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We report anomalous magnetic properties in high DC magnetic fields H up to 16 T on an underdoped PrBa2Cu3O6.44 insulating ceramic sample of cuprate family. Significant magnetic-field effects are revealed in the derivative dM(T)/dT of the magnetization M(T) versus T using two sets of values of H selected in the range of 2.5-9.5 T. Anomalies are observed in the region of Tcr ~ 4.5 K, T2 ~ 6.5 K and TN = 9 K, which are respectively the well-known low-critical point, the spin reorientation phase transition temperature, and the Néel temperature of the antiferromagnetic (AFM) ordering of the Pr3+ sublattice [1]. Using Arrott plot analysis, we identified at 1.35 K weak field-induced phase transitions at two critical fields, Hcr1 ~ 3.3 T and Hcr2 ~ 7.5 T, whose associated transition lines appear temperature-independent as T increases up to T2, and seem to vanish in the vicinity of TN. Between TN and 20 K, the curves of the derivative dM(H)/dH of the magnetization M(H) versus H show a slight increase when H is taken in the low-field range of 0.7 T < HS < 1.2 T. The field HS being the specific field above which the weak ferromagnetic (WFM) part settles in the Pr AFM regime as well as in the AFM state of the Cu(2) spins which takes place in the region of room temperature. As T decreases, HS increases monotonically, while dM(H)/dH exhibits a high-speed increase below Tcr. The M(H) curves obtained with a high accuracy, show obviously a linear field dependence in the range of HS-Hcr1, so, they may be represented by the equation MS(T) + χd(T)H. The spontaneous magnetization MS(T) and the differential magnetic susceptibility χd(T) are obtained by extrapolation to zero-field from the linear part of the M(H) curves in the low-field range (HS < H < 2 T). MS(T) decreases as the inverse of T, like for paramagnetic systems with a shape change when crossing TN and survives above TN. Whereas χd(T) has a behavior practically analogous to that of AFM materials and shows a shape change when crossing Tcr, T2, and TN. The M(H) - χd(T)H versus H curves present a metamagnetic-like field-induced transition at a threshold field Ht for H lower than 0.15 T. These anomalous features observed at low temperatures and surviving above TN, are taken as evidence for an additional weak ferromagnetic-like component. The results are compared with previous neutron-scattering study [2] and discussed in terms of the significant role of the Pr-Cu(2) coupling which appear to continue well above TN.
[1] M. Lahoubi, Physica B 536 (2018) 12.
[2] A. T. Boothroyd et al., phys. Rev. Lett., 78 (1997) 130.
| Submitters Country | Algeria |
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