Magnetic-field and temperature dependencies of the electrical resistance near the magnetic and crystallographic first-order phase transition of Gd-5(Si2Ge2)

The magnetic field (0 to 4 T) and temperature (5 to 320 K) dependencies of the electrical resistance of Gd-5(Si2Ge2) have been measured. Upon heating in zero-magnetic field Gd-5(Si2Ge2) undergoes a simultaneous magnetic and crystallographic phase transition at about 276 K. The electrical resistance of Gd-5(Si2Ge2) changes drastically and has significant temperature and magnetic-field hystereses. The magnetoresistance has a negative peak of -26% between 274 and 295 K in a 4 T magnetic field, which is associated with the transition from the low-temperature, low-resistance ferromagnetic orthorhombic to the high-temperature, high-resistance paramagnetic monoclinic phase. The increase of the total resistance upon transformation from the magnetically ordered orthorhombic to magnetically disordered monoclinic phase correlates with the differences between the two crystallographic modifications of Gd-5(Si2Ge2) The behavior of the electrical resistance as a function of magnetic field between 262 and 282 K shows the presence of temperature-dependent critical magnetic fields, which can reversibly transform both the magnetic and crystal structures of the material. The magnetic phase diagram obtained from the magnetic-field and temperature dependencies of the electrical resistance of Gd-5(Si2Ge2) is proposed. [S0163-1829(99)06835-6].