Magnetic properties of a ferromagnetic double spin chain compound LaCrOS2

Magnetic properties of LaCrOS2, in which Cr ions form zigzag chains, well separated with each other, have been studied. Because the temperature dependence of the inverse magnetic susceptibility above 200 K obeys Curie-Weiss law, we obtain a Weiss temperature Theta(p) of 75 K. The large positive Weiss temperature and the steep increase of the magnetization below 80 K show that ferromagnetic interaction between Cr ions is dominant in this compound. The magnetization curves, however, show no spontaneous magnetization down to 4.2 K. This indicates that Cr ions do not order three dimensionally at least above 4.2 K. The saturation magnetization at 4.2 K is about 2.5 mu(B) per Cr ion. In the low temperature range, the differential magnetic susceptibility chi(d) is expressed approximately as chi(d)=(C/T) exp Delta/(k(B)T), where Delta is equal to 131 K. The temperature dependence of chi(d) at low temperature suggests that a zigzag chain of Cr spins in this compound behave like a one-dimensional ferromagnetic Ising chain which has an excitation gap Delta. A numerical calculation for the ferromagnetic Ising chain with s=3/2 using the transfer matrix method reproduces the temperature dependence of the magnetic susceptibility for the whole temperature range using a g value of 1.91 and a coupling constant J of 28 K well. (C) 1999 American Institute of Physics. [S0021-8979(99)28808-1].