Abstract
Excitation of antiferromagnetic HoFeO3 with a single 80 fs laser pulse triggers a first-order spin-reorientation phase transition. In the ultrafast kinetics of the transition one can distinguish the processes of impulsive excitation of spin precession, nucleation of the new domain and growth of the nuclei. The orientation of the spins in the nuclei is defined by the phase of the laser-induced coherent spin precession. The growth of the nuclei is further promoted by heating induced by the laser excitation. Hereby we demonstrate that in HoFeO3 coherent control of the spin precession allows an effective control of the route of the heat-induced first-order magnetic phase transition. The theoretical description of the excitation of the spin precession by linearly-polarized ultrashort laser pulses is developed with the sigma model. The analysis showed high sensitivity of the excited dynamics to the initial spin orientations with respect to the crystallographic axes of the material.
Highlights
Ultrafast magnetism, starting from the seminal observation of subpicosecond demagnetization of Ni films [1], has developed into a rapidly growing scientific area in the last two decades with a potential to impact modern digital technology
We show that the magnetization dynamics in HoFeO3 can be launched via the inertial mechanism by means of linearly polarized light in phases which are characterized by non-zero x and y components of L
We have shown that an ultrashort laser pulse can trigger spin reorientation in HoFeO3 over 90 degrees
Summary
Ultrafast magnetism, starting from the seminal observation of subpicosecond demagnetization of Ni films [1], has developed into a rapidly growing scientific area in the last two decades with a potential to impact modern digital technology. We demonstrate that ultrafast time-resolved imaging of the photo-induced magnetization reveals stages of nucleation and consequent growth of the nuclei These stages are typical for the kinetics of first-order phase transitions. We unambiguously demonstrate that while the magnetization growth is an incoherent process driven by the laser heating of the lattice, the sign of the magnetization in the growing nuclei is predefined by the phase of the coherent spin precession impulsively excited by the femtosecond laser pulse This allowed us to conclude that the initial coherent oscillations are stimulus for the following orientation phase transition which determine the spin orientation in the final magn etic phase. A further increase of the temperature pulls the antiferromagnetic vector in the (0 1 0) plane towards the x-axis This rotation is accomplished at T3 = 58 K when the spins are oriented along the xaxis and the net magnetic moment is pointing solely along the z-direction.
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