Photoinduced Melting of Antiferromagnetic Order inLa0.5Sr1.5MnO4Measured Using Ultrafast Resonant Soft X-Ray Diffraction

Abstract

We used ultrafast resonant soft x-ray diffraction to probe the picosecond dynamics of spin and orbital order in La(0.5)Sr(1.5)MnO(4) after photoexcitation with a femtosecond pulse of 1.5 eV radiation. Complete melting of antiferromagnetic spin order is evidenced by the disappearance of a (1/4,1/4,1/2) diffraction peak. On the other hand, the (1/4,1/4,0) diffraction peak, reflecting orbital order, is only partially reduced. We interpret the results as evidence of destabilization in the short-range exchange pattern with no significant relaxation of the long-range Jahn-Teller distortions. Cluster calculations are used to analyze different possible magnetically ordered states in the long-lived metastable phase. Nonthermal coupling between light and magnetism emerges as a primary aspect of photoinduced phase transitions in manganites.

The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures

“…The long-lived phase that emerges from the photoexcitation process could be spindisordered or ferromagnetic or a mixture of the two. The results of cluster calculations indicated that both are possible in the presence of unperturbed Jahn-Teller distortions [91].…”

“…The work at Diamond was extended to higher temporal resolution by operating the synchrotron in a low-α mode which allowed the dynamics to be studied with a resolution of approximately 10 ps [91]. However, to understand the details of photomelting antiferromagnetic order on the femtosecond time scale requires the temporal resolution available only at an X-ray free electron laser (XFEL).…”

“…The interest in these materials arises due to the small energy difference between different phases that develop upon doping so that pressure, magnetic fields and light can be used to reversibly switch from one phase to another. The group of Cavalleri (Oxford and Centre for Free-Electron Lasers, Hamburg) along with Dhesi (Diamond Light Source) developed time-resolved soft X-ray diffraction on the Nanoscience beamline (I06) to study the single-layered manganite La 0.5 Sr 1.5 MnO 4 [91,92]. This material undergoes a metal-insulator transition at approximately 240 K resulting in charge and orbital ordering in the MnO 2 planes.…”

“…RSXD was used on the Nanoscience beamline (I06) to study the ultrafast spin and orbital dynamics in La 0.5 Sr 1.5 MnO 4 . The intensities of the ( 1 4 , 1 4 , 1 2 ) and ( 1 4 , 1 4 ,0) diffraction peaks, related to spin-ordering and orbital ordering, respectively, were studied following excitation with an 800 nm laser pulse [91]. By following the dynamics of the ( 1 4 , 1 4 , 1 2 ) and ( 1 4 , 1 4 ,0) diffraction peaks in the time domain, it was possible to separate the evolution of both the magnetic and orbital degrees of freedom following photoexcitation.…”

Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3

“…6 On the other hand, photoirradiation may induce non-thermal metastable states or transient phases with optical, magnetic and electric properties distinct from that of the ground states. [7][8][9] Among these light-responsive materials, the ferromagnetic materials have been brought into sharp focus by laser-induced demagnetization since Bigot and coworkers found the ultrafast dropping of magnetization in nickel film following optical pulses in 1996. 6 Until recently, the ultrashort pulses of light are applied to manipulate the ultrafast processes in the antiferromagnets.…”