Application of coherent light–matter interactions has recently been extended to the ultrafast control of magnetization. An important but unrealized technique is the manipulation of magnetization vector motion to make it follow an arbitrarily designed multidimensional trajectory. Here we demonstrate a full manipulation of two-dimensional magnetic oscillations in antiferromagnetic NiO with a pair of polarization-twisted femtosecond laser pulses. We employ Raman-type nonlinear optical processes, wherein magnetic oscillations are impulsively induced with a controlled initial phase. Their azimuthal angle follows well-defined selection rules that have been determined by the symmetries of the materials. We emphasize that the temporal variation of the laser-pulse polarization angle enables us to control the phase and amplitude of the two degenerate modes, independently. These results lead to a new concept of the vectorial control of magnetization by light.

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We have studied growth condition dependence of magnetic and transport properties of magnetic semiconductor (GaMn)As grown by low-temperature molecular-beam epitaxy (LT-MBE). With increasing substrate temperature and decreasing As overpressure during the growth of (Ga1−xMnx)As with x=0.043, the hole concentration increased, the conduction behavior changed from semiconducting to metallic, and the ferromagnetic transition temperature became higher. This is explained by a decrease in the compensation of Mn acceptors by the reduction of excess As related defects in the LT-MBE grown (GaMn)As. Our experimental results indicate that the selection of the MBE growth parameters is very important for better controlling the electronic and magnetic properties of (GaMn)As.

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