Hyperfine and crystal field interactions in multiferroic HoCrO₃

Abstract

Abstract. We report a comprehensive specific heat and inelastic neutron scattering study to explore the possible origin of multiferroicity in HoCrO 3 . We have performed specific heat measurements in the temperature range 100 mK-290 K and inelastic neutron scattering measurements were performed in the temperature range 1.5-200 K. From the specific heat data we determined hyperfine splitting at 22.5(2) µeV and crystal field transitions at 1.379(5) meV, 10.37(4) meV, 15.49(9) meV and 23.44(9) meV, indicating the existence of strong hyperfine and crystal field interactions in HoCrO 3 . Further, an effective hyperfine field is determined to be 600(3) T. The quasielastic scattering observed in the inelastic scattering data and a large linear term γ = 6.3(8) mJmol −1 K −2 in the specific heat is attributed to the presence of short range exchange interactions, which is understood to be contributing to the observed ferroelectricity. Further the nuclear and magnetic entropies were computed to be, ∼17.2 Jmol −1 K −1 and ∼34 Jmol −1 K −1 , respectively. The entropy values are in excellent agreement with the limiting theoretical values. An anomaly is observed in peak position of the temperature dependent crystal field spectra around 60 K, at the same temperature an anomaly in the pyroelectric current is reported. From this we could elucidate a direct correlation between the crystal electric field excitations of Ho 3+ and ferroelectricity in HoCrO 3 . Our present study along with recent reports confirm that HoCrO 3 , and RCrO 3 (R = Rare earth) in general, possess more than one driving force for the ferroelectricity and multiferroicity.

Magnetic frustration in a metallic fcc lattice

“…It should be noted that the literature values for a and p cannot describe our data satisfactorily [24]. In contrast to HoInCu 4 where C mag peaks well below 200 mK, all other Ho compounds reported in the literature show a larger energy splitting of the nuclear moments, i.e., a nuclear Schottky anomaly at much higher temperature [24][25][26][27][28]. The reduced temperature scale of the Schottky anomaly in HoInCu 4 is attributed to the reduced internal magnetic fields in this compound.…”

Quasielastic and low-energy inelastic neutron scattering study of HoCrO3by high resolution time-of-flight neutron spectroscopy

“…1 and 2. The two lowest crystal field states of the free ion term 5 I 8 are singlets, split by an energy of about D = 0.5 meV in paramagnetic state of HoCrO 3 , are well below the next excited crystal field state [25,26,34,36] which has an energy of 10 meV and is much higher than D = 0.5 meV. Thus the two lowest energy singlet states can be treated as an accidental ground doublet or just doublet for brevity.…”

Spectroscopic analysis of vibronic relaxation pathways in molecular spin qubit $[$Ho(W$_5$O$_{18}$)$_2]^{9-}$: sparse spectra are key

“…f -block elements like Ho 3+ also display crystal field levels in the far infrared. [31][32][33] The exact position of the f -manifold levels varies significantly depending upon the details of the crystal field environment. 13,34,35 Previous authors located the M J = ± 3 and ± 5 levels in 2 in orange and help to define a lower limit to the crystal field manifold.…”