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VIDEO DOI: https://doi.org/10.48448/r2cw-z035

technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Ferromagnetic hysteresis loop induced by electric field effect on Pt/CoFe2O4

Pt has been considered as a system close to ferromagnetic state because Pt has a large density of states near the Fermi energy. Magnetic moment in Pt ultrathin film was reported to be induced by a magnetic proximity effect through a spinel ferrimagnet CoFe2O4(CFO) at room temperature, and a saturation value of the anomalous Hall effect (AHE), which is proportional to magnetic moment, was tuned by an electric field effect (1). In this report, we induced a ferromagnetic hysteresis in ultrathin Pt (5.9 nm) by electric field-effect at low temperature. Both the remanence and the coercive field were tuned from zero to a finite value. A ferrimagnetic insulator CFO thin film (~ 50 nm) with TC above 300 K were prepared on a SrTiO3(STO) substrate by a pulse laser deposition. With a hall-bar shaped photoresist mask a 5.9 nm Pt film was fabricated by sputtering (Pt/CFO sample). Another Pt (5.9 nm) film was also prepared on a STO substrate as a sample for comparison (Pt/STO sample). Electric double layer transistors (EDLT) were fabricated on these samples using an ionic liquid electrolyte (DEME-TFSI) and a Pt gate electrode. Figures show a magnetic field dependence of an anomalous Hall resistivity ρAH at 2 K for the Pt/CFO (Fig. 1) and Pt/STO (Fig. 2) samples, respectively. An ordinary Hall coefficient RH was estimated at 250 K for samples before the fabrication of the EDLT, and ρAH was estimated by ρAH = ρxy-RHB. For a gate bias (VG) of 0 V, both samples showed no hysteresis loop, while AHE was observed. By applying VG = -3 V and +3 V, the Pt/CFO sample showed clear hysteresis loop, indicating ferromagnetism induced by the VG . On the other hand, no such behavior was observed in Pt/STO. These results suggest that the ferromagnetism of Pt is induced both by the MPE from the adjacent CFO layer and tuning of Fermi level by gating. The remanence for VG = +3 V decreased with increasing temperature, and disappeared at around 19.5 K, probably corresponding to the TC of Pt. In the presentation, we will discuss the origin of the AHE.

(1) S. Nodo, S. Ono, and Y. Toshihiro, Appl. Phys. Exp., Vol. 13, p.063004 (2020)


Transcript English (automatic)

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