Enhancing the interfacial perpendicular magnetic anisotropy and tunnel magnetoresistance by inserting an ultrathin LiF layer at an Fe/MgO interface

Abstract

Perpendicular magnetic anisotropy (PMA) is becoming increasingly important in spintronics research, especially for high-density magnetoresistive random access memories (MRAMs). The PMA induced at an Fe/MgO interface is widely used in magnetic tunnel junctions. Here, we propose inserting an ultrathin LiF layer at the interface in an epitaxial Fe/MgO junction. With a 0.3 nm-thick LiF layer, a large intrinsic interface PMA energy, Ki,0, of 2.8 mJ/m2 was achieved. We also found that the LiF/MgO bilayer tunneling barrier exhibited a large tunnel magnetoresistance (TMR) effect, suggesting that a coherent spin-dependent tunneling process was maintained in the ultrathin LiF layer. Atomic-scale interface engineering using fluoride can further improve the PMA and TMR properties of spintronic devices.

The origin of enhanced interfacial perpendicular magnetic anisotropy in LiF-inserted Fe/MgO interface

“…The coercive field increases with the LiF thickness up to 0.4 nm but decreases slightly when the LiF layer becomes 0.6-nm thick. This behavior is consistent with a previous study [27], suggesting that the PMA energy increases upon the LiF insertion. As the LiF thickness increases, peaks emerge and develop around 693, 701, and 715 eV, as indicated by dashed vertical lines in Fig.…”

“…The Fe/LiF/MgO heterostructures were grown on single-crystalline MgO(001) substrates by molecular beam epitaxy [27]. The sample structure (Fig.…”

“…Recently, Nozaki et al demonstrated that the insertion of an ultra-thin LiF layer between Fe and MgO remarkably enhances the interfacial PMA while maintaining or even increasing TMR [27]. Despite this promising discovery, the origin of the enhancement remains to be clarified, and such clarification is critical for further PMA improvement.…”

Ultralow Electric Current-Assisted Magnetization Switching due to Thermally Engineered Magnetic Anisotropy

“…Perpendicular magnetic anisotropy (PMA) materials are of great importance for spintronics because of their unique advantages including higher device density and much smaller switching current in STT- and SOT-based devices. − In application, compared with traditional PMA materials used in spintronics, the stubborn PMA of transition metal oxides (TMOs) without thickness limitation constitutes a major advantage. − The high adjustability of electronic and magnetic properties makes TMOs with PMA very attractive in both fundamental sciences and practical applications. , Metallic NiCo 2 O 4 (NCO) with strong PMA and high spin polarization is highly desirable for the development of low-power, high-speed spintronics including MRAMs and magnetic field sensors. − In addition, the magnitude of magnetoresistive based on NCO nanostructures can be further tuned by disorder and strain, which can be exploited for design of versatile devices with multifunctionality . Recently, the concept of thermally assisted MRAM has been experimentally verified by taking advantage of current pulses. ,,,− However, there are few reports on current controllable PMA of TMOs, which is a key element in building out-of-plane magnetic tunnel junctions for MRAM.…”

Interfacial Fe segregation and its influence on magnetic properties of CoFeB/MgFeO multilayers

“…[1][2][3][4] The CoFeB/MgO/CoFeB multilayer has been the most commonly used MTJ structure in MRAMs owing to a high TMR ratio and large interfacial PMA obtained from solidstate epitaxy of CoFe(B)/MgO(001). [4][5][6][7][8][9][10][11][12][13][14][15] The magnetic and electrical transport properties of CoFe(B)/MgO multilayers can be tailored by various approaches, such as changing the CoFe(B) alloy composition, 16,17) and/or inserting an ultrathin film of Mg, [18][19][20] Al, 21,22) or LiF 23) between the CoFe(B) and MgO layers. Another approach is to use Mg-X-O (X: transition metals) as a tunneling barrier.…”