Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO

We use femtosecond electron diffraction to study ultrafast lattice dynamics in the highly correlated antiferromagnetic (AFM) semiconductor NiO. Using the scattering vector (Q) dependence of Bragg diffraction, we introduce Q-resolved effective temperatures describing the transient lattice. We identify a nonthermal lattice state with preferential displacement of O compared to Ni ions, which occurs within ∼0.3  ps and persists for 25 ps. We associate this with transient changes to the AFM exchange striction-induced lattice distortion, supported by the observation of a transient Q asymmetry of Friedel pairs. Our observation highlights the role of spin-lattice coupling in routes towards ultrafast control of spin order

Robust Magnetic Order Upon Ultrafast Excitation of an Antiferromagnet

The ultrafast manipulation of magnetic order due to optical excitation is governed by the intricate flow of energy and momentum between the electron, lattice, and spin subsystems. While various models are commonly employed to describe these dynamics, a prominent example being the microscopic three temperature model M3TM , systematic, quantitative comparisons to both the dynamics of energy flow and magnetic order are scarce. Here, an M3TM was applied to the ultrafast magnetic order dynamics of the layered antiferromagnet GdRh2Si2. The femtosecond dynamics of electronic temperature, surface ferromagnetic order, and bulk antiferromagnetic order were explored at various pump fluences employing time and angle resolved photoemission spectroscopy and time resolved resonant magnetic soft X ray diffraction, respectively. After optical excitation, both the surface ferromagnetic order and the bulk antiferromagnetic order dynamics exhibit two step demagnetization behaviors with two similar timescales lt;1 ps, amp; 8764;10 ps , indicating a strong exchange coupling between localized 4f and itinerant conduction electrons. Despite a good qualitative agreement, the M3TM predicts larger demagnetization than the experimental observation, which can be phenomenologically described by a transient, fluence dependent increased N el temperature. The results indicate that effects beyond a mean field description have to be considered for a quantitative description of ultrafast magnetic order dynamic

Deterministic control of an antiferromagnetic spin arrangement using ultrafast optical excitation

A central prospect of antiferromagnetic spintronics is to exploit magnetic properties that are unavailable with ferromagnets. However, this poses the challenge of accessing such properties for readout and control. To this end, light-induced manipulation of the transient ground state, e.g. by changing the magnetic anisotropy potential, opens promising pathways towards ultrafast deterministic control of antiferromagnetism. Here, we use this approach to trigger a coherent rotation of the entire long-range antiferromagnetic spin arrangement about a crystalline axis in GdRh2Si2 and demonstrate deterministic control of this rotation upon ultrafast optical excitation. Our observations can be explained by a displacive excitation of the Gd spins' local anisotropy potential by the optical excitation, allowing for a full description of this transient magnetic anisotropy potential

Element specific magnetization redistribution at YBa2Cu3O7 La2 3Ca1 3MnO3 interfaces

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Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO

We use femtosecond electron diffraction to study ultrafast lattice dynamics in the highly correlated antiferromagnetic (AFM) semiconductor NiO. Using the scattering vector (Q) dependence of Bragg diffraction, we introduce Q-resolved effective temperatures describing the transient lattice. We identify a nonthermal lattice state with preferential displacement of O compared to Ni ions, which occurs within ∼0.3  ps and persists for 25 ps. We associate this with transient changes to the AFM exchange striction-induced lattice distortion, supported by the observation of a transient Q asymmetry of Friedel pairs. Our observation highlights the role of spin-lattice coupling in routes towards ultrafast control of spin order

Ultrafast probe of magnetization dynamics in multiferroic CoCr2O4 and Co0.975Ge0.025Cr2O4

We report on element resolved ultrafast magnetization dynamics in multiferroic CoCr2O4 and Co0.975Ge0.025Cr2O4 after optical excitation above the electronic band gap. We observe demagnetization dynamics in the range of several picoseconds, up to two orders of magnitude faster than previously reported demagnetization in other ferrimagnetic insulators. Moreover, we find that the dynamics of the two magnetic ions differ significantly just below the Curie point. The dynamics of the low temperature multiferroic phase are almost two times slower than those in the ferrimagnetic phase. This suggests that the additional magnetic cycloidal component, which is coupled to electric polarization at low temperatures, might influence the ultrafast magnetization dynamic