Fabrication of magnetic tunnel junctions with a single-crystalline LiF tunnel barrier

Abstract

We fabricated Fe/LiF/Fe magnetic tunnel junctions (MTJs) by molecular beam epitaxy on a MgO(001) substrate, where LiF is an insulating tunnel barrier with the same crystal structure as MgO (rock-salt type). Crystallographical studies such as transmission electron microscopy and nanobeam electron diffraction observations revealed that the LiF tunnel barrier is single-crystalline and has a LiF(001)[100] k bottom Fe(001) [110] crystal orientation, which is constructed in the same manner as MgO(001) on Fe(001). Also, the in-plane lattice mismatch between the LiF tunnel barrier and the Fe bottom electrode was estimated to be small (about 0.5%). Despite such advantages for the tunnel barrier of the MTJ, the observed tunnel magnetoresistance (MR) ratio was low (>6% at 20 K) and showed a significant decrease with increasing temperature (>1% at room temperature). The results imply that indirect tunneling and/or thermally excited carriers in the LiF tunnel barrier, in which the current basically is not spin-polarized, play a major role in electrical transport in the MTJ.

Theoretical study of rectifying properties in a terahertz regime with a zero-bias voltage for fully epitaxial Fe/ZnO/MgO/Fe magnetic tunnel junctions

“…Magnetic tunnel junctions (MTJs), which basically consist of MIM or MIIM structures, have been widely used as a core component for practical device applications, such as the read heads of hard disk drives. [23][24][25][26][27][28][29][30][31][32] Very recently, we fabricated epitaxial Fe(001)/ZnO(001)/MgO(001)/Fe(001) MTJs with a MIIM structure, in which the ZnO has a metastable rocksalt crystal structure. 33) For this MTJ system, highly asymmentic J-V characteristics were observed at room temperature (RT), in addition to a tunneling magnetoresistance effect.…”

Structural and magneto-transport properties of lattice-mismatched epitaxial Fe/SrO/MgO/Fe magnetic tunnel junctions

“…the unit cell of the MgO was turned 45°with regard to the Fe bottom electrode. 4,9,11,12) For the SrO tunnel barrier, we observed elongated spotty patterns having a four-fold symmetry [Fig. 2(c , respectively.…”

“…Epitaxial tunnel barrier is the core component of magnetic tunnel junctions (MTJs) showing giant tunneling magnetoresistance (MR) effect at room temperature (RT) based on the phenomenon called coherent spin-polarized tunneling. [1][2][3][4][5][6][7][8][9][10][11][12] As examples of the epitaxial tunnel barrier, MgO, [1][2][3][4] MgAl 2 O 4 , 5,6) GaAl 2 O 4 , 7) ZnO, [8][9][10] and GaO x 11,12) have been reported so far. These insulators are of rock salt-or spinel-type crystal structures having small lattice mismatches (Δa/a) with conventional 3d-ferromagnetic (FM) of bcc-Fe (Co).…”

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

“…Moreover, a previous theoretical study predicted that the Fe/LiF/Fe trilayer should exhibit a large TMR of 2400% [24], although reported experimental TMR ratios were no more than 20 % at room temperature because of the poor crystallinity of LiF [25,26].…”