The loss of mechanical stability and the critical magnetization of a ferromagnetic particle in an elastomer.

The rotation of a spherical magnetically soft ferromagnetic particle with uniaxial magnetic anisotropy and located in an elastomer through a certain angle under the action of a magnetic field has been studied theoretically. It was found that if the particle loses its mechanical stability, its rotation angle becomes critically dependent on the magnetic field magnitude. The magnetically induced critical rotation of the particle in the elastomer has a magneto-elastic origin and is accompanied by a critical change in the magnetization of the particle multidomain state, as occurs in the case of second-order magnetic phase transitions. The transition of a particle in a soft-elastic elastomer from the multidomain state into a uniformly magnetized one was shown to be independent of the magnitude of the particle magnetic anisotropy field. The particle rotation was found to result in the appearance of a maximum in the field dependence of the magnetic susceptibility.

Spin dynamics in a Curie-switch.

Ferromagnetic resonance properties of F1/f/F2/AF multilayers, where weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic layers F1 and F2, with F1 being magnetically soft and F2-magnetically hard due to exchange pinning to antiferromagnetic layer AF, are investigated. Spacer-mediated exchange coupling is shown to strongly affect the resonance fields of both F1 and F2 layers. Our theoretical calculations as well as measurements show that the key magnetic parameters of the spacer, which govern the ferromagnetic resonance in F1/f/F2/AF, are the magnetic exchange length (Λ), effective saturation magnetization at T = 0 (m0) and effective Curie temperature (T(C)(eff)). The values of these key parameters are deduced from the experimental data for multilayers with f = Ni(x)Cu(100-x), for the key ranges in the Ni-concentration (x = 54 ÷ 70 at. %) and spacer thickness (d = 3 ÷ 6 nm). The results obtained provide a deeper insight into thermally-controlled spin precession and switching in magnetic nanostructures, with potential applications in spin-based oscillators and memory devices.

Resonant activation of a synthetic antiferromagnet.

The magnetic decay time of a synthetic antiferromagnet comprised of two closely spaced magnetic dipoles is measured in the presence of microwave excitation. The system is known to be highly stable with respect to switching between its two antiparallel ground states under quasistatic magnetic fields. We show that an order of magnitude lower field can switch the pair, provided the field is applied in resonance with the optical eigenmode of the collective spin dynamics in the system. We furthermore show that thermal agitation can play an essential role in spin-flop switching for resonant excitations of near- or subcritical amplitude.

Interference of coexisting para- and ferromagnetic phases in partially crystallized films of doped manganites.

Electron spin resonance spectra have been studied in partially crystallized films of La(1-x)Na(x)MnO(3) (x = 0.16) in the vicinity of the para- to ferromagnetic transition. The objects of investigation were obtained by magnetron sputtering on polycrystalline Al(2)O(3) substrates held at different temperatures. It is shown that, in a regime where the paramagnetic and ferromagnetic phases coexist, the resonance conditions for one phase strongly depend on the parameters of the other phase. As a result, the resonance field of the paramagnetic phase becomes dependent on the shape of the sample, the saturation magnetization and the fraction of the ferromagnetic phase. A simple model is developed to predict the character of the changes in the resonance field of the paramagnetic phase upon the nucleation of the ferromagnetic phase.

A remarkable transformation of magnetic resonance spectra as a result of a mutual influence of coexisting para- and ferromagnetic phases.

In this work, we carry out the analysis of the resonance absorption of electromagnetic radiation for the system in which para- and ferromagnetic phases coexist over a wide temperature region. It is found that taking account of the mutual influence of coexisting phases gives rise to the appearance of substantial changes in the curves of resonance absorption and values of resonance fields, as well as to making the geometry of a phase distribution dependent on an external magnetic field. Near the temperature boundaries of the phase coexistence region, the expressions for description of the curves of the dispersive absorption of electromagnetic radiation are obtained and the rules of the behaviour of the resonance fields for each of the phases are specified. As follows from the calculations, the resonance field for the paramagnetic phase becomes dependent on the shape of the sample, the saturation magnetization and the fraction of ferromagnetic phase. It is shown that the character of magnetic resonance spectra and the features of their temperature change agree well with the experimental data, obtained by various groups of researchers on the single crystalline and polycrystalline samples of doped perovskite manganites.