Parimagnetism in HoCo₂and TmCo₂

Abstract

X-ray magnetic circular dichroism (XMCD), longitudinal (χac) and transverse (TS) ac magnetic susceptibility have been measured in the RCo2 series (R = Ho, and Tm) as a function of temperature and applied magnetic field. We show that parimagnetism is a general behavior among the RCo2 ferrimagnetic series (R being a heavy rare-earth ion). XMCD results supply evidence of the presence of two compensation temperatures above Tc, defining two different parimagnetic configurations, which is a fully unexpected result. The inverse χ'ac curve exhibits a small anomaly which vanishes under low applied magnetic fields. The combination of TS and XMCD measurements allows one to depict new magnetic phase diagrams for these compounds of the RCo2 series. A new scenario allowing one to understand the observed phenomenology as a Griffiths phase-like behavior is proposed, where the amorphous RCo2 represents the undiluted system case.

Magnetism in TmCo2

“…We suppose that these discrepancies come from dierent quality of the measured samples. Based on the characterization of our sample by XRD and EDX, we trust in a good quality of our sample showing better purity in comparison with our samples from the RCo 2 family, showing more consistent results with literature [2,6,7]. The position of anomaly denoted by T f is in the agreement with the position of ipping temperature published in [7] obtained from the XMCD measurement.…”

Balancing structural distortions via competing 4f and itinerant interactions: a case of polymorphism in magnetocaloric HoCo2

“…21,23 Two clearly defined peaks were observed in ac susceptibility, w ac (T), of HoCo 2 at T C and at T SR , and two additional minor anomalies (at B40 K and near T SR ) are present as well. 24 Bonilla et al 25 observed two major anomalies at T C and T SR plus a weak anomaly in the paramagnetic region at 126 K. Apparently, the w ac (T) data are sample dependent even though the singlephase composition of HoCo 2 alloys is claimed in nearly all published studies.…”

Lattice distortion in TmCo2: A poly- and single-crystal study

“…It follows that the single-crystal doesn't exhibit the first order phase transition, which is crucial for the existence of the magnetic Co-sublattice. This contradiction may be clarified by the discrepancies appearing in the literature [6,[11][12][13][14][15][16][17][18][19].…”

“…In this reference the critical molecular field is related to the metamagnetic transition in the analogue YCo 2 . This fact leads to discrepancies in the literature, where one can find results with a magnetic [6,[15][16][17] as well as non-magnetic cobalt sublattice [11-14, 18, 19]. These two cases are ascribed to the observation of a FOMPT [20] or SOMPT (second order magnetic phase transition) respectively.…”