Lithographically and electrically controlled strain effects on anisotropic magnetoresistance in (Ga,Mn)As

It has been demonstrated that magnetocrystalline anisotropies in (Ga,Mn)As are sensitive to lattice strains as small as 10^-4 and that strain can be controlled by lattice parameter engineering during growth, through post-growth lithography, and electrically by bonding the (Ga,Mn)As sample to a piezoelectric transducer (PZT). In this work, we show that analogous effects are observed in crystalline components of the anisotropic magnetoresistance (AMR). Lithographically or electrically induced strain variations can produce crystalline AMR components which are larger than the crystalline AMR and a significant fraction of the total AMR of the unprocessed (Ga,Mn)As material. In these experiments, we also observe new higher order terms in the phenomenological AMR expressions which were previously unnoticed in (Ga,Mn)As. It is demonstrated that strain variation effects can play an important role in the magnetotransport characteristics of (Ga,Mn)As lateral nanoconstrictions.