Suchergebnisse

Partially disordered FePt nanoparticles prepared by the sputtering method and protected by Al2 O3 constitute an interesting realization of graded media, recently suggested for future generations of magnetic recording. By depositing the alumina layer, the particle is partially disordered with gradually varying properties. The current work comprises a comparison between experimental data and atomistic modeling results of the coercive field and energy barriers in FePt particles with gradually spatially varying properties, specifically the magnetization, anisotropy, and exchange constants. From our modeling we conclude that the magnetization reversal processes for dynamic reversal at the coercive field and for the zero field energy barrier involve different reversal modes. The coercive field decreases as a function of disordering length up to 2 T and is in good agreement with measured values. The zero field energy barrier, except for highly disordered particles, is almost independent of the disordering length, retaining the high values required for thermal stability. ; G.R.A. wants to thank her postdoctoral grants conceded by the Basque Government and the CSIC JAE fellowship. The SGI/IZO-SGIker UPV/EHU is gratefully acknowledged for allocation of computational resources. This work has also been supported by the Spanish Ministry of Science and Education Project No. NAN-2004-09125-C07-06 and by the project NANOMAGNET from Comunidad de Madrid.

Materials that possess nontrivial topology and magnetism is known to exhibit exotic quantum phenomena such as the quantum anomalous Hall effect. Here, we fabricate a novel magnetic topological heterostructure Mn4Bi2Te7/Bi2Te3 where multiple magnetic layers are inserted into the topmost quintuple layer of the original topological insulator Bi2Te3. A massive Dirac cone (DC) with a gap of 40–75 meV at 16 K is observed. By tracing the temperature evolution, this gap is shown to gradually decrease with increasing temperature and a blunt transition from a massive to a massless DC occurs around 200–250 K. Structural analysis shows that the samples also contain MnBi2Te4/Bi2Te3. Magnetic measurements show that there are two distinct Mn components in the system that corresponds to the two heterostructures; MnBi2Te4/Bi2Te3 is paramagnetic at 6 K while Mn4Bi2Te7/Bi2Te3 is ferromagnetic with a negative hysteresis (critical temperature ~20 K). This novel heterostructure is potentially important for future device applications. ; T.H. was supported by JSPS KAKENHI Grant Number 18H03877, the Murata Science Foundation (No. H30-084), the Asahi Glass Foundation, Tokyo Tech. Challenging Research Award, and the Iketani Science and Technology Foundation (No. 0321083-A). M.K. was supported by the Spintronics Research Network of Japan (Spin-RNJ). The ARPES measurements were performed under the UVSOR proposal Nos. 29-837, 30-571, 30-860 and the SARPES measurements were performed under the HiSOR proposal No. 16BG001. The XMCD measurements were performed at JAEA beamline BL-23SU in SPring-8 (Proposal No. 2018B3843) and also at PF-KEK (PF PAC No. 17P006). The work at SPring-8 was performed under the Shared Use Program of JAEA Facilities (Proposal No. 2018B-E21) with the approval of Nanotechnology Platform project supported by the Ministry of Education, Culture, Sports, Science and Technology (Proposal No. A-18-AE-0039). The support by Tomsk State University competitiveness improvement program (No. 8.1.01.2018), the Saint Petersburg State University (Project ID 51126254), the Russian Science Foundation (Grant No. 18-12-00169) and the Government research assignment for ISPMS SB RAS, project No. III.23.2.9 is gratefully acknowledged. M.M.O. acknowledges the support by Spanish Ministerio de Ciencia e Innovación (Grant No. PID2019-103910GB-I00). ; Peer reviewed