Kim D, Revaz B, Zink B L, Hellman F, Rhyne J J, Mitchell J F
Department of Physics, University of California, San Diego, La Jolla 92093, USA.
Phys Rev Lett. 2002 Nov 25;89(22):227202. doi: 10.1103/PhysRevLett.89.227202. Epub 2002 Nov 7.
We report on the doping dependence of the order of the ferromagnetic metal to paramagnetic insulator phase transition in La1-xCaxMnO3. At x=0.33, magnetization and specific heat data show a first order transition, with an entropy change (2.3 J/mol K) accounted for by both volume expansion and the discontinuity of M approximately 1.7mu(B) via the Clausius-Clapeyron equation. At x=0.4, the data show a continuous transition with tricritical point exponents alpha=0.48+/-0.06, beta=0.25+/-0.03, gamma=1.03+/-0.05, and delta=5.0+/-0.8. This tricritical point separates first- (x<0.4) from second-order (x>0.4) transitions.
我们报道了La1-xCaxMnO3中铁磁金属到顺磁绝缘体相变顺序的掺杂依赖性。在x = 0.33时，磁化强度和比热数据显示为一级相变，通过克劳修斯-克拉珀龙方程，熵变（2.3 J/mol K）由体积膨胀和M的不连续性（约1.7μB）共同构成。在x = 0.4时，数据显示为具有三临界点指数α = 0.48±0.06、β = 0.25±0.03、γ = 1.03±0.05和δ = 5.0±0.8的连续相变。这个三临界点将一级相变（x < 0.4）与二级相变（x > 0.4）区分开来。
