Microscopic evidence for magnetic-phase coexistence in the intermetallic compound ${\mathrm{Nd}}_7{\mathrm{Rh}}_3$

The intermetallic compound ${\mathrm{Nd}}_7{\mathrm{Rh}}_3$, which shows two magnetic transitions, one at 32 K and another around 16 K, has been known to exhibit a magnetic-field induced first-order magnetic phase transition (FOPT) at low temperatures. Using neutron diffraction we tracked the evolution of the magnetic features as a function of temperature and external magnetic field across the two transition temperatures. We provide evidence for the existence of both antiferromagnetism and ferromagnetism below 20 K. Notably the results reveal concrete evidence for the partial persistence of the high-field magnetic state at 2 K after cycling through the magnetic-field-induced magnetic transition, thereby offering microscopic evidence for magnetic coexistence phenomenon in this intermetallic compound.

Figure 1

Magnetic susceptibility of ${\mathrm{Nd}}_7{\mathrm{Rh}}_3$ in an applied field of 100 Oe measured in zero-field-cooled (ZFC) and field-cooled (FC) state of the sample. The two magnetic transitions at 32 and 16 K are clearly seen from the figure.

Figure 2

Thermodiffractogram for ${\mathrm{Nd}}_7{\mathrm{Rh}}_3$ measured in the zero applied dc field is shown here. The inset exhibits the expanded region of the strong antiferromagnetic peak observed at a $Q$ value (in 2θ) of 0.1 Å${}^{-1}$ (${2.3}^o$).

Figure 3

(a)–(c) Rietveld refinement of ND patterns recorded in zero field at $T$ = 50, 20, and 2 K respectively, are shown here. The pattern at 2 K is refined using a structural phase (indicated by the first row of vertical tick marks), AFM phase (second row), and the FM phase (third row). Among the magnetic phases, at 20 K only the AFM phase exists, whereas at 50 K only the structural (nuclear) phase is refined.

Figure 4

(a) Magnetic structure of the antiferromagnetic phase of ${\mathrm{Nd}}_7{\mathrm{Rh}}_3$ with Nd (Rh) atoms as black (red) balls shown in a slightly oblique view along the $c$ axis. The sine-wave modulated moments are green (blue) for the Nd1 (Nd2) $6c$ sites and red for the Nd3 $2a$ site. (b) Magnetic structure of the ferromagnetic phase.

Figure 5

The figure shows a profile of the variation of the integrated intensity of the (0 0 0) magnetic peak qualitatively as a function of temperature to highlight the existence of a broad peak around 20 K. The same figure also shows the influence of cooling in the presence of external magnetic field (11 kOe) on the magnetic peak intensity. Both curves are obtained from measurements done in zero field while warming.

Figure 6

(a) Thermal variation of unit cell volume calculated from ND patterns recorded in zero field is shown here. The bottom panel highlights the variation in the c/a ratio. (b) The figure exhibits the site moments for Nd1 (=Nd2) and Nd3. The top and bottom panels indicate AFM and FM moments.

Figure 7

(a) ND patterns measured at 2 K in three conditions after zero field cooling the sample. In the first step ND patterns were measured in zero field, and then in 11 kOe, and finally in zero field immediately after removing the field. (b) ND patterns measured at 20 K again, in three conditions, that in $H$ = 0, 11 kOe, and again in 0, immediately after removing the field. (c) and (d) Changes in the cell volume under the influence of the magnetic field at 2 and 20 K, respectively.

Figure 8

ND experiments were carried out on ${\mathrm{Nd}}_7{\mathrm{Rh}}_3$ after cooling the sample in one field ($H$ = 0 or 30 kOe), and then measuring ND patterns in another field ($H$ = 0 or 2 kOe) following the CHUF (cooling and heating in unequal fields) protocol.