Superconducting and normal state properties of ErRh4B4 and LuRh4B4

Abstract

Detailed heat capacity measurements of the ternary compounds ErRh4B~ and LuRh,d34 have been performed between 0.5 and 36 K and in magnetic fields up to 4 kG, yieMing new information on crystal fieM effects in these materials and on the influence of externally applied magnetic fields on the coupled superconducting-ferromagnetic reentrant transition in ErRh4B4. Static magnetic susceptibility data on LuRh4B4 are presented which allow qualitative conclusions to be drawn regarding the magnitude of exchange enhancement and orbital paramagnetic effects in the RURh4B~ compounds. The electrical resistivity of ErRh4B4 has also been determined between 4 K and room temperature.

Magnetic phase diagram and crystal fields of superconducting ErNi2B2C

“…Such a decrease in jump height for magnetic superconductors compared to their nonmagnetic allomorphs is not uncommon and has been observed for e.g. ErRh,~B4 [15]. Obviously, although the magnetism is not affecting superconductivity dramatically regarding transition temperatures, it does have an influence on the distribution of the superconducting entropy and the specific heat.…”

Observation of the coexistence of superconductivity and long-range magnetic order in TmRh4B4

“…4, emphasize the upturn at low temperatures and reveal a Schottky anomaly that peaks at approximately 20 K. These data are in good agreement with those of Smith et al ~~ and indicate that the magnitude of the crystalline electric field (CEF) splitting of the Tm 3+ J = 6 Hund's rule multiplet in this compound is comparable to that of the Er 3 § J = 15/2 multiplet in ErRh4B4. 15 The magnetic entropy AS between 0.5 and 4 K has a value of AS = 0.62R, nearly R In 2, implying that if the behavior of the heat capacity below 0.5 K were known, the magnetic entropy AS associated with the low-temperature ordering might be R In 3 or R In 4. It is thus likely that a low-lying CEF magnetic doublet state is at least partially responsible for the magnetic order below 0.5 K. An ad hoc CEF level scheme which successfully, although nonuniquely, fits the AC data is shown in Fig.…”

“…The considerable influence of external magnetic fields on the hightemperature tails of C (Ref. 15) and a (Ref. 12) for ErRh4B4 and o~ for TmRh4B4 suggests that part of the observed anomalies may have to be associated with Schottky anomalies arising from the near degeneracy of the 4f-electron energy levels of the crystal-field-split Hund's-rule ground-state multiplets.…”

Ferromagnetism in the RERh4B4 compounds

“…5 is the magnetic heat capacity AC divided by the molar gas constant R of each of these compounds derived by subtracting the normal state LuRh4B4 heat capacity from the total heat capacity in a manner previously described. 6 The magnetic heat capacity of HoRh4B4 (Fig. 4d) has a rapid increase below 2 K which has been attributed to a nuclear Schottky anomaly due to the lifting of the eight-fold degeneracy of the nuclear I = 7/2 levels by the effective magnetic field of the ordered Ho 3 § magnetic moments below TM.…”