| Popis: |
We investigated the structural and magnetic properties of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 alloys fabricated by arc melting. Substitution of Ni by Fe, Co and Cu causes lattice expansions consistent with increasing atomic sizes. The zero-field cooled and field cooled results show second-order magnetic transition at the high-temperature austenite phase to a first-order magnetic transition in the low-temperature martensite phase. The substitution of Ni by Fe and Co increases the austenite Curie temperature TCA from 282 K to 289 K and 294 K respectively while Cu reduces it to 278 K. The martensitic transition temperature TM increased from 221 K to 241 K for Fe substitution and decreased to 210 K and 209 K for Co and Cu respectively. The coercive field HC increased significantly from 457 Oe for Ni at 100 K to 729 Oe for Co at 80 K. The increase to 763 Oe for Fe and 769 Oe for Cu occurred at the same temperature of 40 K. We attribute such increases to domain wall pinning effects due to the inclusions of Fe, Co and Cu. The HC exhibited an anomalous temperature dependence in all the samples. The exchange bias field HEX also showed a significant enhancement below 40 K from 196 Oe for Ni to 476 Oe, 430 Oe and 434 Oe for Fe, Co, and Cu substitutions respectively. The fits to the temperature dependence of the HC reveal significant changes in the competition between ferromagnetic and antiferromagnetic interactions. The peak magnetic entropy change ΔSMpk has a linear dependence on the magnetic field H2/3. The highest value of 28.8 J kg-1 K−1 for ΔSM is obtained in the first order magnetic transition compared to 3.0 J kg-1 K−1 in the second order transition. We report an effective cooling power of 155 J kg-1 in the second order magnetic transition. |
