.

Optical and magneto-optical characteristics at 1.54&amp;#181;m of Co, Ge doped YNdIG LPE garnet films

Contribution of the Co ion to the growth-induced uniaxial magnetic anisotropy (Kug) has been observed in Co,Ge substituted yttrium-neodymium-iron garnet films grown on GGG substrates by the LPE method. Kug of the films on

Lead substitution in yttrium iron garnet

Polycrystalline and single crystal thin films of lead substituted Y 3Fe 5O 12 (Pb-YIG) have been prepared. The lattice parameter (a o) has been measured as a function of composition and the relationship Δ a o = 0.040 x A ̊ and 0.060x Å for polycrystalline and epitaxially grown films, respectively has been deduced (x is the number of lead atoms per formula unit). From the behaviour of polycrystalline Pb-YIG upon annealing we conclude that the thin films have a non-equilibrium composition. The hyperfine fields at the 57Fe nuclei measured by the Mössbauer effect are essentially the same as those of YIG. The Mössbauer spectra of the epitaxially grown films demonstrate that a growth-induced uniaxial magnetic anisotropy is present.