# Magnetism, structure and chemical order of small FeRh alloy clusters

Alloying elements with complementary qualities has been a major route in material development since the antiquity. In this project we investigate the structural, electronic and magnetic properties of small *Fe _{m}Rh_{n}* clusters having

*N = m + n ? 8*atoms in the framework of a generalized-gradient approximation to density-functional theory. The correlation between structure, chemical order, and magnetic behavior is analyzed as a function of size and composition in view of tailoring their physical behavior for specic technological purposes. Examples of some of the considered geometries are given below. The

*3d-3d*and

*3d-4d*transition metal alloys are particularly interesting since they open the possibility of combining the high stability of

*3d*magnetism with the stronger spin-orbit in-teraction and resulting magnetic anisotropy energies of the heavier

*4d*or

*5*

*d*elements.

*FeRh*in particular shows a very rich phase diagram in the thermodynamic limit whose size dependence deserves special attention.

The calculations show that the bonding resulting from *FeRh *nearest neighbor pairs is stronger than *RhRh* or *FeFe* bonds. For the rich *Fe* concentration, when the number of weaker *FeFe* bonds dominates, one observes that binding energy decreases with increasing *m*.

The average magnetic moment *µ _{N}* of

*Fe*increases monotonically, more or less linearly, with the number of

_{m}Rh_{n}*Fe*atoms. This is a consequence of the larger

*Fe*local moments and the underlying ferromagnetic like magnetic order. Notice, in particular, the enhancement of the magnetic moments of the pure clusters in particular for

*Fe*

_{N }(m = N)*which go well beyond 3µ*

*,*_{B}, the value corresponding to a saturated

*d*-band in the d

^{7}s

^{1 }conguration. In contrast, the moments of pure

*Rh*are far from saturated except for

_{N}*N = 2*and

*7*.

Further details may be found in the reference below. An extension of this work concerning the other materials and optimization methods is currently underway.

[1] J. H. Mokkath and G. M. Pastor, First principles study of magnetism, structure and chemical order in small *FeRh* alloy clusters, submitted to Phys. Rev. B. (2011)