Ferromagnetism above Room Temperature in a Ni-Doped Organic-Based Magnetic Semiconductor

Abstract

Ferromagnetic semiconductors with structural flexibility are an indispensable feature for future flexible spin-electronic applications. In this case, we introduce magnetic ingredients into an organic semiconductor, namely, pentacene, to form a ferromagnetic organic semiconductor (FOS). The first observation for ferromagnetic Ni-doped pentacene semiconductors at room temperature in the field of semiconductor spintronics is reported in this article. To date, the mechanism of FOSs with ferromagnetism is not understood yet, especially when their Curie temperature is enhanced above room temperature. Here, we demonstrate dopants of Ni atoms and the modulation of the growth temperature in the FOS films to achieve room-temperature ferromagnetic properties in a series of FOS films, one of which has a maximum coercivity of 257.6 Oe. The spin-exchange interaction between a Ni atom and a pentacene molecule is detected through the magnetic hysteresis obtained using a superconducting quantum interference device magnetometer. We verify the effectiveness of this spin coupling through magnetic force microscopy, Raman spectroscopy, scanning Kelvin probe microscopy, and theoretical simulation. A model for the indirect spin coupling between Ni atoms is proposed for the mechanism of room-temperature ferromagnetic ordering of spins due to the exchange force indirectly. We believe that the π-electrons of pentacene molecules at the triple state for this model can support the spin coupling of electrons of Ni atoms. Our findings facilitate the development of brand-new spintronic devices with structural flexibility and room-temperature ferromagnetism.

Vibrationally Induced Magnetism in Supramolecular Aggregates

“…The results obtained within this article should be set in perspective with the recent observations of, e.g., increasing coercivity or enhanced chiral induced spin selectivity effect with temperature [23][24][25][29][30][31][32]. For instance, the molecular crystals investigated in Refs.…”

“…For instance, the molecular crystals investigated in Refs. [23][24][25]30 show an increasing coercive field up to 300 K, however, accompanied by decreasing remanent and saturated magnetizations. Such behavior is reproduced by the model for ferromagnetic spin exchange, see Fig.…”

“…The question to be addressed here is whether nuclear (ionic, molecular) vibrations can stabilize magnetic configurations or a magnetic order in structures in which the time-inversion symmetry is sustained in the absence of such vibrations. The investigation is stimulated by the experimental observations of room temperature ferromagnetism in self-assembled ensembles of paramagnetic and diamagnetic supramolecular aggre-gates or other types of molecular structures [23][24][25][27][28][29][30][31].…”

Vibrationally Induced Magnetism in Supramolecular Aggregates

“…The results obtained within this letter should be set in perspective with the recent observations of, e.g., increasing coercivity or the enhanced chiral-induced spin selectivity effect with the temperature. 23 − 25 , 29 − 32 For instance, the molecular crystals investigated in refs ( 23 − 25 and 30 ) show an increasing coercive field up to 300 K but accompanied by decreasing remanent and saturated magnetizations. Such behavior is reproduced by the model for ferromagnetic spin exchange (see Figure 6 b).…”

“…The question to be addressed here is whether nuclear (ionic and molecular) vibrations can stabilize magnetic configurations or a magnetic order in structures in which the time-reversal symmetry is sustained in the absence of such vibrations. The investigation is stimulated by the experimental observations of room-temperature ferromagnetism in self-assembled ensembles of paramagnetic and diamagnetic supramolecular aggregates or other types of molecular structures. − ,− …”