Highly efficient voltage control of spin and enhanced interfacial perpendicular magnetic anisotropy in iridium-doped Fe/MgO magnetic tunnel junctions

Abstract

Voltage control of spin enables both a zero standby power and ultralow active power consumption in spintronic devices, such as magnetoresistive random-access memory devices. A practical approach to achieve voltage control is the electrical modulation of the spin-orbit interaction at the interface between 3d-transition-ferromagnetic-metal and dielectric layers in a magnetic tunnel junction (MTJ). However, we need to initiate a new guideline for materials design to improve both the voltage-controlled magnetic anisotropy (VCMA) and perpendicular magnetic anisotropy (PMA). Here we report that atomic-scale doping of iridium in an ultrathin Fe layer is highly effective to improving these properties in Fe/MgO-based MTJs. A large interfacial PMA energy, K i,0 , of up to 3.7 mJ m − 2 was obtained, which was 1.8 times greater than that of the pure Fe/MgO interface. Moreover, iridium doping yielded a huge VCMA coefficient (up to 320 fJ Vm − 1 ) as well as high-speed response. First-principles calculations revealed that Ir atoms dispersed within the Fe layer play a considerable role in enhancing K i,0 and the VCMA coefficient. These results demonstrate the efficacy of heavy-metal doping in ferromagnetic layers as an advanced approach to develop high-density voltage-driven spintronic devices. NPG Asia Materials (2017) 9, e451; doi:10.1038/am.2017.204; published online 5 December 2017 INTRODUCTIONSpintronic devices, such as a magnetoresistive random-access memory device using a MgO-based magnetic tunnel junction (MTJ), 1,2 are expected to reduce the standby power of future computing systems by utilizing the non-volatile feature of magnetism. However, one significant challenge emerges from reducing the energy for information writing: magnetization switching. This issue is caused by electriccurrent-based operations of spintronic devices using electric-currentinduced magnetic fields, spin-transfer torque (STT) and spin-orbit torque based on the spin Hall effect rather than the electric-field-based operations presently used for semiconductor devices. For example, recent developments of STT-magnetoresistive random access memory have achieved~100 fJ per bit writing energies, 3 which corresponds to 10 7 k B T, where k B is the Boltzmann constant and T is the temperature (assumed to be 300 K here). In contrast, the energy required for maintaining magnetic information, that is, thermal stability, is between 60 k B T and 100 k B T. This large energy gap between data writing and retention, on the order of 10 5 , mainly originates

Impact of Spin-Transfer Torque on the Write-Error Rate of a Voltage-Torque-Based Magnetoresistive Random-Access Memory

“…Voltage-torque (VT) switching is another attractive method for low power writing, which is based on voltage control of magnetic anisotropy (VCMA) in a thin ferromagnetic film [4,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The mechanism of the VCMA in a MgO-based MTJ is considered as the combination of the selective electron/hole doping into the d-electron orbitals and the induction of a magnetic dipole moment, which affect the electron spin through the spin-orbit interaction [35][36][37][38][39].…”

Creation and Destruction of Skyrmions via Electrical Modulation of Local Magnetic Anisotropy in Magnetic Thin Films

“…in a thin film can be substantially modified by the external factors such as the film thickness and the strain with the substrate [30,42]. Similarly, the strength of the DMI (D) can be controlled through the choice of the spin-orbit coupled material as it is associated with the interaction at the interface [39].…”

“…outside the currently considered range (for instance, those adopted for PdFe/Ir(111) [45]). A recent experiment suggests that the anisotropy modulation in the range of 300-400 kJ/m 3 can be within reach via VCMA [30]. The magnetoelastic effect is expected to be effective as well [37].…”

“…In fact, the induced effective magnetic field was shown theoretically to enable efficient skyrmion transfer on the thin-film plane [23][24][25] as well as core reversal in a pillar geometry [26]. The effect of VCMA itself has been studied extensively in both ferromagnetic (FM) and antiferromagnetic (AFM) materials with a large change in the anisotropy field demonstrated in the literature [19,20,[27][28][29][30].…”

A Recent Progress of Spintronics Devices for Integrated Circuit Applications

“…For example, Noguchi et al reported VC-MRAM circuits for ultralarge last level cache memory, in which the voltage to switch the magnetization is as high as 2.2 V [10], which is larger than the standard CMOS power-supply voltage of less than 1.2 V. The necessity of such a large voltage originates from limited amounts of anisotropy modulation coefficients by E-field. To overcome this issue, the material development of the free-layer material is now underway [88][89][90][91][92]. Another issue to be addressed is the small time window for the writing.…”