Thursday, June 23, 2011

Multiferroic Alloy

University of Minnesota scientists have discovered a new alloy that converts heat directly into electricity. In theory, an alloy like this could be used to capture waste heat from a car's exhaust and use it to produce electricity to charge the car's battery. Similarly, a thin film of this alloy could be used to convert waste heat from computers into electricity.
The alloy is made out of nickel, cobalt, manganese and tin and has the formula Ni45Co5Mn40Sn10.
This new alloy undergoes a highly reversible phase transformation in which one solid turns into another solid with very different magnetic properties. This means that the new alloy begins as a non-magnetic material, then suddenly becomes strongly magnetic when the temperature is raised a small amount. When this happens, the material absorbs heat and spontaneously produces electricity in a surrounding coil.
Substances which combine unusual magnetic and electric properties such as this alloy are called multiferroic materials. Other multiferroic materials include TbMnO3, HoMn2O5, LuFe2O4, BiFeO3 and BiMnO3.

In the demonstration below, "University of Minnesota researchers show how a new multiferroic material they created begins as a non-magnetic material then suddenly becomes strongly magnetic as the piece of copper below is heated a small amount. When this happens, it jumps over to a permanent magnet. This demonstration represents the direct conversion of heat to kinetic energy."


Vijay Srivastava, Yintao Song, Kanwal Bhatti, R. D. James. The Direct Conversion of Heat to Electricity Using Multiferroic Alloys. Advanced Energy Materials, 2011; 1 (1): 97 DOI: 10.1002/aenm.201000048

Further Reading
Metals and Non-metals
Physical and Chemical Changes
Pure Substances and Mixtures
Percentage Composition

Study Questions
  1. What is meant by the term "alloy"?
  2. What is meant by the term "multiferroic material"?
  3. Calculate the percentage composition of the following multiferroic materials:
    • TbMnO3
    • HoMn2O5
    • LuFe2O4
    • BiFeO3
    • BiMnO3
    • Ni45Co5Mn40Sn10
  4. Which of the above substances would be classified as alloy(s)? Explain your answer.
  5. Which of the substances in question 3 would be classified as mixture(s)? Explain your answer.
  6. What similarities can you see in the multiferroic materials listed in question 3?
  7. How do you think these similarities contribute to their magnetic and electrical properties?

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