Photonic integrated circuits require magneto-optical (MO) materials for making nonreciprocal devices such as isolators and circulators. The most successful MO materials are rare-earth-substituted iron garnets, but these can be challenging to grow on silicon without a seed layer, which introduces spacing loss between the waveguide and the MO cladding. A pulsed-laser deposition (PLD) method is used for making MO Ce:YIG (Ce 1 Y 2 Fe 5 O 12 )/YIG (Y 3 Fe 5 O 12 ) bilayer or trilayer films on different substrates, including silicon, quartz, and Gd 3 Ga 5 O 12 (GGG), in which a multilayer film is deposited in one run and then annealed. A YIG seed layer grown above the MO Ce:YIG facilitates recrystallization during ex situ rapid thermal annealing, which results in a reduced thermal budget and simplified deposition process. A monolithically integrated optical isolator was demonstrated by direct deposition of a bilayer Ce:YIG/YIG capping layer onto a siliconon-insulator resonator. The device exhibited an insertion loss of 7.4 ± 1.8 dB and an isolation ratio of 13.0 ± 2.2 dB within the telecommunication window (λ = 1564.4 nm), which outperforms previously reported monolithic isolators.

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Self-assembled BiFeO3-CoFe2O4 nanocomposites were templated into ordered structures in which the ferrimagnetic CoFe2O4 pillars form square arrays of periods 60-100 nm in a ferroelectric BiFeO3 matrix. The ferroelectricity, magnetism, conductivity, and magnetoelectric coupling of the ordered nanocomposites were characterized by scanning probe microscopy. The insulating BiFeO3 matrix exhibited ferroelectric domains, whereas the resistive CoFe2O4 pillars exhibited single-domain magnetic contrast with high anisotropy due to the magnetoelasticity of the spinel phase. Magnetoelectric coupling was observed in which an applied voltage led to reversal of the magnetic pillars.

There is great interest in self-assembled oxide vertical nanocomposite fi lms consisting of epitaxial spinel pillars in a single crystal perovskite matrix, due to their tunable electronic, magnetic, and multiferroic properties. Varying the composition or geometry of the pillars in the out-of-plane direction has not been previously reported but can provide new routes to tailoring their properties in three dimensions. In this work, ferrimagnetic epitaxial CoFe 2 O 4 , MgFe 2 O 4 , or NiFe 2 O 4 spinel nanopillars with an out-of-plane modulation in their composition and shape are grown in a BiFeO 3 matrix on a (001) SrTiO 3 substrate using pulsed laser deposition. Changing the pillar composition during growth produces a homogeneous pillar composition due to cation interdiffusion, but this can be suppressed using a suffi ciently thick blocking layer of BiFeO 3 to produce bi-pillar fi lms containing for example a layer of magnetically hard CoFe 2 O 4 pillars and a layer of magnetically soft MgFe 2 O 4 pillars, which form in different locations. A thinner blocking layer enables contact between the top of the CoFe 2 O 4 and the bottom of the MgFe 2 O 4 which leads to correlated growth of the MgFe 2 O 4 pillars directly above the CoFe 2 O 4 pillars and provides a path for interdiffusion. The magnetic hysteresis of the nanocomposites is related to the pillar structure.