Antiferromagnetic short-range order and cluster spin-glass state in diluted spinel ZnTiCoO₄

Abstract

The nature of magnetism in the doubly-diluted spinel ZnTiCoO4 is reported here employing the temperature and magnetic field dependence of dc- and ac-susceptibilities, and heat capacity (CP) measurements. The antiferromagnetic Néel temperature (TN~13.8 K) is determined from the peak in the ∂(χT)/∂T vs. T plot and the Power law yields the spin-glass freezing temperature Tg ~ 12.9 K with critical exponent zν ~ 11.75. Since the magnitudes of t o and zν depend on the magnitude of Tg, a procedure is developed to find the optimum value of Tg = 12.9 K. A similar procedure is used to determine the optimum T0 = 10.9 K in the Vogel-Fulcher law yielding Ea/kB = 95 K, and t 0 = 1.6 ×10-13 sec. It is argued that the comparatively large magnitude of the Mydosh parameter Ω = 0.024 and Ea/(kBT0)=8.7(>>1) suggests cluster-spin-glass state in ZnTiCoO4 below Tg. In the CP vs T data from 1.9K to 50K, the observation of only a broad peak near 20K and absence of λ-type anomaly near TN or Tg combined with the reduced value of change in magnetic entropy from 50K to 1.9K suggests the presence of only short-range ordering in the system, consistent with spin-glass state. The field dependence of Tg shows slight departure from the non-mean-field Almeida-Thouless line. Strong temperature dependence of magnetic viscosity S and coercivity HC without exchange bias, both tending to zero on approach to Tg from below, further support the spin-glass state which results from magnetic dilution driven by Zn2+ and Ti4+ ions leading to magnetic frustration. Magnetic phase diagram in the H-T plane is established using the high-field magnetization data M(H,T) for T < TN which reveals rapid decrease of Tg with increase in H whereas decrease in TN with increase in H is weaker, typical of antiferromagnetic systems.

Spin-liquid state with precursor ferromagnetic clusters interacting antiferromagnetically in frustrated glassy tetragonal spinel Zn0.8Cu0.2FeMnO4

“…To investigate the long-range vs. shortrange magnetic ordering in ZCFMO, the thermal variation of its heat capacity C p was vs. T. Although the magnitude of −∆C p is comparatively small, it shows that applied H suppresses C p with a peak in its magnitudes around 80 K. This variation is likely due to coupling of the FM clusters to the applied H. More importantly, in the C p (0) vs. T data, a λ-type anomaly characteristic of LRO is not observed as often reported for second order magnetic transitions [39,52]. However, lattice contribution to C p must be first subtracted out from the measured C p before any magnetic contribution to C p can be ruled out.…”

“…Since k B T 0 /E a = 36.8/195.1 ≃ 0.19 is much less than unity, it shows that inter-cluster interaction is weaker than the energy barrier between clusters, leading to the cluster glass state without long range magnetic order. The magnitude of τ 0 and zν are characteristic of SGs, although it is now realized that their magnitudes cannot be used to distinguish between cluster and canonical SGs [31,39]. In summary, the magnitude of Ω = 0.0246, combined with k B T 0 /E a ≪ 1 establishes this system as a cluster SG.…”

“…In a recent paper from our group [39], we have presented a procedure to determine optimum magnitudes of T 0 and T SG using an adjusted R 2 method, noting that adjusted R 2 = 1 for optimum values. In figure 6, we show the results of this procedure for the peak near 47 K by plotting adjusted R 2 vs. different choices of T SG and T 0 and determining the corresponding magnitudes of τ 0 , zν and E a /k B .…”

Slow spin dynamics of cluster spin-glass spinel Zn(Fe 1−x Ru x )2O4: role of Jahn–Teller active spin-1/2 Cu2+ ions at B-sites

“…An additional weak hump noticed below T FiM at ∼11.2 K in figure 3(b) may be originating due to the progressive freezing of spin clusters in locally ordered states similar to the systems which exhibit Gabay-Toulouse type mixed phases [76][77][78][79][80]. Usually, such transitions are not so prominent under low-fields (H DC ⩽ 1 kOe) [81,82]. Since these magnitudes are sensitive to the strength of external applied field, such field (H DC ) variation by virtue of both temperature and frequency dependent analysis of ac-(and dc-) magnetic susceptibility are discussed below in a detailed way.…”

Reentrant canonical spin-glass dynamics and tunable field-induced transitions in (GeMn)Co2O4 Kagomé lattice

“…However, the magnitudes of Φ and T F (0) obtained from the peak transitions of χ ′ (T) and χ ′′ (T) result in slight deviations from the ideal mean-field model (Φ = 2.8 and 4.1 obtained from real and imaginary components, respectively). Usually, departure of Φ from its ideal value of 3 is commonly noticed in several isostructural systems like ZnTiCoO 4 , Co 2 RuO 4 and (Mn x Ti 1−x ) Co 2 O 4 [24,49,50]. It is interesting to note that there is a broad hump across 23 K (T * ) close to the structural phase transition usually noticed in GCO (T D ∼ 16 K), however, in the present case this transition occurs at slightly higher temperatures due to the incorporation of Mn in the Kagomé lattice [9].…”