Structure and Properties of Nanomaterials from ab initio Studies

 

Xianghong Qian

 

Department of Physics, Colorado State University, Fort Collins, CO 80523, USA

 

Materials on a nanometer scale exhibit unique atomic, electronic, optical and magnetic properties. 

Understanding the interplay between structure and properties of these nanomaterials is critical for

their applications as sensors, nano-devices and coatings.

¡¡

Magnetic nanostructures and multilayers are widely used in computer hard drives.  Fe/W(110) and

Fe/Mo(110) ultrathin films are ideal systems to understand the interplay between structure and

magnetism due to their thermostability, pseudomorphic layer-by-layer growth, and potential application

as perpendicular magnetic recording media.

¡¡

We have investigated the atomic structure, magnetic moment and magnetocrystalline anisotropy

of Fe/W(110) ultrathin films employing the highly accurate full-potential linearized augmented plane-wave

(FP-LAPW) method.  The surface and interfacial layers exhibit strong relaxations. 

Significant enhancement of the surface magnetic moment and large interface Fe/W anisotropy were found.  

Surprisingly, Hund¡¯s third rule was found to be violated for W atoms confirmed by recent experimental observations. 

¡¡

It has been demonstrated that surface stress plays an important role in surface diffusion, reconstruction,

morphology, and magnetic domains.  Surface stress also affects nano-device applications due to

the large surface to volume ratio in nanomaterials.  However, surface stress is very difficult to

 measure and quantify.  To date, it has not been  possible to measure surface stress on a bare substrate directly. 

We have developed a composite elastic model and applied this model to calculate theoretically

the surface stress of 7 monolayer (ML) Mo(001) thin films.  Relaxation was found to reduce

surface stress by as much as 40%.