Click on CrossRef's Free DOI Lookup .
Then enter the family name of the First Author, words in the Title of the Journal, the Volume, Page and Year etc. Don't try to fill in all of the fields !
Then hit the Search button and look to the bottom of the resulting form; it should contain a link such as http://dx.doi.org/10.1103/PhysRevB.20.4612 that you can click to obtain the abstract with a link to a PDF file of the complete paper if it exists.
You will only be able to download the complete paper if your computer is licensed for that particular
journal. Computers within the ILL/ESRF domain will usually be licensed for all journals
to which the ILL/ESRF library subscribes for the electronic version.