Conventional semiconductor devices use electric fields to control conductivity, a scalar quantity, for information processing. In magnetic materials, the direction of magnetization, a vector quantity, is of fundamental importance. In magnetic data storage, magnetization is manipulated with a current-generated magnetic field (Oersted-Ampère field), and spin current is being studied for use in non-volatile magnetic memories. To make control of magnetization fully compatible with semiconductor devices, it is highly desirable to control magnetization using electric fields. Conventionally, this is achieved by means of magnetostriction produced by mechanically generated strain through the use of piezoelectricity. Multiferroics have been widely studied in an alternative approach where ferroelectricity is combined with ferromagnetism. Magnetic-field control of electric polarization has been reported in these multiferroics using the magnetoelectric effect, but the inverse effect-direct electrical control of magnetization-has not so far been observed. Here we show that the manipulation of magnetization can be achieved solely by electric fields in a ferromagnetic semiconductor, (Ga,Mn)As. The magnetic anisotropy, which determines the magnetization direction, depends on the charge carrier (hole) concentration in (Ga,Mn)As. By applying an electric field using a metal-insulator-semiconductor structure, the hole concentration and, thereby, the magnetic anisotropy can be controlled, allowing manipulation of the magnetization direction.

The question whether the Anderson-Mott localisation enhances or reduces magnetic correlations is central to the physics of magnetic alloys 1 . Particularly intriguing is the case of (Ga,Mn)As and related magnetic semiconductors, for which diverging theoretical scenarios have been proposed 2-9 . Here, by direct magnetisation measurements we demonstrate how magnetism evolves when the density of carriers mediating the spin-spin coupling is diminished by the gate electric field in metal/insulator/semiconductor structures of (Ga,Mn)As. Our findings show that the channel depletion results in a monotonic decrease of the Curie temperature, with no evidence for the maximum expected within the impurity-band models 3,5,8,9 . We find that the transition from the ferromagnetic to the paramagnetic state proceeds via the emergence of a superparamagnetic-like spin arrangement. This implies that carrier localisation leads to a phase separation into ferromagnetic and nonmagnetic regions, which we attribute to critical fluctuations in the local density of states, specific to the Anderson-Mott quantum transition.Manipulation of magnetism by a gate electric field has been demonstrated in carrier-controlled ferromagnets by studies of the anomalous Hall effect 10-14 , resistance 15,16 and splitting of a luminescence line 17 .Such studies provide information on spin polarisation of itinerant carriers. In order to probe directly the effect of carrier localisation on magnetism we have developed superconducting quantum interference device (SQUID) magnetometery sensitive enough to determine quantitatively magnetisation of (Ga,Mn)As consisting the channel of metal-insulator-semiconductor (MIS) structures. A 3.5 thick film of Ga 0.93 Mn 0.07 As are grown at 220 o C on a 4 nm GaAs/30 nm Al 0.8 Ga 0.2 As/30 nm GaAs buffer layer structure on a semiinsulating GaAs(001) substrates by molecular beam epitaxy. For magnetic measurements, a series of (Ga,Mn)As-based large parallel-plate capacitors, with an average gate area A of about 10 mm 2 , with atomic layer deposition grown gate insulator HfO 2 of thickness d = 50 mm and the dielectric constant κ ≅ 20 has been prepared. The 3 nm Cr/50 nm Au gate electrode completes the structure. We regard a device as a prospective one if during room temperature current-voltage I-V characteristics tests within ±4 V (+/-~1MV/cm) the capacitor shows no indication of leaking (flat I-V 'curve' on 100 pA range indicating the

Spike-timing-dependent synaptic plasticity (STDP) is demonstrated in a synapse device based on a ferroelectric-gate field-effect transistor (FeFET). STDP is a key of the learning functions observed in human brains, where the synaptic weight changes only depending on the spike timing of the pre- and post-neurons. The FeFET is composed of the stacked oxide materials with ZnO/Pr(Zr,Ti)O3 (PZT)/SrRuO3. In the FeFET, the channel conductance can be altered depending on the density of electrons induced by the polarization of PZT film, which can be controlled by applying the gate voltage in a non-volatile manner. Applying a pulse gate voltage enables the multi-valued modulation of the conductance, which is expected to be caused by a change in PZT polarization. This variation depends on the height and the duration of the pulse gate voltage. Utilizing these characteristics, symmetric and asymmetric STDP learning functions are successfully implemented in the FeFET-based synapse device by applying the non-linear pulse gate voltage generated from a set of two pulses in a sampling circuit, in which the two pulses correspond to the spikes from the pre- and post-neurons. The three-terminal structure of the synapse device enables the concurrent learning, in which the weight update can be performed without canceling signal transmission among neurons, while the neural networks using the previously reported two-terminal synapse devices need to stop signal transmission for learning.