Ultrafast Double Pulse All-Optical Reswitching of a Ferrimagnet.

All-optical reswitching has been investigated in the half-metallic Heusler ferrimagnet Mn_{2}Ru_{0.9}Ga, where Mn atoms occupy two inequivalent sites in the XA-type structure. The effect of a second 200 fs, 800 nm laser pulse that follows the first pump pulse, when both are above the threshold for switching, is studied as a function of t_{12}, the time between them. Aims were to determine the minimum time needed for reswitching and to identify the physical mechanisms involved. The time trajectory of the switching process on a plot of sublattice angular momentum, S^{4a} vs S^{4c}, is in three stages; when t<0.1 ps, the sublattice moments are rapidly disordered, but not destroyed, while conserving net angular momentum via optical spin-wave excitations. This leads to transient parallel alignment of the residual Mn spins in the first quadrant. The net angular momentum associated with the majority sublattice then flips after about 2 ps, and a fully reversed ferrimagnetic state is then established via the spin-lattice interaction, which allows reswitching provided t_{12}>10 ps.

Sub-picosecond exchange-relaxation in the compensated ferrimagnet Mn2Ru x Ga.

We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn2Ru x Ga. While the two antiferromagnetically coupled sublattices are both composed of manganese, they exhibit different temperature dependencies due to their differing local environments. The sublattice magnetization dynamics triggered by femtosecond laser pulses are studied to reveal the roles played by the spin and intersublattice exchange. We find a two-step demagnetization process, similar to the well-established case of Gd(FeCo)3, where on a 5 ps timescale the two Mn-sublattices seem to have different demagnetization rates. The behaviour is analysed using a four-temperature model, assigning different temperatures to the two manganese spin baths. Even in this strongly exchange-coupled system, the two spin reservoirs have considerably different behaviour. The half-metallic nature and strong exchange coupling of Mn2Ru x Ga lead to spin angular momentum conservation at much shorter time scales than found for Gd(FeCo)3 which suggests that low-power, sub-picosecond switching of the net moment of Mn2Ru x Ga is possible.

Single pulse all-optical toggle switching of magnetization without gadolinium in the ferrimagnet Mn2RuxGa.

Energy-efficient control of magnetization without the help of a magnetic field is a key goal of spintronics. Purely heat-induced single-pulse all-optical toggle switching has been demonstrated, but so far only in Gd-based amorphous ferrimagnet films. In this work, we demonstrate toggle switching in films of the half-metallic ferrimagnetic Heusler alloys Mn2RuxGa, which have two crystallographically-inequivalent Mn sublattices. Moreover, we observe the switching at room temperature in samples that are immune to external magnetic fields in excess of 1 T, provided they exhibit a compensation point above room temperature. Observation of the effect in compensated ferrimagnets without Gd challenges our understanding of all-optical switching. The dynamic behavior indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis for fast optical switching of magnetization and break new ground for engineered materials that can be used for nonvolatile ultrafast switches using ultrashort pulses of light.