Research Interests

Theoretical Condensed Matter Physics

The importance of spin-polarized transport in magnetic nanostructures, e.g., magnetic multilayers, magnetic tunneling junctions, magnetic granular systems, and magnetic semiconductors, has been increasingly realized.  Not only these systems are fundamentally interesting for physicists to study transport properties in new mesoscopic regions, they are essential building blocks for the information technology application (magnetoresistive heads, magnetic random access memory, magnetic recording media, etc.). Our primary research objective is two-folds: to develop a general theoretical framework of the spin-polarized transport in various magnetic nanostructures and to apply theoretical models to a number of important mesoscopic magnetic devices.

Several theoretical approaches, such as, Kubo's linear response, the Boltzmann equations, and the Landauer's formalism, are taken to evaluate transport coefficients in small magnetic structures. We particularly focus on the effects of spin and size dependence in our calculations since they play vital roles in understanding magnetic and transport properties in magnetic nanostructures.

Another project is to study magnetic interactions at magnetic interfaces between different magnetic (ferromagnetic as well as antiferromagnetic) materials. Since interface magnetic structures are ill-known at present time, we are calculating the measurable magnetic properties by assuming a number of interface magnetic profiles. By comparing with experimental data, we are able to determine what is the best model to describe a realistic magnetic interface.

S. Zhang and P. M. Levy, Models for Magnetoresistance in Tunnel Junctions, The European Physical Journal B 10, 599 (1999).

S. Zhang, Electron Screening in Ferromagnetic Surfaces and Magnetic Tunnel Junctions, Physical Review Letters, 83, 640 (1999).

S. Zhang, D. V. Dimitrov, G. C. Hadjipanayis, J. W. Cai, and C. L. Chien, Coercivity Induced by Random Field at Ferromagnetic and antiferromagnetic interfaces, Journal of Magnetism and Magnetic Materials, 198, 469 (1999).

S. Zhang and P. M. Levy, Magnetoresistance of Magnetic Tunnel Junctions in the Presence of a Nonmagnetic Layer, Physical Review Letters, 81, 5660 (1998).

D. V. Dimitrov, S. Zhang, J. Q. Xiao, G. C. Hadjipanayis, and C. Prados, Effect of Exchange Interactions at Antiferromagnetic/ferromagnetic Interfaces on Exchange Bias and Coercivity, Physical Review B 58, 12090 (1998).

D. Kent, U. Ruediger, J. Yu, S. Zhang, P. M. Levy, Y. Zhong and S. S. P. Parkin, Magnetoresistance Due to Domain Walls in Micro Scale Fe Wires with Stripe Domains,

 IEEE Transactions on Magnetics 34, 900 (1998).

K. Wang, S. Zhang, P. M. Levy, S. Laszlo and P. Weinberger, Role of Electronic Structure in Magnetic Tunneling, Journal of Magnetism and Magnetic Materials, 189, 131 (1998).

U. Ruediger, J. Yu, S. Zhang, A. D. Kent, and S. S. P. Parkin, Negative Domain Wall Contribution to the Resistivity of Microfabricated Fe Wires, Physical Review Letters 80, 5637 (1998).

S. Zhang and P. M. Levy, Interplay of Specular and Diffuse Scattering, Physical Review B57, 5336 (1998).

P. M. Levy and S. Zhang, Resistivity Due to Domain Wall Scattering, Physical Review Letters 79, 5110 (1997).

S. Zhang, P. M. Levy, A. C. Marley and and S. S. P. Parkin, Quenching of Magnetoresistance by Hot electrons in Magnetic Tunnel Junctions, Physical Review Letters 79, 3744 (1997).

P. M. Levy and S. Zhang, Current Status of Our Understanding of Magnetotransport in Magnetic Multilayers, Journal of Magnetism and Magnetic Materials 164, 284 (1997).