1. No need to design and fabricate extra word and bit lines to generate the magnetic fields;

2. Reduced perturbation of neighboring magnetic elements when writing to one bit in an array;

3. The possibility for continued scaling of magnetic bit sizes to the lithography limits of silicon processing, because spin-transfer switching currents can be minimized while independently maintaining the magnetic-anisotropy barriers required for thermal stability;

4. Much less demanding device tolerances, because spin-transfer architectures will not require switching characteristics to be as uniform as field-switching.

However, two main challenges that complicated the immediate applications of spin transfer in memory technologies:

1. All-metal spin-valve devices have low resistances, 1 - 10 Ω, much less than the 1 - 10 kΩ needed to provide reasonable signal-to-noise when a silicon circuit is used to read the magnetic configuration.

2. While the critical currents required to produce magnetic switching have decreased steadily with improvements in device processing, from 5 mA in early Co devices [5] to approximately 0.3 mA in the best existing Py samples, even smaller critical currents would be desirable. Critical currents of 0.1mA would enable control of magnetic bits using minimum-area silicon CMOS transistors, and could make possible very dense memory circuits.

(b) Spin-transfer-driven microwave sources and oscillators:
The microwave frequency dynamical magnetic modes that can be excited by DC spin-transfer torques are under investigation for the use of high-speed signal processing, as nanoscale microwave sources, oscillators, and amplifiers. The precessing spin-transfer devices may be applied as sources and detectors for wireless chip-to-chip communications [6,9]. Some of the key issues that remain to be resolved are similar to the ongoing work in the MRAM devices, e.g., to optimize the devices to achieve maximum signal levels.

(c) Read heads:
In current-perpendicular to the plane giant magnetoresistance based (CPP-GMR) magnetic read heads that are under development for high-density magnetic disk drives, spin-transfer torques can generate noise and reduce the effectiveness of the sensor [10,11]. A full understanding of spin-transfer excitations will therefore be important to minimize these harmful effects.