Novel phase transition in non-antiferromagnetically ordered crystals of La2CuO4

Abstract

We report the discovery of a new phase diagram in the magnetic fieldtemperature plane for single crystals o£ La2Cu04 that show no sign of antiferromagnetic order. The phase boundary is defined by magnetoresistance and sucseptibility measurements. We discuss several possibilities that may lead to the phase diagram observed.

Properties of La2CuO4 and related compounds

“…10, the presence of a sharp peak [ 4,45 ] in the susceptibility indicates that La2CuO4 undergoes antiferromagnetic ordering at TN~257 K, which has been confirmed by neutron-scattering experiments [46 ] that find three-di- mensional Bragg peaks with unit-cell doubling. As noted earlier, TN is very sensitive to the oxygen content and the highest TN ~ 328 K is achieved by vacuum annealing.…”

“…11 ) reflecting the fieldinduced transition. The origin [45,50] cancels that in the next layer (hidden weak ferromagnetism). However, when a high enough magnetic field perpendicular to the Cu-O planes is applied, the net moment in each layer points in the field direction and produces a weak ferromagnetic (WFM) moment (~3X10 -3 ,ua/Cu at 0 K).…”

“…Susceptibility studies on La2CuO4 powders as a function of oxygen content show that TN vanishes at 6~ 0.03 [4], which is a hole-doping level comparable to that required to suppress antiferromagnetism by divalent-cation substitution for La. (The correct definition of TN is not simple [45,47 ]; however, for simplicity we defined TN as the temperature where Z reaches its maximum.) The out-of-plane susceptibility [45] (ZI) exhibits a more sharply defined peak at TN than does the in-plane susceptibility (Zij).…”

“…(The correct definition of TN is not simple [45,47 ]; however, for simplicity we defined TN as the temperature where Z reaches its maximum.) The out-of-plane susceptibility [45] (ZI) exhibits a more sharply defined peak at TN than does the in-plane susceptibility (Zij).…”

“…In the antiferromagnetically ordered state, the Cu spins align along the c-axis in the Cu-O planes. However, a field-induced transition [45,49], which occurs when a magnetic field is applied perpendicular to the Cu-O planes at T< TN, has been observed. The right panel of fig.…”