To overcome a bottleneck in spintronic applications such as those of ultralow-power magnetoresistive random-access memory devices, the electric-field control of magnetization vectors in ferromagnetic electrodes has shown much promise. Here, we show the giant converse magnetoelectric (CME) effect in a multiferroic heterostructure consisting of the ferromagnetic Heusler alloy Co2FeSi and ferroelectric-oxide Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) for electric-field control of magnetization vectors. Using an in-plane uniaxial magnetic anisotropy of polycrystalline Co2FeSi film grown on PMN-PT(011), the nonvolatile and repeatable magnetization vector switchings in remanent states are demonstrated. The CME coupling coefficient of the polycrystalline Co2FeSi/PMN-PT(011) is over 1.0 × 10−5 s/m at room temperature, comparable to those of single-crystalline Fe1-xGax/PMN-PT systems. The giant CME effect has been demonstrated by the strain-induced variation in the magnetic anisotropy energy of Co2FeSi with an L21-ordered structure. This approach can lead to a new solution to the reduction in the write power in spintronic memory architectures at room temperature.

We study spin-polarized cation vacancies in wurtzite structure semiconductors (BeO, ZnO, ZnS, CdS, BN, AlN, GaN and GaP) by using first-principles calculations based on the density functional theory. We find that C3v geometries are the most stable and are spin-polarized. Two majority spin electrons occupying the defect E level lead to the magnetic moment of 2 μB in the case of II–VI semiconductors. On the contrary, in the case of III–V semiconductors, three majority spin electrons occupying the defect E and A1 levels induce the magnetic moment of 3 μB. The spin polarization of cation vacancies in oxides and nitrides are found to be stable compared with other cation vacancies in II–VI and III–V semiconductors, respectively. We clarify that the effect of the symmetry lowering from C3v to Cs is small and thus confirm that the spin polarized C3v geometries are the most stable.

We report the microscopic origin of strain-mediated changes in the magnetocrystalline anisotropy energy of the Co2FeSi, Co2MnSi, and Fe3Si Heusler alloys from the viewpoint of first-principles electron theory. Both Co2FeSi and Co2MnSi have similar anisotropy changes upon induced strain within the (001) plane, where the quadrupole moment due to Co minority-spin states dominates the anisotropy modulation, and, thus, giant magnetoelectric couplings in multiferroic heterointerfaces containing these compounds. In contrast, the strain-induced anisotropy modulation in Fe3Si has mixed contributing factors not limited to the anisotropy term of the orbital magnetic moment and the quadrupole term.