Magnetic Phase Transition and Magnetic Structure of Ca$_{3}$Ru$_{2}$O$_{7}$

Ca$_{3}$Ru$_{2}$O$_{7}$ shows exciting physical properties, including a bulk spin-valve behavior and orbital ordering.$^{[1-3]}$ We have investigated the magneto-transport properties and the magnetic structure of this material using high-quality Ca$_{3}$Ru$_{2}$O$_{7}$ single crystals grown by a floating-zone (FZ) method. From magnetoresistivity measurements, we observe that the previously reported metamagnetic transition at $\sim $6T for $H//a$ axis consists of two separate transitions occurring at 5.9 and 6.5T, respectively. The first transition is extremely sharp with the transition width less than 1 Gauss, corresponding to the bulk spin-valve behavior, while the second transition has a finite width which is likely associated with the change of orbital polarization. Our elastic neutron scattering measurements on FZ-grown Ca$_{3}$Ru$_{2}$O$_{7}$ single crystals confirm the magnetic structure suggested by previous works,$^{[2, 4]}$ i.e., the magnetic moments align ferromagnetically within the double layers and antiferromagnetically between the double layers. 1. X.N. Lin et al., Phys. Rev. Lett., 95, 017203 (2005). 2. D.J. Singh and S. Auluck, Phys. Rev. Lett., 96, 097203 (2006). 3. J.F. Karpus, et al., Phys. Rev. Lett., 93, 167205 (2004). 4. Y. Yoshida, et al., Phys. Rev. B, 72, 054412 (2005).