A magnetized Gadolinium surface characterized by Scanning Tunneling Microscopy

  Daniel Segre [1]  ,  Henry Realpe [2]  
[1] Jusidman Science Center for Youth, Ben Gurion University of the Negev, Beer Sheba, Israel & Alpha program, Future scientists program.
[2] Department of Physics, Ben Gurion University of the Negev, Beer Sheva, Israel

Over the last decades, nanotechnology has been utilizing a powerful tool, called Scanning Tunneling Microscopy (STM), for analyzing materials to an atomic resolution level. Thanks to it, it has been possible to research, scan and map the material surfaces to a nanometric scale. For this research work Gadolinium (Gd) was chosen because first it is one of the only two ferromagnetic materials for which TCs (surface Curie temperature) has been observed to be greater than TCb (body Curie temperature), making this material to be of particular interest, and second due to the fact that its Curie temperature (TC) is very close to room temperature.

In this research, thin films of ferromagnetic Gadolinium (Gd) were deposited, at room temperature and under ultra high vacuum conditions, on a nonmagnetic transition metal and single crystal Tungsten (W) substrate. Afterwards, using a heating stage, the Gd/W sample was annealed obtaining a smoothed Gd surface. Subsequently, the sample was translated from the heating stage to an especial constructed port in the STM with two permanent strong neodymium magnets in both sides where the sample Gd surface was scanned.

Several STM topography images with different sizes and resolutions were collected.  After analysis of these images, the formed superstructure of the Gd surface was identified as also the surface corrugation, and atom line features were revealed.

The identified Gd surface features and structures were related to the effect of the permanent magnetic field on the tunnelling current while scanning the Gd surface: On the basis of this analysis it was suggested that this magnetic field induces changes and redistributions in the surface density of states of Gd.

 The aim of this study was to acquire a quantitative knowledge of the surface structure-magnetism relationships for this ferromagnetic material. This knowledge is crucial for the development of various industrial, scientific and medical fields that exploit the properties of Gadolinium.