Category Archives: Papers

Fallot and Hocart 1939 FeRh Paper

I started looking at FeRh back in 2015 with Gino Hrkac in Exeter and Tom Thomson’s group in Manchester. This interesting material undergoes a change in its magnetic state from antiferromagnetic to ferromagnetic upon changing temperature (other stimuli are also possible). One of the original papers was by Fallot and Hocart and is regularly cited as such in the literature. However, I found that whilst it was well cited, I could not find a copy of the paper. It was often cited as – M. Fallot and R. Horcart, Rev. Sci. 77, 498 (1939). I tried for a while to find out which journal Rev. Sci. was by googling journal abbreviations (e.g. here) but to no avail.

Cover page for volume 77 and page 498 showing the first part of the article by Fallot and Hocart’s on FeRh.
Source / Bibliothèque nationale de France

Eventually, I tracked down the journal, which turned out to be “La Revue Scientifique”, which is a historic French journal founded in 1838 and, interestingly, also known as “La Revue Rose” due to the colour of its cover and in opposition to “La Revue Blue” (the nickname of “La Revue Politique et littéraire”. The particular edition (volume 77) from January 1939 has been scanned and can be found at the following link.


New Paper on Multiscale Modeling of Fe/Ir Interfaces

Today sees the publication of my latest article, published in Scientific Reports. This work involves the use of first principles methods and atomistic spin dynamics to study the magnetic properties of Fe/Ir/Fe sandwiches. Such magnetic systems with interfaces are extremely difficult to model accurately, but by using first and second principles models we have been able to obtain layer-by-layer equilibrium and dynamic properties, which are even trickier to determine experimentally.

Schematic of an Fe/Ir/Fe Sandwich

By using the SIESTA code to structurally relax the interfaces (see schematic) of different Ir, the ground state atomic structure can be found. We then used the Budapest SKKR code to determine an extended Heisenberg Hamiltonian. This complex Hamiltonian has a complete lack of translational invariance perpendicular to the plane, essentially meaning that each Iron plane is in its own environment which interact differently with the others. Our spin dynamics results show that this has important consequences for the equilibrium magnetic properties, as well as the dynamics. We find that the spinwaves are stiffened with increasing temperature, which goes against the thermal effects that usually result in a decrease. This is due to the frustration arising from the exchange at the interface with Ir. Finally, our results reveal a plane-wise dependence of the demagnetisation process.

The work was done in collaboration with international groups including ICN2 (Barcelona), Budapest University of Technology and the Universities of Exeter and York. The work is Open Access meaning that it is free for all to view (see this link). This was made possible due to the Sheffield Hallam University Open Access Fund. I would also like to thank Eddy Verbaan and the Library Research Support Team for their help in obtaining funding to make this article Open Access.



Strain Effects on the Metamagnetic Phase Transition in FeRh on MgO

In a collaboration between the Universities of Manchester and Exeter a new article has been  published today in Scientific Reports. Lead by Dr Craig Barton at the University of Manchester we investigated the role of strain in FeRh layers on MgO.

FeRh goes from antiferromagnetic to ferromagnetic in bulk at around 70°C. However, in thin films this temperature can change depending on the thickness and the material it is interfaced with. In this new article we measured the effect of film thickness on the transition temperature and correlated the effects with changes in the structural properties. We corroborate a number of observations using theoretical models that account for the strain at the interface. The article is open access so anyone can download and read the article here.