Magnetic coupling at interface of ultrathin Co film and antiferromagnetic Cr₂O₃ (0001) film

The magnetic coupling at the interface of Co and Cr has been investigated using ultrathin Co film on Cr₂O₃ (0001) film, which is expected to be a promising system to show the magnetoelectronic effect. We mainly examined the temperature dependence of magnetization, the exchange bias at different field directions relative to the Cr spin direction, and the temperature dependence of exchange bias. The temperature dependence of magnetization under 50 Oe indicates the collinear coupling of Co spin and Cr spin at the interface. Furthermore, the exchange bias effect is observed in the coupled direction of Co and Cr, namely, parallel to the Cr spin direction. However, the changes in the magnetic behavior with changing field directions and Co thicknesses imply the existence of biquadratic coupling of Co spin and Cr spin, as well. In agreement with the numerical calculation under the coexistence of collinear and biquadratic couplings, the exchange bias field decreases nonmonotonically with increasing temperature.Yu Shiratsuchia, Toshihiro Nakatani, Shin-ichi Kawahara, and Ryoichi Nakatani, Journal of Applied Physics 106, 033903 (2009); https://doi.org/10.1063/1.3182802

Interploidy gene flow involving the sexual-asexual cycle facilitates the diversification of gynogenetic triploid Carassius fish

クローン繁殖フナは稀に有性生殖をしながら繁栄 --遺伝的に多様なクローンフナが存在する謎を解明--. 京都大学プレスリリース. 2021-11-19.Asexual vertebrates are rare and at risk of extinction due to their restricted adaptability through the loss of genetic recombination. We explore the mechanisms behind the generation and maintenance of genetic diversity in triploid asexual (gynogenetic) Carassius auratus fish, which is widespread in East Asian fresh waters and exhibits one of the most extensive distribution among asexual vertebrates despite its dependence on host sperm. Our analyses of genetic composition using dozens of genetic markers and genome-wide transcriptome sequencing uncover admixed genetic composition of Japanese asexual triploid Carassius consisting of both the diverged Japanese and Eurasian alleles, suggesting the involvement of Eurasian lineages in its origin. However, coexisting sexual diploid relatives and asexual triploids in Japan show regional genetic similarity in both mitochondrial and nuclear markers. These results are attributed to a unique unidirectional gene flow from diploids to sympatric triploids, with the involvement of occasional sexual reproduction. Additionally, the asexual triploid shows a weaker population structure than the sexual diploid, and multiple triploid lineages coexist in most Japanese rivers. The generated diversity via repeated interploidy gene flow as well as an increased establishment of immigrants is assumed to offset the cost of asexual reproduction and might contribute to the successful broad distribution of this asexual vertebrate