(Ga,Mn)As based superlattices and the search for antiferromagnetic interlayer coupling

Antiferromagnetic interlayer coupling in dilute magnetic semiconductor superlattices could result in the realization of large magnetoresistance effects analogous to the giant magnetoresistance seen in metallic multilayer structures. In this paper we use a mean-field theory of carrier induced ferromagnetism to explore the multidimensional parameter space available in (Ga,Mn)As based superlattice systems. Based on these investigations we examine the feasibility of creating a superlattice that exhibits antiferromagnetic coupling and suggest potentially viable recipes.

Figure 1

(Color online) The self-consistent charge distribution, $N_{3\text{D}}$, and potentials, $V_{\sigma }$, for a double unit cell of three different (Ga,Mn)As/GaAs based superlattice structures in an AFM state. $d_m/\frac{1}{2}{a}_0=2$, $d_n/\frac{1}{2}{a}_0=5$, and ${\overline{N}}_{3\text{D}}={10}^{20}{\text{cm}}^{-3}$ in each case. $V_{\sigma }=0\text{eV}$ corresponds to the Fermi level. (a) 2% Mn doping and a uniform impurity concentration, (b) 8% Mn doping and a uniform impurity concentration, and (c) 2% Mn doping but no impurities in the nonmagnetic layer.

Figure 2

(Color online) The self-consistent charge distribution, $N_{3\text{D}}$, and potentials, $V_{\sigma }$, for a double unit cell of three different (Ga,Mn)As/(Al,Ga)As based superlattice structures in an AFM state. $d_n/\frac{1}{2}{a}_0=5$, ${\overline{N}}_{3\text{D}}={10}^{20}{\text{cm}}^{-3}$, and the Al concentration is 30% in each case. $V_{\sigma }=0\text{eV}$ corresponds to the Fermi level. (a) $d_m/\frac{1}{2}{a}_0=2$ and 2% Mn doping, (b) $d_m/\frac{1}{2}{a}_0=2$ and 8% Mn doping, and (c) $d_m/\frac{1}{2}{a}_0=8$ and 8% Mn doping.

Figure 3

(Color online) The IEC energy, $E_c$, of two (Ga,Mn)As/GaAs based superlattices as a function of the average 3D carrierconcentration, ${\overline{N}}_{3\text{D}}$, and the number of monolayers of nonmagnetic layer, $d_n/\frac{1}{2}{a}_0$. Positive (red colored) values of $E_c$ indicate FM interlayer coupling is energetically favorable and negative (blue colored) values indicate AFM is favorable. Both superlattices have a 2% Mn doping in the magnetic layer and there is a uniform impurity concentration of acceptors through the structure.

Figure 4

(Color online) IEC energy, $E_c$, as a function of $2{\overline{k}}_F{d}_{n+1}$ for a superlattice with magnetic layers with a Mn doping of 2% and two monolayer thickness, and a uniform impurity concentration. The (red) curve is an estimate of the ideal RKKY range function.

Figure 5

(Color online) The IEC energy, $E_c$, of two (Ga,Mn)As/GaAs based superlattices as a function of the average 3D carrierconcentration, ${\overline{N}}_{3\text{D}}$, and the number of monolayers of nonmagnetic layer, $d_n/\frac{1}{2}{a}_0$. Both superlattices have an 8% Mn doping in the magnetic layer and there is a uniform impurity concentration of acceptors through the structure.

Figure 6

(Color online) The IEC energy, $E_c$ of two (Ga,Mn)As/GaAs based superlattices as a function of the average 3D carrier concentration, ${\overline{N}}_{3\text{D}}$, and the number of monolayers of nonmagnetic layer, $d_n/\frac{1}{2}{a}_0$. Both superlattices have a 2% Mn doping in the magnetic layer, but there is no charge doping in the nonmagnetic spacer layer.

Figure 7

(Color online) The IEC, $E_c$, of two (Ga,Mn)As/(Al,Ga)As based superlattices as a function of the average 3Dcarrier concentration, ${\overline{N}}_{3\text{D}}$, and the number of monolayers of nonmagnetic layer, $d_n/\frac{1}{2}{a}_0$. Both superlattices have a 2% Mn doping in the magnetic layer and the nonmagnetic layers are $\left({\text{Al}}_{0.3},{\text{Ga}}_{0.7}\right)\text{As}$ and have no charge doping.

Figure 8

(Color online) The IEC, $E_c$, of two (Ga,Mn)As/(Al,Ga)As based superlattices as a function of the average 3D carrier concentration, ${\overline{N}}_{3\text{D}}$, and the number of monolayers of nonmagnetic layer, $d_n/\frac{1}{2}{a}_0$. Both superlattices have an 8% Mn doping in the magnetic layer and the nonmagnetic layers are $\left({\text{Al}}_{0.3},{\text{Ga}}_{0.7}\right)\text{As}$ and have no charge doping.

Figure 9

(Color online) A comparison of the IEC energy, $E_c$, as afunction of the average 3D carrier concentration, ${\overline{N}}_{3\text{D}}$, for two specific superlattices with either a GaAs or an $\left({\text{Al}}_{0.3},{\text{Ga}}_{0.7}\right)\text{As}$ nonmagnetic layer. The magnetic layers are eight monolayers thick and have a Mn concentration of $5\times {10}^{20}{\text{cm}}^{-3}$ (2.26%) and the nonmagnetic layers are four monolayers thick.