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 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.
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).