Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys

Abstract

This review discusses the recent studies of magnetization dynamics and the role of angular momentum in thin films of ferrimagnetic rare-earth-transition metal (RE-TM) alloys, e.g. GdFeCo, where both magnetization and angular momenta are temperature dependent. It has been experimentally demonstrated that the magnetization can be manipulated and even reversed by a single 40 fs laser pulse, without any applied magnetic field. This switching is found to follow a novel reversal pathway, that is shown however to depend crucially on the net angular momentum, reflecting the balance of the two opposite sublattices. In particular, optical excitation of ferrimagnetic GdFeCo on a time scale pertinent to the characteristic time of the exchange interaction between the RE and TM spins, i.e. on the time scale of tens of femtoseconds, pushes the spin dynamics into a yet unexplored regime, where the two exchange-coupled magnetic sublattices demonstrate substantially different dynamics. As a result, the reversal of spins appears to proceed via a novel transient state characterized by a ferromagnetic alignment of the Gd and Fe magnetic moments, despite their ground-state antiferromagnetic coupling.Thus, optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results. Considering the progress in the development of plasmonic antennas and compact ultrafast lasers, optical control of magnetic order may also potentially revolutionize data storage and information processing technologies.

Controlling the polarity of the transient ferromagneticlike state in ferrimagnets

“…Typical Gd concentrations used in recent experiments of ultrafast dynamics range from 10 to 30%. 4 Hence, these alloys behave as an "effective" ferromagnet, FeCo, defined mainly by the value of the intra-lattice exchange integral, J TT , and the Gd spins whose dynamics are mainly defined by the antiferromagnetic coupling to the FeCo spins, defined by the exchange integral J TR . The effect of Gd-Gd exchange interactions in these Gd concentrations (10 − 30%) is relatively small in comparison to other exchange interactions present in the system.…”

“…13,[37][38][39][40][41][42] In ferrimagnets, there is a large interest on demagnetization rates of each species, following the use of X-ray magnetic circular dichroism 5 to monitor the sub-picosecond dynamics of each sublattice magnetization individually. 4 Thermal effects dominate the magnetization dynamics during the heating produced by the laser. On this basis recent works 7,8 suggested that the typical demagnetization time of the sublattice ν is given by τ ν ∼ γ ν µ ν /(λ ν k B T e ), where T e refers to the dynamical electron temperature.…”

Ab InitioTheory of Coherent Laser-Induced Magnetization in Metals

“…Ls, 75.70.Tj, 75.60.Jk All-optical helicity-dependent magnetization switching has recently emerged as a promising way to manipulate and ultimately control the magnetization in a magnetic material using ultrashort optical laser pulses [1][2][3][4][5][6][7]. As femtosecond optical laser pulses are the shortest stimuli known to mankind, all-optical helicity-dependent switching offers novel options to achieve magnetization reversal at a hitherto unprecedented speed.…”

Helicity and field dependent magnetization dynamics of ferromagnetic Co/Pt multilayers

“…19 The laser-induced magnetization reversal observed in these ferromagnetic materials 3 does not fit the paradigm of the existing understanding of AOS in ferrimagnets. [20][21][22][23] The data reported in Ref. 3 only revealed the final states of the ferromagnetic samples after being excited by multiple laser pulses.…”