Direct observation of low energy nuclear spin excitations in HoCrO₃by high resolution neutron spectroscopy

Abstract

We have investigated low energy nuclear spin excitations in the strongly correlated electron compound HoCrO3. We observe clear inelastic peaks at E = 22.18 ± 0.04 μeV in both energy loss and gain sides. The energy of the inelastic peaks remains constant in the temperature range 1.5-40 K at which they are observed. The intensity of the inelastic peak increases at first with increasing temperature and then decreases at higher temperatures. The temperature dependence of the energy and intensity of the inelastic peaks is very unusual compared to that observed in other Nd, Co, V and also simple Ho compounds. Huge quasielastic scattering appears at higher temperatures presumably due to the fluctuating electronic moments of the Ho ions that get increasingly disordered at higher temperatures. The strong quasielastic scattering may also originate in the first Ho crystal-field excitations at about 1.5 meV.

Hyperfine and crystal field interactions in multiferroic HoCrO3

“…This reassures the validity of the large linear coefficient obtained by fitting the specific heat data at higher temperatures. From our earlier detailed report on the temperature dependence quasielastic scattering in HoCrO 3 [22] we found that the intensity decreases sharply below 40 K. Further the temperature dependence of ordered magnetic moment of Ho obtained from our recent neutron powder diffraction measurements [50], varies inversely as the temperature dependence of quasielastic scattering intensity and shows a sharp increase below 40 K. This confirms that the origin of quasielastic scattering is indeed fluctuating Ho moments which are short range in nature. A similar phenomenon was also observed in Ho 2 Ti 2 O 7 , the authors have interpreted it as being due to the fluctuating electronic moments of the Ho [35].…”

“…More details of this measurement is presented in reference [22]. Inelastic neutron scattering experiments were also carried out on the high-resolution time-of-flight spectrometer FOCUS at the Spallation Neutron Source SINQ at PSI, Villigen in Switzerland.…”

“…The inelastic peaks at both energy loss and energy gain sides are fitted by convoluting the instrument resolution function determined from vanadium with two delta functions for two inelastic peaks (magenta and green lines) plus one delta function for the elastic peak (blue line). The horizontal line is the flat background term [22]. (c) INS spectra collected on the instrument FOCUS, with neutrons of incident energy E i = 19.61 meV at temperature 1.5 K. Three well-resolved peaks at ε 2 , ε 3 and ε 4 are fitted using a Gaussian peak function.…”

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.…”

Atypical multiferroicity of HoCrO3 in bulk and film geometry

“…Thermal variation of w ZFC À1 is also plotted in the same Figure, which demonstrates that the plot deviates from Curie-Weiss (CW) behavior below B155 K followed by a sharp fall of w ZFC À1 with T N at 142 K, in accordance with the reported results. [24][25][26] The w ZFC and w FC recorded with 1 kOe in ZFC and FC protocols, respectively, are depicted in Fig. Neutron diffraction studies proposed an antiferromagnetic order of Cr 3+ ions below T N followed by the Ho 3+ order with a strong Ho-Cr hybridization.…”