Large Tunnel Magnetoresistance of 1056% at Room Temperature in MgO Based Double Barrier Magnetic Tunnel Junction

Abstract

We retract the paper [Appl. Phys. Express 2 (2009) 083002] that reported on the large tunnel magnetoresistance (TMR) in double-barrier magnetic tunnel junctions (DBMTJs) with a thin middle layer because an incorrect measurement system was used. We used a voltage/current-source/monitor (Advantest R6243) and connected it to the sample, as shown in Fig. 1. If (i) the central DBMTJ is in a state of electrical breakdown, (ii) the pads A and B have large resistance, and (iii) the source and the sense are connected through a protection circuit in R6243, the TMR effect of the two pads drastically enhances the TMR ratio. We apologize for the fact that the large TMR ratio of DBMTJs reported in our paper was artificially generated owing to the incorrect four-probe measurement.The authors wish to express gratitude to N. Suzuki of ADC Corporation for fruitful discussion of R6243 measurement system.

Superparamagnetism in MgO-based magnetic tunnel junctions with a thin pinned ferromagnetic electrode

“…Inverted TMR ratios of −33% and −77% are obtained at 300 and 24 K for MTJs with t = 1.0 nm, which is less than the positive TMR value of up to 200% found for MTJs with a thicker pinned ferromagnetic layer. [7][8][9][10][11]15,16 The spin filter effect of the crystalline MgO barrier is much suppressed for these MTJs and the suppression should somehow be related to the thickness of the pinned CoFeB layer ͑see below͒. Degradation of the MgO layer may also contribute to the lowering of the TMR if the pinned CoFeB layer is not perfectly continuous.…”

“…[5][6][7][8][9][10][11] The basic MTJ structure is a sandwich with two ferromagnetic electrodes separated by a thin insulating barrier, which has applications in magnetic random access memory, read heads, and logic devices. In 2001, Butler et al 5 and Mathon and Umerski 6 predicted the large TMR effect in MTJs with single-crystal MgO barriers; very large TMR ratios of about 200% were subsequently reported in devices with ͑001͒-oriented MgO.…”

“…10 Pinned double barrier MTJs have been reported to show a record TMR ratio of 1056% at room temperature. 11 The positive TMR effect here is defined as ͑R AP − R P ͒ / R P , where R P and R AP are the resistances of the junctions when the moments of the ferromagnetic electrodes in contact with tunnel barrier are parallel and antiparallel, respectively. The high TMR in MgO-based MTJs devices is due to the filtering effect of the crystalline MgO barrier, which depends on symmetry of the ↑ and ↓ electron wave functions.…”

New directions in spintronics

“…By concentrating on improving the quality of the interface, the homogeneity of the barrier and the crystal orientation of the materials, TMR of 600 per cent has been realized. The promise of greater than 1000 per cent was thought to be fulfilled [25], albeit in a double-junction structure of CoFeB/MgO; however, in a sobering message to us all, the authors fell victim to an artefact of measurement electronics and have retracted [26] the original paper.…”

Structural and Material Exploration of Magnetic Tunnel Junctions

“…This is due in large part to the various potential technological applications utilizing the high TMR performance [18], which is quickly approaching the theoretically predicted value of over 1000% in Fe/MgO/Fe MTJ structure [20]. Recently, a TMR value of 605% was reported in a pseudo spin valve annealed at high temperature [58], and a record high TMR value of 1056% was reported in a double barrier MTJ structure with MgO as the barrier material [59]. However, the performance of MTJs is well known to be very sensitive to fabrication conditions, and significant challenges remain for fabrication of reliable high quality MTJs.…”