Temperature dependence of magnetoresistance in magnetic tunnel junctions with different free layer structures

Abstract

The temperature and bias voltage dependence of magnetoresistance and the resistance of two types of magnetic tunnel junction ͑MTJ͒ samples were studied. These two types of MTJ samples have different free layer structures, while having the same pinned layer structures and with the same material for free and reference layers. The layer structure for type 1 MTJs is 80Ru-8CoFeB-15Al 2 O 3 -50CoFeB-9Ru-54FeCo-350CrMnPt ͑in angstroms͒. The layer structure for type 2 MTJs is 80Ru-40CoFeB-50RuTa-40CoFeB-15Al 2 O 3 -50CoFeB-9Ru-54FeCo-350CrMnPt. The tunneling magnetoresistance ͑TMR͒ ratio ͓͑R AP -R P ͒ / R P ͔ is about 26% and 69% at room temperature for type 1 and type 2 MTJs, respectively. A TMR as high as 107% has been observed for type 2 MTJ samples at 13 K. By analysis of the voltage and temperature dependence of the resistance and magnetoresistance in these MTJs, we discuss the effects of the magnetic behavior of the free layers, barrier qualities, and barrier interfaces. The results clearly indicate that the micromagnetization orientation at the interface between the free layer and the barrier layer is one of the important factors that determines the TMR ratio.

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

“…The fitting values of P 0 and ␣ are 56% and 4 ϫ 10 −5 , which agrees well with the fitting results in Ref. 19. The inelastic tunneling appears in these MgObased MTJ devices due to the CoFeB particles at the bottom CoFeB/MgO interface.…”

“…For an MTJ, the temperature dependence of the junction resistance is usually explained in terms of elastic and inelastic tunneling. 14,19 In this picture, the temperature dependence of the averaged conductance in the antiparallel and parallel states of MTJs is given by the following equations:…”

“…͑3͒. 19 However, because the pinned CoFeB layer has a small moment for these MgO-based MTJs, the elastic tunneling from this layer is weak, which may have a small influence on the TMR-T curve. It is found that the TMR ratio at 24 K is 2.3 times higher than that at 300 K for MgO-based MTJs with t = 1.0 nm ͑see Fig.…”

The tunneling magnetoresistance current dependence on cross sectional area, angle and temperature

“…Similar resistance decreases can be observed as a function of a temperature increase since the spin polarization will be changed by changing the temperature. 23 Both an applied current and a temperature change result in a change of the spin polarization of the FM layer in the MTJ. Therefore it would be worthwhile to find a model that uses the changing spin polarization to describe both current and temperature effects.…”

Tuning Magnetic Microstructures of Reference Layer in Magnetic Tunneling Junctions

“…Its tunneling resistance is related to the relative magnetization orientation between the two FM layers [1], [2]. To get higher sensitivity, we need to get a larger magnetoresistance (MR) ratio [3]- [6] and better control of the low field properties [7]- [10], such as the exchange coupling field , coercivity field , etc. In this paper, the effect of the magnetic microstructures in the reference layer in MTJs is studied.…”