Magnetic field dependence of the 3D ordering in La2CuO4−δ

Abstract The magnetic field dependence of the three dimensional magnetic ordering transition has been examined in single crystalline La 2 CuO 4−δ by magnetization and magnetoresistance measurements. We establish a phase diagram in the magnetic field-temperature plane and point out similarities to metamagnetic transitions observed in other magnetic systems.

The magnetic field dependence of the three dimensional magnetic ordering transition has been examined in •ingle crystalline La2CuO4.6 by magnetization and magnetoresistance mea•urement•.We e•tabli•h a pha•e diagram in the magnetic fieldtemperature plane and point out similarities to metamagnetlc transitions observed in other magnetic system•.
The unusual magnetic properties of La2Cu04_ 6 have been explored thoroughly by magnetic susceptlbillty I, neutron diffraction 2 and nuclear resonance 3 studies but the detailed nature of the varlou• correlations still is not understood completely.
The static magnetic susceptibility X measured at a relatively low magnetic field has a broad minimum around room temperature, followed by a sharp maximum at Ta with decreasing temperature I.The  T N also strongly depend• on the oxygen content and it is believed that the largest value, T M -290 K, corresponds to 6 -0.03, with T N depressed as the oxygen deficiency decreases 4. The onset of 3D ordering leads to a rather sharp decrease in the electrical resistivity which may be due to a loss of spin disorder scattering.
We report the observation of a magnetic field induced transition at temperature• T < T N from magnetic susceptibility and magnetoresistance(R(H)) studies and establish an H-T phase diagram.
We also point out the .':..   T at 5 Tesla and M(H) vs. H at 170 K, respectively.( See text for details.) A-phase and Cphase are antlferromagnetic and paramagnetic states, respectively: Bphase could be a complex ferromagneticlike state( see text for details).

TEMPERATURE (K)
The vertical and dashed line dividing phases B and C could be more complicated than indicated.

K.
In that study, the anomalies in the M(H) and R(H) curves were less pronounced than those reported here and the magnetic fields at which the transition appeared were found to be small, with a fractional reduction from values given here roughly comparable with the fractional differences in TN.
We discuss the characteristics of these experimental findings.First, although the overall temperature dependence is complicated, just above the ordering transition( 245 K < T < 320 K) the magnetic susceptibility measured in a 0.5 T field can be fit to Xmoz -Xo + C/(Te),3where Xo -4 x 10 -5 emu/mole-f.u.,C -7.9 x i0emu-K/mole-f.u,and 8 -46.4 K, implying an effective magnetic moment per Cu ion of 0.25 ~R 'if the Curie term is due solely to Cu ions.We note that even though the magnetic ordering is antlferromagnetic, O is positive, indicative of the presence of ferromagnetic correlations.The zero field intercept of magnetization extrapolated from the magnetization curve at high fields is not zero and a small hysteresis in the magnetization curve below TN was found in La2CuO4.6, which additionally suggest the transition to be metamagnetic rather than a spin-flop transition.
To check for the possibility of a metamagnetic transition in CuO, which exhibits an antiferromagnetlc ordering transition at 240 K and could be a part of La2CuO4.6 crystals as impurities, specially as an incluson, we measured magnetization curves of CuO crystals at various temperatures but did not find any field induced transition in CuO similar to that reported here. Fig.1

Fig. 2 Fig. 3 Fig. 4 H
Fig. 2 Isothermal magnetization vs. field curves at various fixed temperatures.The solid lines are drawn through the low field data to demonstrate the nonlinear behavior observed.