Magnetic properties of ball-milled Nd2Fe14B-Gd two-phase magnets

Full text: Two-phase (exchange-spring) magnets have been the subject of great interest to many research groups around the world. These magnets contain 10-20vol% of a hard magnetic material ferromagnetically exchange coupled to a matrix of soft magnetic material. These composite magnets exhibit high coercivities and energy products while being less prone to oxidation and cheaper to produce than the single phase hard magnetic material. In our investigation, we have synthesised samples with composition 20vol% Nd2Fe14B (hard phase) and 80vol% Gd (soft phase) by ball milling for different milling times. The magnetic properties of the powders were measured with a SQUID magnetometer and Moessbauer spectroscopy. The combination of Nd2Fe14B and Gd would allow separate microscopic magnetisation measurements to be performed while also allowing measurements to be easily made above the Curie temperature of the soft phase Gd. Magnetometer measurements on one of the samples yielded a temperature dependence relationship of coercivity. This was attributed to the variation of the easy axis direction in Gd with temperature. Moessbauer spectroscopy of the soft phase showed that a distribution of hyperfine fields was present in the material while measurements on the hard phase showed preferential cleavage of planes at z = 1/4