Study of the low-field irreversibility line in the transverse component spin-glass phase of the amorphous Fe90Zr10 alloy

Amorphous FexZr100-x alloys display a complex magnetic phase diagram, particularly in the range 89% less than or similar to x less than or similar to 93% in which the phase transition from the paramagnetic to a soft ferromagnetic (FM) state at a critical temperature T-c precedes a second transition at T-xy < T-c to a transverse spin-glass (SG) phase, with frozen spin components transverse to the magnetization. The softness of the FM phase and the coexistence of FM and SG orderings complicate exploring the low-temperature and low-field critical properties of the glassy transition. Here we study the irreversibility Almeida-Thouless (AT) line that marks the onset of the transverse SG phase in the Fe90Zr10 alloy in the low-field regime up to H= 60 Oe. While ZFC measurements give rise to an AT exponent phi= 4.6, similar to that of another amorphous FM compound with random local anisotropy, the induction of magnetic shiftings upon cooling the sample in a large field, - 85 kOe, displaces down the AT line and separates it into two distinct regimes: one also with phi= 4.6 for Habove 20 Oe, nearly corresponding to the typical field to flip the remanent magnetization, and a new second regime at lowerH, with field-induced remanent clusters and exponent phi= 3.6 that approaches the mean-field value phi= 3. Our findings are discussed on the light of the results from a random nonuniform anisotropy model with FM exchange interactions, which also reported the existence of a two-regimes scenario in the AT line with similar exponents.