Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling

Abstract

Understanding quantitatively the heating dynamics in magnetic tunnel junctions (MTJ) submitted to current pulses is very important in the context of spin-transfer-torque magnetic random access memory development. Here we provide a method to probe the heating of MTJ using the RKKY coupling of a synthetic ferrimagnetic storage layer as a thermal sensor. The temperature increase versus applied bias voltage is measured thanks to the decrease of the spin-flop field with temperature. This method allows distinguishing spin transfer torque (STT) effects from the influence of temperature on the switching field. The heating dynamics is then studied in real-time by probing the conductance variation due to spin-flop rotation during heating. This approach provides a new method for measuring fast heating in spintronic devices, particularly magnetic random access memory (MRAM) using thermally assisted or spin transfer torque writing.Index Terms -Spin transfer torque, Interlayer Exchange Coupling, Temperature measurement, heating dynamics.In MRAM, a current is sent through a magnetic tunnel junction (MTJ) to switch the storage layer magnetization by spin transfer torque (STT) [1][2][3], or in the plane of the bottom electrode if the storage layer magnetization is switched by spin orbit torque (SOT) [4][5][6]. In all cases, the readout is performed by measuring at low bias voltage (~0.2V) the resistance of the MTJ which differs in parallel and antiparallel magnetic configuration due to the tunnel magnetoresistance phenomenon (TMR). Depending on the current amplitude, pulse duration and MTJ resistance, the current can also increase the temperature because of the power dissipated in the line or in the junction [7][8][9]. Solutions to reduce the current flow and the associated power consumption are currently under investigation, in particular by using the voltage control of magnetic anisotropy [10]. The switching behavior of spin torque driven devices [11][12][13][14] is greatly influenced by a temperature increase, possibly larger than 100°C even during pulses in the nanosecond range. The temperature variations affect the magnetic parameters, such as magnetization, magnetocrystalline anisotropy, and change the thermal activation energy. If the relationship between MTJ temperature and current intensity is unknown, an additional free parameter must be adjusted to fit the experimental switching phase diagrams and derive the spin torque efficiency. This unknown T(V) relationship cannot be addressed by simply comparing the coercivity dependence with temperature to that created by Joule heating because in most cases the current necessary for heating is large enough to induce spin-torque that impacts the coercivity of the device, as later detailed in this paper. Therefore, it is important to know the relation between temperature and voltage by other means. As an example, this has been recently investigated using the spin-wave thermal population as a temperature probe [15].In Thermally Assisted MRAM (TA-MRAM) [7][8][9], the storage layer ...

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“…In line with previous studies [66,67], we define the offset field H offset = H P-AP sw + H AP-P sw + ∆H ∆T /2 and the coercive field H c = H P-AP sw − H AP-P sw + ∆H ∆T /2 in terms of the sum and difference of H sw for different switching polarities, as illustrated in Fig. 3(a).…”

Impact of Joule heating on the stability phase diagrams of perpendicular magnetic tunnel junctions

“…To estimate the temperature variation and its voltage dependence in MTJs, we performed an experiment by the method described in Ref. [24] based on the temperature dependence of RKKY coupling, using the sample similar to that from On the V-H diagrams in FIG. 1 one can note some asymmetry between the critical lines for positive and negative voltage polarities.…”

LAS-NCS: A Laser-Assisted Spintronic Neuromorphic Computing System

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