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 c rystallographic phase transition at about 276 K. The electrical resistance of Gd-5(Si2Ge2) changes drastically and has significant temperature and mag netic-field hystereses. The magnetoresistance has a negative peak of -26% b etween 274 and 295 K in a 4 T magnetic field, which is associated with the transition from the low-temperature, low-resistance ferromagnetic orthorhom bic to the high-temperature, high-resistance paramagnetic monoclinic phase. The increase of the total resistance upon transformation from the magnetic ally ordered orthorhombic to magnetically disordered monoclinic phase corre lates with the differences between the two crystallographic modifications o f Gd-5(Si2Ge2) The behavior of the electrical resistance as a function of m agnetic field between 262 and 282 K shows the presence of temperature-depen dent critical magnetic fields, which can reversibly transform both the magn etic and crystal structures of the material. The magnetic phase diagram obt ained from the magnetic-field and temperature dependencies of the electrica l resistance of Gd-5(Si2Ge2) is proposed. [S0163-1829(99)06835-6].