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Epitaxial PrCo7 films with high energy density


Research on RE-Co magnets with a TbCu7 structure has been intensified in recent years because of their potential as permanent magnets for high temperature applications. RECo7 magnets posses a unique combination of intrinsic properties such as a high saturation polarization, a high Curie temperature and a large uniaxial anisotropy at room temperature. However, the hexagonal RECo7 is a metastable structure and often cannot be prepared without a stabilizing element, to avoid the stable rhombohedral RE2Co17 structure with planar magnetocrystalline anisotropy upon applying higher temperature.

By using the non-equilibrium pulsed laser deposition (PLD) growth technique, we are able to prepare binary epitaxial Pr-Co films with a disordered PrCo7 structure (TbCu7 type) without the addition of any stabilizing element and therefore high saturation polarization. These Pr-Co films are prepared on a Cr buffered MgO(110) substrate at temperature of 450°C to 600°C and grow epitaxially with a (10-10) texture and single orientation of the c-axis of the hexagonal Pr-Co grains along the MgO[001] substrate edge. These PrCo7 films exhibit a energy product value of (BH)max = 345 kJ/m3, which is the highest value ever reported for a RE-Co magnet (Patra JPD'07).

                                           

By varying the Pr concentration between 9 and 27 at%, epitaxial Pr-Co films have been prepared with comparable epitaxial texture but different crystal structures (PrCo7, PrCo5 and Pr2Co7) and spin reorientation transitions.  A magnetic and structural phase diagram for epitaxial Pr-Co films has been established.

 

selected publications:

  • E. Stilp, F. Freudenberger, M. Seifert, A.K. Patra, S. Menzel, I. Mönch, L. Schultz, V. Neu, Probing the anisotropy constants of SmCo5 and PrCo5 by Hall resistance measurements in pulsed high magnetic fields up to 47 T, J. Magn. Magn. Mater. 234, 1711 (2012).

  • A.K. Patra, M. Eisterer, R. Biehle, S. Fähler, L. Schultz, and V. Neu, The temperature dependent anisotropy contants of epitaxially grown PrCo5+x, J. Appl. Phys. 108, 073912 (2010).

  • A.K. Patra, V. Neu, S. Fähler, and L. Schultz, Thermal stability of metastable, epitaxial PrCo7 films with high energy density, J. Phys. D: Applied Phys. 40, 7261 (2007).
  • A.K. Patra, V. Neu, S. Fähler, R. Groetzschel, S. Bedanta, W. Kleemann, and L. Schultz, Crystal structure and its correlation with intrinsic and extrinsic magnetic properties of epitaxial hard magnetic Pr-Co films, Phys. Rev. B 75, 184417 (2007)
  • A.K. Patra, V. Neu, S. Fähler, R. Groetzschel, and L. Schultz, Metastable, epitaxial PrCo7 films with high energy product, Appl. Phys. Lett. 89, 142512 (2006).