Spin wave spectra and spatially modulated structures in BiFeO3

Abstract

The spin wave spectra of antiferromagnetic BiFeO3-type multiferronics are analyzed theoretically. The presence of a spatially modulated cycloidal antiferromagnetic structure leads to a countable number of frequency branches of two oscillatory modes (Goldstone and activation) for spin waves propagating along a cycloid. When there is no magnetic field and anisotropy, the magnon spectrum is characterized by the absence of frequency gaps. The spectral features of the spin oscillations with changing anisotropy and application of a magnetic field are identified and the limits on the existence of an antiferromagnetic cycloid are established up to its transformation into a conical structure. In the transverse direction the spin oscillations have a mixed character which indicates that the cycloid is stable with respect to bending throughout its domain of existence.

Excitation of spin waves in BiFeO3multiferroic film by the slot line transducer

“…With a large film thickness, it is difficult to provide the conditions for the absence of a spatially modulated antiferromagnetic structure. In the latter case, a multi-frequency spectrum of spin waves [3][4][5] arises due to the presence of an antiferromagnetic cycloid and the conversion efficiency will depend substantially on the orientation and location of the spatial modulation of the spins relative to the antenna slot line.…”

“…In low magnetic fields, the ground state of BFO is characterized by the presence of a cycloidal spatially modulated antiferromagnetic structure [25], with a discrete set of frequencies in the spin wave spectrum [4,5,20]. When analyzing the spectrum of spin waves in a cycloid, we consider the case where its spatial modulation is going along the direction [ 1 1 0].…”

“…The presence of spontaneous electric polarization and antiferromagnetic ordering makes this multiferroic promising for applications in spintronics and magnonics [1]. Owing to antiferromagnetic ordering, the observed spin-wave spectrum of this multiferroic lies in the range of extremely high frequencies (EHF) [2][3][4][5]. The electric field in a multiferroic BFO type can control the transition from a spatially modulated phase to a homogeneous state, accompanied by a crucial rearrangement of the spin-wave spectrum [6].…”