Thickness and angular dependence of the magnetocurrent of hot electrons in a magnetic tunnel transistor with crossed anisotropies

We have studied the thickness and angular dependence of the magnetocurrent of hot electrons in a magnetic tunnel transistor (MTT) with crossed magnetic anisotropies. In a first step, we show that the magnetocurrent increases with ferromagnetic layer thickness as for MTTs with collinear magnetic configurations. The maximum magnetocurrent value is obtained to be 85%, which is close to the theoretical maximum value of 100% for MTTs with crossed magnetic configurations. In a second step, we demonstrate that we are able to reproduce both current vs field direction and current vs field intensity measurements in a framework taking into account a reduced number of magnetic parameters and a simple cosine dependence of the hot-electron current on the angle between magnetizations.

Figure 1

Schematic band diagram of MTT on N-Si for hot-electron injection. Voltage across the MgO tunnel barrier controls the injection energy of the hot electrons.

Figure 2

Measurements done at 50 K on a Si//Cu(5)Ta(1)Cu(5) Ni(0.6)[Co(0.2/Ni(0.6)]4Cu(3.5)Co(3)MgO(2.8)Cu(20)Pt(5) MTT. (a) Variation of the collected current as a function of applied field, with the field applied in plane and applied voltage of 1 V. (b) Current collected in Si as a function of the voltage applied for the parallel magnetic configuration (red curve) and for the crossed magnetic configuration (green curve) of the spin valve. (c) Crossed magnetocurrent as a function of the applied voltage calculated via the curves of the hot-electron current as a function of the applied voltage in the parallel and the crossed magnetic configurations of the spin valve.

Figure 3

(a) Crossed magnetocurrent $\mathrm{M}{\mathrm{C}}^{\perp }$ as a function of the number of repetition of the [Co/Ni] multilayer at an applied voltage of −1 V, for a $\mathrm{Si}//\mathrm{Cu}\left(5\right)\mathrm{Ta}\left(1\right)\mathrm{Cu}\left(5\right)\mathrm{Ni}\left(0.6\right)[\mathrm{Co}{\left(0.2/\mathrm{Ni}\left(0.6\right)\right]}_{\mathrm{N}}\mathrm{Cu}\left(3.5\right)\mathrm{Co}\left(3\right)\mathrm{MgO}\left(2.8\right)\mathrm{Cu}\left(20\right)\mathrm{Pt}\left(5\right)\mathrm{MTT}$. The temperature is 50 K. (b) Calculated variation of the collinear magnetocurrent $\mathrm{M}{\mathrm{C}}^{\mathrm{col}}$ and of the crossed magnetocurrent $\mathrm{M}{\mathrm{C}}^{\perp }$ as a function of $I_{\mathrm{C}}^{\mathrm{P}}/I_{\mathrm{C}}^{\mathrm{AP}}$.

Figure 4

Definition of the angles using for the experiments performed in the last part of the paper. ($X,Y$) is the plane of the sample.

Figure 5

$I_{\mathrm{c}}$ vs $H_{\mathrm{app}}$ measured at 60 K and at 1 V of injection bias, with an in-plane field (orange curve) and an out-of-plane field (blue curve). Continuous lines correspond to fits performed using the model under discussion.

Figure 6

Collected current $I_{\mathrm{c}}$ as a function of the field angle ${\phi }_{H\mathrm{app}}$, measured at 60 K and for an applied voltage $V_{\mathrm{e}}=-1\mathrm{V}$. The magnitude of the applied field is 200, 1000, 3000, or 5000 Oe. Continuous lines correspond to fits performed using the model under discussion.