Kim Jae Wook, Haam S Y, Oh Y S, Park S, Cheong S-W, Sharma P A, Jaime M, Harrison N, Han Jung Hoon, Jeon Gun-Sang, Coleman P, Kim Kee Hoon
Center for Strongly Correlated Materials Research and Frontier Physics Research Division, Department of Physics and Astronomy, Seoul National University, Seoul 151-742, South Korea.
Proc Natl Acad Sci U S A. 2009 Sep 15;106(37):15573-6. doi: 10.1073/pnas.0907589106. Epub 2009 Aug 26.
The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a "metaelectric" critical end point, has been rarely studied. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field (H) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn(2)O(5), in which the electric polarization (P) switches polarity along with a concomitant Mn spin-flop transition at a critical magnetic field H(c). The simultaneous metaelectric and spin-flop transitions become sharper upon cooling but remain a continuous cross-over even down to 0.5 K. Near the P = 0 line realized at mu(0)H(c) approximately 18 T below 20 K, the dielectric constant (epsilon) increases significantly over wide field and temperature (T) ranges. Furthermore, a characteristic power-law behavior is found in the P(H) and epsilon(H) curves at T = 0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn(2)O(5) near zero temperature.
对被称为变磁转变的随磁场变化的磁化强度突然增加的研究，在巡游电子系统中开辟了一条丰富的新物理脉络，包括发现具有显著形成新型有序态倾向的量子临界端点。然而，变磁临界端点的电类似物，即“元电”临界端点，却很少被研究。磁性和铁电性相互交叉耦合的多铁性材料，是以磁场（H）作为调谐参数来探索这种新可能性的理想候选材料。在此，我们报告在多铁性材料BiMn₂O₅中发现了磁场诱导的元电转变，其中在临界磁场H(c)下，极化强度（P）随Mn自旋翻转转变而改变极性。随着冷却，同时发生的元电转变和自旋翻转转变变得更加尖锐，但即使在低至0.5 K时仍保持连续的转变。在20 K以下，在μ₀H(c)≈18 T时实现的P = 0线附近，介电常数（ε）在很宽的磁场和温度（T）范围内显著增加。此外，在T = 0.66 K时，P(H)和ε(H)曲线中发现了特征幂律行为。这些发现表明，在接近零温度的BiMn₂O₅中实现了磁场诱导的元电临界端点。
