Direct and indirect measurement of magnetocaloric effect in NiCoMnGa alloys

The Co-substitution for Ni in the Mn-rich NiMnGa Heusler alloys changes substantially their structural and magnetic ordering. The results will be discussed within the basic thermodynamic relations

Co and In Doped Ni-Mn-Ga Magnetic Shape Memory Alloys: A Thorough Structural, Magnetic and Magnetocaloric Study

In Ni-Mn-Ga ferromagnetic shape memory alloys, Co-doping plays a major role in determining a peculiar phase diagram where, besides a change in the critical temperatures, a change of number, order and nature of phase transitions (e.g., from ferromagnetic to paramagnetic or from paramagnetic to ferromagnetic, on heating) can be obtained, together with a change in the giant magnetocaloric effect from direct to inverse. Here we present a thorough study of the intrinsic magnetic and structural properties, including their dependence on hydrostatic pressure, that are at the basis of the multifunctional behavior of Co and In-doped alloys. We study in depth their magnetocaloric properties, taking advantage of complementary calorimetric and magnetic techniques, and show that if a proper measurement protocol is adopted they all merge to the same values, even in case of first order transitions. A simplified model for the estimation of the adiabatic temperature change that relies only on indirect measurements is proposed, allowing for the quick and reliable evaluation of the magnetocaloric potentiality of new materials starting from readily available magnetic measurements

Investigation of the pressure and temperature dependence of the intrinsic magnetic properties of YCo 4Ge

International audienceThe YCo 4Ge intrinsic magnetic properties; such as the saturation magnetization and the magnetocrystalline anisotropy parameters; are determined at 5, 100, 200 and 300 K from a fit of the isothermal magnetization curves measured in applied field up to 10 T. Ge for Co substitution induces a reduction of the first order anisotropy parameter as well as of the uniaxial anisotropy field. At 4 K an anisotropy field of 5.8 T is obtained, whereas a value of that is observed at room temperature. The magnetocrystalline anisotropy found for YCo 4Ge is significantly reduced upon heating from 4 to 300 K. The investigation of the magnetic properties of YCo 4Ge in both the ordered and the paramagnetic phases shows that this YCo 4Ge compound exhibits a typical itinerant ferromagnetic behavior. The effect of applied pressure on the isothermal magnetization has been investigated showing that the volume has an important influence on the magnetization of YCo 4Ge. The influence of the Ge for Co substitution on the Co-Co exchange interaction is also discussed. The results are compared and commented on in the light of earlier reports for YCo 5 and other Co containing phases

Magnetic and magnetocaloric properties of partially disordered RFeAl (R = Gd, Tb) intermetallic

International audienceMagnetic and magnetocaloric properties of TbFeAl and GdFeAl were studied in a wide temperature region in magnetic field up to 10 T. They order magnetically below Tc ¼ 196 K and 259 K for TbFeAl and GdFeAl, respectively. The temperature change of DT ¼ 1.4 K and 1.6 K was observed in GdFeAl and TbFeAl respectively for a field change of 4 T. Interestingly wide temperature region of significant magnetocaloric effect was observed in both compounds which give rise to relative cooling power of 350 J kg 1 for TbFeAl and 348 J kg 1 for GdFeAl for 4 T field span