Abstract
We have observed successive magnetic phase transitions in a La2CoO4 single crystal by neutron scattering measurements. Antiferromagnetic long-range order of the La2NiO4 type, [100], S[100], is observed with Néel temperature TN=275 K in the orthorhombic (Cmca) phase. As the temperature is lowered, a first-order phase transition to a new tetragonal phase is found at T2135 K. This structural phase transition is accompanied by a Co2+ (S=32) spin rotation or flip in the CoO2 plane which results in a new spin structure with the spin direction S perpendicular to, the propagation vector of the antiferromagnetic structure. The spin direction itself of this phase cannot be determined uniquely due to the tetragonal symmetry and indeed the most likely structure is noncollinear. In contrast to the S=12 Heisenberg system La2CuO4, well-defined, two-dimensional Ising critical phenomena are observed and the two-dimensional spin correlations at T>TN are almost entirely elastic.
Original language | English |
---|---|
Pages (from-to) | 2336-2343 |
Number of pages | 8 |
Journal | Physical Review B |
Volume | 39 |
Issue number | 4 |
DOIs | |
State | Published - 1989 |
Externally published | Yes |