Room-Temperature Low-Field Colossal Magnetoresistance in Double-Perovskite Manganite

We have discovered room-temperature low-field colossal magnetoresistance (CMR) in an $A$-site ordered ${\mathrm{NdBaMn}}_2{\mathrm{O}}_6$ crystal. The resistance changes more than 2 orders of magnitude at a magnetic field lower than 2 T near 300 K. When the temperature and magnetic field sweep from an insulating (metallic) phase to a metallic (insulating) phase, the insulating (metallic) conduction changes to the metallic (insulating) conduction within 1 K and 0.5 T, respectively. The CMR is ascribed to the melting of the charge and orbital ordering. The entropy change which is estimated from the $B\text{−}T$ phase diagram is smaller than what is expected for the charge and orbital ordering. The suppression of the entropy change is attributable to the loss of the short-range ferromagnetic fluctuation of Mn spin moments, which is an important key of the high temperature and low magnetic field CMR effect.

Figure 1

X-ray oscillation photographs of a ${\mathrm{NdBaMn}}_2{\mathrm{O}}_6$ single crystal around 4 4 0 at (b) 280 K and (c) 310 K. The indices are given for the $\sqrt{2}{a}_p\times \sqrt{2}{a}_p\times c_p$ unit cell, where $a_p$ and $c_p$ are lattice constants of simple tetragonal unit cell shown in (a). Temperature dependence of (d) integrated intensities of 2 3 1.5 and 1.5 2 1 superreflections, (e) electrical resistivity at 0 T, and at 7 T, and (f) magnetization at 0.01 and 7 T. The magnetic field is applied perpendicular to the $c$ axis, and parallel to the electric current in (e).

Figure 2

Temperature dependence of magnetization. Open and solid squares denote warming and cooling runs, respectively. The magnetic field is applied perpendicular to the $c$ axis.

Figure 3

Magnetic field dependence of (a),(b),(e),(f) resistivity and (c),(d),(g),(h) magnetization at several temperatures. Insets in (a) and (f) are (a) and (f) whose vertical scales are linear, respectively. The inset in (b) is an enlarged figure in the increasing run of a magnetic field in (b) around the metal-insulator transition. The resistivity of the inset in (b) is normalized by the resistivity at zero magnetic field (see text).

Figure 4

(a) Phase diagram of ${\mathrm{NdBaMn}}_2{\mathrm{O}}_6$ in the magnetic field temperature plane. Solid circles show the average values of $T_{\mathrm{MI}}$’s for cooling (open squares) and warming (solid squares) runs. The broken line is a fitting curve to the magnetic field dependence of the averaged $T_{\mathrm{MI}}$ (see text). (b) Differential scanning calorimetry around $T_{\mathrm{MI}}$.