Electronic Transport Properties Of CoFeB Films And Its Heterostructures

Electronic transport properties of ferromagnetic materials and its heterostructures are important in spintronics.The spin polarization of CoFeB film is larger than traditional ferromagnetic metals?e.g.,Fe,Co?.The Curie temperature of CoFeB films is higher than room temperature.The investigation on electronic transport properties of CoFeB films and its heterostructures is significant to extend the application of CoFeB film in spintronic devices.CoFeB films and CoFeB/SiO₂/n-Si heterostructures are fabricated by facing-target magnetron sputtering.The surface morphology,microstructure,magnetic,electronic transport properties and scaling of anomalous Hall effect?AHE?in CoFeB films are investigated.The current-in-plane?CIP?and current-perpendicular-to-plane?CPP?electronic transport properties of CoFeB/SiO₂/n-Si heterostructures are analyzed systematically.The Hall effect in CoFeB/SiO₂/n-Si heterostructures is also investigated.The as-deposited CoFeB films are amorphous,which have smooth surface.Annealing at 400 oC can induce the crystallization of amorphous CoFeB film as the Co Fe?110?peak appears.CoFeB film is a soft ferromagnetic material with in-plane magnetic anisotropy.The magnetization of CoFeB film is insensitive to temperature.With the increase of film thickness,the magnetic hysteresis loop is characterized by “Transcritical Hysteresis Loop”.The Hall resistivity of amorphous CoFeB film increases with the increase of magnetic field up to 20 k Oe and gradually approaches saturation,which exhibits the character of AHE.The AHE resistivity increases with the decreased thickness.The crystallization can also lead to the decrease of AHE resistivity.The longitudinal resistivity,AHE resistivity and AHE conductivity of amorphous CoFeB film received quantum correction from electron localization at low temperatures.The scaling of AHE in amorphous CoFeB films shows two different behaviors at different temperature regions due to electron localization.The CIP electronic transport properties of CoFeB/SiO₂/n-Si heterostructures show a metal-to-insulator transition with the increased temperature.The character of Hall loops undergoes a crossover from AHE to ordinary Hall effect with the increasing magnetic field.The AHE resistivity first increases,and then decreases with the increase of temperature.A two current channels model has been proposed to understand such electronic transport properties.A backward diode-like rectifying behavior of CoFeB/SiO₂/n-Si heterostructure has been observed under CPP measurement model.The magnetoresistance?MR?of heterostructure can reach 2300% at 200 K,which is characterized by “Temperature Peak Type” with increasing temperature.The positive MR can be attributed to the magnetic field controlled impact ionization process of carriers.The diffusion voltage shifts to high voltage due to magnetic field.Such large positive MR effect extends a potential application of CoFeB films in spintronic diodes.