From soft to hard magnetic Fe–Co–B by spontaneous strain: a combined first principles and thin film study

In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline anisotropy which may compete with shape anisotropy. To probe this theoretical suggestion experimentally, epitaxial films are examined. A spontaneous strain up to 5% lattice distortion is obtained for B content up to 4 at%, which leads to uniaxial anisotropy constants exceeding 0.5 MJ m(-3). However, a further addition of B results in a partial amorphisation, which degrades both anisotropy and magnetisation.

[1]  H. Monkhorst,et al.  SPECIAL POINTS FOR BRILLOUIN-ZONE INTEGRATIONS , 1976 .

[2]  J. Kirschner,et al.  Strongly enhanced orbital moment by reduced lattice symmetry and varying composition of Fe1-xCox alloy films. , 2008, Physical review letters.

[3]  H. Okamoto.  Co-Fe (Cobalt-Iron) , 2008 .

[4]  J. Morral,et al.  The solubility of boron in iron , 1986 .

[5]  M. Przybylski,et al.  Tuning the perpendicular magnetic anisotropy in tetragonally distorted FexCo1−x alloy films on Rh (001) by varying the alloy composition , 2007 .

[6]  W. R. Thomas,et al.  Condition of Boron in Alpha Iron , 1955, Nature.

[7]  Ruban,et al.  Madelung energy for random metallic alloys in the coherent potential approximation. , 1995, Physical review. B, Condensed matter.

[8]  A. Lucci,et al.  Comments on the condition of boron in α-iron , 1971 .

[9]  Dan H. R. Fors,et al.  Nature of boron solution and diffusion in α -iron , 2008 .

[10]  Helmut Eschrig,et al.  The effect of chemical disorder on the magnetic anisotropy of strained Fe–Co films , 2011, 1103.5303.

[11]  F. Pfeifer,et al.  Soft magnetic Ni-Fe and Co-Fe alloys - some physical and metallurgical aspects , 1980 .

[12]  M. Yamaguchi,et al.  Effects of boron contents on magnetic properties of Fe-Co-B thin films , 2004, IEEE transactions on magnetics.

[13]  G. Kresse,et al.  Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set , 1996 .

[14]  R. C. Hall.  Magnetic Anisotropy and Magnetostriction of Ordered and Disordered Cobalt-Iron Alloys , 1960 .

[15]  A. Ludwig,et al.  The Bain library: A Cu-Au buffer template for a continuous variation of lattice parameters in epitaxial films , 2014 .

[16]  L. Benedict,et al.  Origin of the spin reorientation transitions in (Fe1–xCox)2B alloys , 2015, 1501.03483.

[17]  M. Richter,et al.  Full tunability of strain along the fcc-bcc bain path in epitaxial films and consequences for magnetic properties. , 2009, Physical review letters.

[18]  Morris Cohen,et al.  Self diffusion in iron , 1961 .

[19]  L. Vitos.  Computational Quantum Mechanics for Materials Engineers: The EMTO Method and Applications , 2007 .

[20]  B. Johansson,et al.  Calculated magnetic properties of binary alloys between Fe, Co, Ni, and Cu , 1999 .

[21]  B. Min,et al.  Boron solution and distribution inα-Fe: Application to boron steel , 2010 .

[22]  R. Hasiguti,et al.  Internal Friction of Alpha-Iron Due to Boron Atoms , 1954 .

[23]  Budapešť,et al.  Application of the exact muffin-tin orbitals theory: the spherical cell approximation , 2000, cond-mat/0005313.

[24]  T. M. Crawford,et al.  Stress dependence of soft, high moment and nanocrystalline FeCoB films , 2002 .

[25]  M. Futamoto,et al.  Effects of film composition and substrate orientation on the structure and the magnetic properties of Fe-Co-B alloy films formed on MgO single-crystal substrates , 2013 .

[26]  R. Victora,et al.  Calculated magnetization of iron-cobalt disordered alloys , 1984 .

[27]  B. Johansson,et al.  Tetragonality of carbon-doped ferromagnetic iron alloys : A first-principles study , 2012 .

[28]  M. Kuz’min,et al.  Towards high-performance permanent magnets without rare earths , 2014, Journal of physics. Condensed matter : an Institute of Physics journal.

[29]  R. Ray,et al.  Iron‐boron metallic glasses , 1978 .

[30]  P. Strocchi,et al.  On the nature of boron solid solution in α-iron , 1967 .

[31]  Y. Hayashi,et al.  Nature of boron in α-iron , 1970 .

[32]  A. Mookerjee,et al.  Magnetic state effect upon the order-disorder phase transition in Fe-Co alloys : A first-principles study , 2011 .

[33]  Marek Przybylski,et al.  Strong perpendicular anisotropy in Fe 1 − x Co x alloy films epitaxially grown on mismatching Pd(001), Ir(001), and Rh(001) substrates , 2009 .

[34]  A. Sakuma,et al.  Degree of Order Dependence on Magnetocrystalline Anisotropy in Body-Centered Tetragonal FeCo Alloys , 2012, 1210.4386.

[35]  Jan Rusz,et al.  Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain , 2014, 1409.4952.

[36]  B. Johansson,et al.  Anisotropic lattice distortions in random alloys from first-principles theory. , 2001, Physical review letters.

[37]  S. Fähler,et al.  Calculations and experiments of material removal and kinetic energy during pulsed laser ablation of metals , 1996 .

[38]  Kresse,et al.  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. , 1996, Physical review. B, Condensed matter.

[39]  R. O'handley.  Magnetostriction of ferromagnetic metallic glasses , 1977 .

[40]  Jochen Barthel,et al.  Perpendicular magnetic anisotropy induced by tetragonal distortion of FeCo alloy films grown on Pd(001). , 2006, Physical review letters.

[41]  I. Turek,et al.  Magnetic anisotropy energy of disordered tetragonal Fe-Co systems from ab initio alloy theory , 2012, 1210.1028.

[42]  J. Shih.  Magnetic Properties of Iron-Cobalt Single Crystals , 1934 .

[43]  B. L. Gyorffy.  Coherent-Potential Approximation for a Nonoverlapping-Muffin-Tin-Potential Model of Random Substitutional Alloys , 1972 .

[44]  Paul Soven,et al.  Coherent-Potential Model of Substitutional Disordered Alloys , 1967 .

[45]  O. Eriksson,et al.  Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities : A potential new permanent magnet , 2014 .

[46]  G. Kresse,et al.  From ultrasoft pseudopotentials to the projector augmented-wave method , 1999 .

[47]  Blöchl,et al.  Projector augmented-wave method. , 1994, Physical review. B, Condensed matter.

[48]  M. Zwierzycki,et al.  The Overlapping Muffin-Tin Approximation , 2008, 0808.0105.

[49]  Olle Heinonen,et al.  Giant magnetic anisotropy in tetragonal FeCo alloys. , 2004, Physical review letters.

[50]  Ján Minár,et al.  Calculating condensed matter properties using the KKR-Green's function method—recent developments and applications , 2011 .

[51]  H. Skriver,et al.  From ASA Towards the Full Potential , 1999 .

[52]  Third-Generation TB-LMTO , 1998, cond-mat/9804166.

[53]  Olle Eriksson,et al.  Perpendicular magnetocrystalline anisotropy in tetragonally distorted Fe-Co alloys. , 2006, Physical review letters.

[54]  M. Wuttig,et al.  Adaptive modulations of martensites. , 2009, Physical review letters.

[55]  L. Schultz,et al.  Lattice relaxation studies in strained epitaxial Fe-Co-C films , 2015 .

[56]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[57]  Levente Vitos,et al.  Total-energy method based on the exact muffin-tin orbitals theory , 2001 .

[58]  H. Skriver,et al.  Screened Coulomb interactions in metallic alloys. I. Universal screening in the atomic-sphere approximation , 2002, cond-mat/0202370.

[59]  H. Skriver,et al.  Full charge-density scheme with a kinetic-energy correction: Application to ground-state properties of the 4d metals , 1997 .

[60]  F. Tittel,et al.  Portable fiber-coupled diode-laser-based sensor for multiple trace gas detection , 1999, Applied physics. B, Lasers and optics.

[61]  Xin-lai He,et al.  Diffusion of boron in alloys , 1995 .