Pressure-Induced Ferromagnetic to Nonmagnetic Transition and the Enhancement of Ferromagnetic Interaction in the Thiazyl-Based Organic Ferromagnet γ-BBDTA·GaCl4

A thiazyl-based ferromagnet, the γ-phase of BBDTA (i.e., benzo[1,2- d :4,5- d \u27]bis[1,3,2]dithiazole)·GaCl 4 , has a high ferromagnetic ordering temperature of 7.0 K in organic radical ferromagnets. In this system, pressurization generated more compact molecular packing, resulting in that the ferromagnetic state at P = 16.2 kbar is stabilized over a temperature range of more than twice of the initial range. However, the saturation magnetic moment was reduced with increasing pressure, decreasing to about 12% of the initial value even at the low pressure level of P = 1.0 kbar. This suggests that the ferromagnetic molecular packing of the monoclinic γ-phase is easily transformed into that of the diamagnetic phase. Powder X-ray diffraction experiments revealed that the diamagnetic non-monoclinic (α- or β-) phase became stable instead of the monoclinic γ-phase across the pressure of 2.5–5.8 kbar. The increase in the temperature of onset of ferromagnetic state occurs in the surviving ferromagnetic domain surrounded by the diamagnetic domains

Volume shrinkage dependence of ferromagnetic moment in lanthanide ferromagnets gadolinium, terbium, dysprosium, and holmium

The Gd–Ho series of lanthanide ferromagnets, which includes gadolinium (Gd), terbium (Tb), dysprosium (Dy), and holmium (Ho), undergoes similar structural transitions, e.g., the hcp→Sm-type→dhcp→fcc transitions, under pressure. Through high-field DC magnetic measurements and structural analyses, we found that the ferromagnetic moments disappeared at a specified critical pressure, which resulted in volume shrinkage of 16.7±1.7% for each ferromagnet. The results of the present study suggest that the disappearance of the ferromagnetic moments of Gd–Ho under pressure could be understood within the framework of a band picture related to volume shrinkage