a SQUID Magnetometer Study of Uniaxially-Stressed Antiferromagnets Dysprosium-Antimony and Gadolinium-Antimony
DySb is one of a class of rare-earth compounds that undergo first-order phase transitions of antiferromagnetism. It has been suggested that the transitions in these compounds are strongly affected by interactions between the electric quadrupole moments of the rare-earth ions. This would make their properties highly sensitive to uniaxial stress which couples to the quadrupole moment via lattice strain. To test this hypothesis magnetic susceptibility experiments were performed on DySb and the related compound GdSb under uniaxial stress. Measurements were made of the effect of compressive uniaxial stress on the transition and on the magnetic susceptibility in the antiferromagnetic and paramagnetic phases. For the experiments a new apparatus was designed and constructed combining a SQUID magnetometer with a uniaxial stress device. The magnetic moment sensitivity in low fields is 1.2 x 10('-8) G cm('3) and the applied force may be measured to a sensitivity of .006 N. Measurements were made in magnetic fields less than 100 Oe and with applied uniaxial stresses of up to 400 MPa (4 Kbar). An improved method of calibrating the magnetometer was devised that corrects for the effects on the calibration constant of sample shape and the presence of a superconducting shield. Results are presented for three single crystals of DySb. Under compressive stress the transition temperature of all three samples shifts upwards at a rate of (1.2 (+OR -) 0.2) x 10('-2) K/MPa and the discontinuity in magnetic moment at the transition is reduced. The transition becomes continuous indicating the existence of a trcritical point above a critical stress which, after correcting for strain inhomogeneity effects, is 350 (+OR-) 40 MPa. In the paramagnetic state compressive stress causes a temperature-dependent increase in the susceptibility. This behavior was fit using two parameters to the prediction of a mean-field model that includes quadrupolar interactions. The mean-field prediction was also compared to the observed behavior of the transition. The antiferromagnet GdSb is isomorphic to DySb but has no quadrupole moment. Under uniaxial stress the transition temperature was observed to shift upwards at a rate of (6.3 (+OR-) 0.2) x 10('-4) K/MPa but no change in the paramagnetic susceptibility could be detected.
- Pub Date:
- Physics: General