NSRRC Activity Report 2022

010 NSRRC ACTIVITY REPORT 2022 Fig. 2 : Conductivity of two non-volatile switchable AFM textures. (a) Image of the sample current mapping taken at a photon energy of ~719.5 eV, and the sample current across Z = 30 um and Z = −90 um, which are shown as the orange and green dashed lines, respectively. Geometric relationships of the ferroelectric polarization (P), AFM- axis, and sample current (I e ) for the (b) AFM cross domain and (c) AFM line domain. [Reproduced from Ref. 1] (a) (b) in Fig. 1(b) indicates a larger XMLD signal corresponding to the AFM line domain, and the blue region indicates a smaller XMLD signal corresponding to the AFM cross domain. Excitingly, this resulted in a “BFO” pattern as designed (shown in Fig. 1(b) ), which was composed of the two distinguishable AFM states. With this approach, one can write AFM domain patterns on strained BFO films in any shape. Given that the AFM domain size of BFO films can be trimmed down to the scale of tens of nanometers, the size of the written AFM domain pattern can be expected to be in the nanometer scale as well, offering tremendous potential for high-density memory integrations. To reset the AFM status, one can erase all written patterns by applying a magnetic field along the a axis once again. Importantly, it is possible to read the written AFM pattern electrically. In Fig. 2(a) , we present the same sample mapping image as in Fig. 1(b) , but now with the absorption sample current (I e ) taken at a photon energy of 719.5 eV, which is below the onset of the range of the Fe L 2 absorption resonance energy. In Fig. 2(a) , we also present the sample current across the orange and green dashed cross-section lines shown in the mapping image. Remarkably, a high contrast of approximately 30% in the absorption sample current between the inside and outside of the written “BFO” pattern was observed. The mechanism of the I e measurement is also schematically illustrated in Fig. 2(a) . Electrons are ejected by photons from the exposed surface into the vacuum and equilibrium occurs when the ejected electrons are replaced by electrons flowing in from the ground electrode, the LNO metallic layer, at the same rate. Thus, the measured I e is proportional to the time interval of electrons traveling from the ground to the sample surface. This traveling time depends on the electron drift velocity, which is inversely proportional to the conductivity. In other words, the difference in the absorption sample current I e can be treated as a difference in resistance. This indicates that the resistance of the AFM cross domain is lower than that of the AFM line domain by at least 30%. The possibilities of causing a resistance difference between two non-volatile AFM textures is related to the geometric relationship between the ferroelectric polarization and the AFM axis, as illustrated in Figs. 2(b) and 2(c) . For the AFM cross domain, the inherent ferroelectric polarization, the AFM-axis and the I e share the same plane, as shown in Fig. 2(b) . By contrast, such a sharing scheme, as shown in Fig. 2(a) , is broken for the AFM line domain, resulting in the change of the electron scattering events, thus causing a different resistance. Naturally, of future interest is quantitative modeling of the resistance difference of the two AFM textures that takes into account the relationship between the ferroelectric polarization and the AFM axis found in this work. Spintronics has revolutionized magnetic reading/writing technology and is expected to facilitate the development of next-generation semiconductor-based nanochips/ devices. Whether designed for sensing, memory, or logical applications, the active development of spintronics is closely related to antiferromagnetism. An antiferromagnet generates no stray field and thus offers great potential for high-density data storage. The dynamic behavior of spin in AFM, compared to ferromagnets, can be more responsive to stimuli, leading to a shorter switching interval between two antiferromagnetic states. These remarkable properties make AFM a promising candidate in the development of (c)