Method for testing local magnetomechanical coupling coefficient of a magnetic material

A method for testing a local magnetomechanical coupling coefficient of a magnetic material, comprising:

• defining a local magnetomechanical coupling coefficient kIT as a square root of a ratio of a magnetic energy Wmag to an input reversible mechanical work Wre, wherein the magnetic energy Wmag is stored in a magnetic material, and
• determining kIT of the magnetic material comprising the following steps:
• 1) applying a saturated magnetic field to transform the magnetic material to a single domain state;
• measuring nano-indentation load-depth curves comprising a first unloading curve and a first loading curve of the magnetic material;
• integrating the first unloading curve and the first loading curve as functions of depth thereof respectively to obtain a reversible work Wres and a total work Wtots, in the single domain state;
• and recording a ratio of the reversible work Wres to the total work Wtots as C;
• 2) applying an unsaturated magnetic field to transform the magnetic material to a multi-domain state;
• measuring nano-indentation load-depth curves comprising a second unloading curve and a second loading curve of the magnetic material;
• integrating the second unloading curve and the second loading curve as functions of depth thereof respectively to obtain an unloading work Wreu and a total work Wtotu in the multi-domain state;
• and recording the ratio of the unloading work Wreu to the total work Wtotu as d;
• and
• 3) obtaining the local magnetomechanical coupling coefficient of the magnetic material according to the following equation:
• k
• IT
• =
• d
• -
• C
• d
• ⁡
• (
• 1
• -
• C
• )
• .