High-frequency susceptibility of a weak ferromagnet with magnetostrictive magnetoelectric coupling: Using heterostructures to tailor electromagnon frequencies

In the first part of this work we calculate the high-frequency magnetoelectric susceptibility of a simultaneously ferroelectric and canted antiferromagnetic (also known as weak ferromagnetic) thin film with magnetostrictive magnetoelectric coupling. We show that a dynamic coupling exists between the ferroelectric and optic antiferromagnetic excitations. In the second part of the paper, we calculate, using an effective medium method, the susceptibility of a heterostructure comprising alternating thin films of such a material together with a ferromagnet. Dipolar magnetic fields serve to couple the ferromagnetic and optic antiferromagnetic modes, which in turn couples the ferromagnetic and ferroelectric excitations. This provides a mechanism for creating “electromagnon” modes in the microwave regime which may be useful for applications

Spin wave valve in an exchange spring bilayer

Spin wave resonances are calculated for two exchange coupled ferromagnetic films with different magnetic anisotropies. In this structure a domain wall can be pinned near the interface and affect spin wave frequencies. We find that the exchange spring can decrease the decay length of excitations at the interface by enhancing the frequency mismatch between the two films. We also propose the function of such a structure as a spin wave “valve.” Dipolar contributions to the spin wave energies are estimated using a method adapted from an effective medium approximation in the magnetostatic limit

Parametric spin wave excitation and cascaded processes during switching in thin films

A theory for calculating the threshold precession angles required to parametrically excite spin waves during large-angle switching of in-plane magnetized films is presented. Analytic expressions for the parametric thresholds are found for finite thickness films when due to three- and four-wave decays. Precession at the threshold angle will produce appreciable spin wave amplitudes only after infinite time. We show that much larger angles are required to experimentally observe nonlinearities within a finite time. This may explain apparent discrepancies reported between ultrafast pulsed reversal and longer time scale high-power ferromagnetic resonance experiments. A comparison of our results to published experimental data for metallic Permalloy films is made. Finally, the film thickness dependence of the threshold is examined and a minimum is found corresponding to when a particular “cascaded” spin wave interaction is resonant

Resonant frequencies of a binary magnetic nanowire

10.1103/PhysRevB.87.064424Physical Review B - Condensed Matter and Materials Physics876-PRBM

Structure and magnetism of ultra small cobalt particles assembled at titania surfaces by ion beam synthesis

Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra small, oxidation resistant, cobalt nanoparticles embedded within substoichiometric TiO2 amp; 948; thin films. Using high fluence implantation of cobalt at 20 60 keV, the particles were assembled with an average size of 1.5 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near edge X ray fluorescence spectroscopy on the L2,3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and superparamagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element resolved X ray magnetic circular dichroism, and depth resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reaction

The energy bands of quantized spin waves and the uniaxial anisotropy in a biferromagnetic system

The eigenproblems of quantized spin waves in a (100) ferromagnetic bilayer system have been investigated theoretically using the interface rescaling approach. The energy-band structure of the system has been obtained and the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands are explored thoroughly. It is found that all kinds of eigenmodes of the spin waves in the biferromagnetic system are determined by the bulk exchange coupling constant, the interface exchange coupling constant, the spin of lattice, the number of atomic layers and the uniaxial bulk anisotropy. Especially, we explore the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands of first Brillouin zone and the existence condition of all kinds of the eigenmodes