The standard specifications for 40- and 100-Gbit/sec Ethernet transmission, as published by the Institute of Electrical and Electronics Engineers (IEEE), is available for free download as part of the IEEE Get Program. As stated on the Get Program's website, "Through the IEEE-SA and industry support, select IEEE standards are available for download, in PDF format, at no charge."
Anyone who agrees to the IEEE's terms of use may download for free the specification officially titled IEEE 802.3ba-2010 IEEE Standard for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment 4: Media Access Control Parameters, Physical Layers and Management Parameters for 40 Gb/s and 100 Gb/s Operation.
Visit the 802.3 page of the IEEE Get Program here to download the 40/100-Gbit Ethernet standard as well as other specifications including the 802.3az Energy Efficient Ethernet and 802.at Power over Ethernet Plus standards.