Coming Soon in Physics

  • Straightening out entanglement
  • Localization physics in graphene

Now in Focus

Quarks Influenced by Their Neighborhood

November 20, 2009

The quark structure inside protons and neutrons changes based on the local nuclear environment, according to electron accelerator experiments.

Feedback

Let us know what you think of Physics. Please email physics@aps.org with your comments, ideas, or suggestions for topics.

APS » Journals » Physics » Synopses » Cooling with magnets

Cooling with magnets

synopsis image

Origin and tuning of the magnetocaloric effect in the magnetic refrigerant Mn1.1Fe0.9(P0.8Ge0.2)

Danmin Liu, Ming Yue, Jiuxing Zhang, T. M. McQueen, Jeffrey W. Lynn, Xiaolu Wang, Ying Chen, Jiying Li, R. J. Cava, Xubo Liu, Zaven Altounian, and Q. Huang

Phys. Rev. B 79, 014435 (Published January 26, 2009)


  Magnetism


A magnetically ordered crystal can act as a refrigerant by absorbing the heat necessary to disorder its spins. Magnetic cooling via this magnetocaloric effect can reach sub-Kelvin temperatures.

In an article appearing in Physical Review B, Danmin Liu of the Beijing University of Technology, Robert Cava of Princeton University, Jeffrey Lynn of NIST, and collaborators in China, Canada, and the United States study various compositions of the promising refrigerant Mn1+yFe1-y(P1-xGex) with neutron diffraction and magnetization measurements. They find that temperature or a magnetic field can drive a first-order phase transition between a paramagnetic and ferromagnetic phase. The magnetic entropy change between these phases—a measure of the efficiency of the magnetocaloric effect—is determined by the degree of completeness of the conversion from one phase to the other. The composition Mn1.1Fe0.9(P0.8Ge0.2) exhibits a magnetic entropy change of about 74 J/kg K, which is among the highest achieved.

Although a record magnetocaloric efficiency was engineered by appropriately tuning the concentration of Ge, there are still inhomogeneities in the distribution of Ge, and the conversion from one phase to another is not complete. These findings suggest that by perfecting the recipe, an even larger magnetocaloric effect should be possible in this material. – Alexios Klironomos