Fast neutron tolerance of the perpendicular-anisotropy CoFeB–MgO magnetic tunnel junctions with junction diameters between 46 and 64 nm

Abstract

This work represents the first-ever investigation of the effects of fast neutron exposure on the perpendicular-anisotropy CoFeB–MgO magnetic tunnel junctions (p-MTJs) with practical junction diameters (D) between 46 and 64 nm. In this study, 461 p-MTJs, each with a tunnel magnetoresistance (TMR) ratio above 90%, were irradiated with fast neutrons at a total 1 MeV equivalent fluence of 3.79 × 1012 cm−2, corresponding to 1.90 × 1011 h irradiation with fast atmospheric neutrons (20 cm−2 h−1), without applying a bias voltage. Following irradiation, there were no changes in the properties of these devices, such as their resistance versus magnetic field curves, resistance values in the parallel and anti-parallel states, or TMR ratios, regardless of the neutron fluence. On the basis of these data, the nuclear reactions that occur under the specific experimental neutron irradiation conditions employed in this work are discussed.

Ar+ ion irradiation of magnetic tunnel junction multilayers: impact on the magnetic and electrical properties

“…A scheme of the multilayer stack and the coordinate system are shown in the inset of figure 1. Both FL and RL possess an effective first-order anisotropy field, B K1eff = 2ks1 tMS − µ 0 M S , encompassing the competition between the interfacial perpendicular magnetic anisotropy (k s1 /t), originated at the FeCoB/MgO interfaces, and the thin-film shape anisotropy 1 2 µ 0 M 2 S . The PL is exchange-biased to the antiferromagnetic IrMn (J EB > 0) and coupled antiferromagnetically via a RKKY-like interlayer exchange coupling across the Ru spacer to the RL (J IEC < 0), constituting a typical synthetic antiferromagnet (SAF) structure.…”

“…dynamic RAM) is its superior radiation hardness with respect to gamma rays and charged particles in the MeV range. That hardness makes MRAM promising for applications in extreme environments [1]. Still, magnetic tunnel junctions (MTJs) are not tolerant to all sorts of radiation [2][3][4]: indeed, ion-irradiation-induced modifications of MTJs have been observed, extending from soft errors (undesired but recoverable magnetization switching, provoked by localized heating [4]) to permanent changes in magnetic and electrical properties produced by structural modifications.…”

“…as: (1) saturation of the magnetization of the three layers along the field direction; (2) parallel configuration of the MTJ, obtained after the switching of PL M ;(3) antiparallel configuration of the MTJ, following the switching of FL M ; and (4) saturation in the direction opposite to(1). Using the values of each plateau (see SM2 in the Supplemental Material) the magnetization values were estimated as The numbers in parentheses identify the different magnetization configurations in the MTJ, also depicted in the figure.…”

“…= , for a magnetic field applied in plane, opposite to the exchange-bias field H  . Blue squares are experimental results, and the red line is a fit to the experiment following equation(1).The interlayer exchange coupling field, 0 IEC μH , is the field required to compensate the coupling when going from configuration (3) to configuration (4) in figure1. IEC J is thus determined as: PL M is accompanied by…”

Shaping Perpendicular Magnetic Anisotropy of Co2MnGa Heusler Alloy Using Ion Irradiation for Magnetic Sensor Applications

“…Various strategies have been explored to tailor the anisotropy of Heusler alloys, such as strain-induced anisotropy change [60], buffer layer effects [61,62], doping-induced disorder effects [63] and irradiation [8,[64][65][66]. Modification of the magnetic properties of various materials via irradiation has been reported for several types of irradiations, such as plasma of various gasses [67,68], ionizing radiation [69,70], high-energy protons and cosmic rays, X-rays [71], neutrons [72] and even several low and swift heavy ion irradiations [73,74]. Among these techniques, ion irradiation is a well-established technique for shaping the magnetic properties of materials due to its high precision and control over the irradiation parameters, such as the ion species, ion energy and ion beam current density [8,[64][65][66]75,76].…”