Metamagnetic transition in EuFe${}_2$As${}_2$ single crystals

Abstract

We report the measurements of anisotropic magnetization and magnetoresistance on single crystals of EuFe${}_2$As${}_2$, a parent compound of ferro-arsenide high-temperature superconductor. Apart from the antiferromagnetic (AFM) spin-density-wave transition at 186 K associated with Fe moments, the compound undergoes another magnetic phase transition at 19 K due to AFM ordering of Eu${}^{2+}$ spins ($J=S=7/2$). The latter AFM state exhibits metamagnetic transition under magnetic fields. Upon applying magnetic field with $H\parallel c$ at 2 K, the magnetization increases linearly to 7.0 $\hat{I}{¼}_B$/f.u. at $\hat{I}{¼}_{0}H$=1.7 T, then keeps at this value of saturated Eu${}^{2+}$ moments under higher fields. In the case of $H\parallel ab$, the magnetization increases step-like to 6.6 $\hat{I}{¼}_B$/f.u. with small magnetic hysteresis. A metamagnetic phase was identified with the saturated moments of 4.4 $\hat{I}{¼}_B$/f.u. The metamagnetic transition accompanies with negative in-plane magnetoresistance, reflecting the influence of Eu${}^{2+}$ moments ordering on the electrical conduction of FeAs layers. The results were explained in terms of spin-reorientation and spin-reversal based on an $A$-type AFM structure for Eu${}^{2+}$ spins. The magnetic phase diagram has been established.

10 pages, 8 figures. accepted for publication in New Journal of Physics as a special issue article