arXiv:2001.05244v2 [cond-mat.str-el] 2 Jul 2020 Emergence of weak pyrochlore phase and signature of field induced spin ice ground state in Dy 2-x La x Zr 2 O 7 ; x = 0, 0.15, 0.3 Sheetal 1 , Anzar Ali 2 , Sarita Rajput 3 , Yogesh Singh 2 , T.Maitra 3 , and C.S. Yadav 1∗ 1 School of Basic Sciences, Indian Institute of Technology Mandi, Mandi-175005, (H.P.), India 2 Department of Physics, Indian Institute of Science Education and Research Mohali, Mohali-140306 , (Punjab), India and 3 Department of Physics, Indian Institute of Technology Roorkee, Roorkee-247667, (Uttrakhand), India The pyrochlore oxides Dy2Ti2O7 and Ho2Ti2 O7 are well studied spin ice systems and have shown the evidences of magnetic monopole excitations. Unlike these, Dy2Zr2O7 is reported to crystallize in a distorted fluorite structure. We present here the magnetic and heat capacity studies of La substituted Dy2Zr2O7. Our findings suggest the absence of spin ice state in Dy2Zr2O7 but the emergence of the magnetic field induced spin freezing near T ≈ 10 K in ac susceptibility measure- ments which is similar to Dy2Ti2 O7. The magnetic heat capacity of Dy2Zr2O7 shows a shift in the peak position from 1.2 K in zero field to higher temperatures in the magnetic field, with the corresponding decrease in the magnetic entropy. The low temperature magnetic entropy at 5 kOe field is Rln2 - (1/2)Rln(3/2) which is same as for the spin ice state. Substitution of non-magnetic, isovalent La 3+ for Dy 3+ gradually induces the structural change from highly disordered fluorite to weakly ordered pyrochlore phase. The La 3+ substituted compounds with less distorted pyrochlore phase show the spin freezing at lower field which strengthens further on the application of magnetic field. Our results suggest that the spin ice state can be stabilized in Dy2Zr2O7 either by slowing down of the spin dynamics or by strengthening the pyrochlore phase by suitable substitution in the system. I. INTRODUCTION Geometrically frustrated magnetic systems have been a subject of continuing research interest because of the re- alization of interesting quantum phases, non-trivial mag- netic ordering and excitations originating from the com- peting ferromagnetic (FM) and antiferromagnetic (AFM) interactions [1–6]. Of particular interest are the py- rochlore oxides: Dy 2 Ti 2 O 7 , Nd 2 Zr 2 O 7 and Ho 2 Ti 2 O 7 where the exotic magnetic and thermodynamic proper- ties have been observed [7–10] at low temperature. Py- rochlore oxide A 2 B 2 O 7 , (A is the trivalent rare-earth ion and B tetravalent transition metal ion) contains a net- work of corner-sharing tetrahedra where the magnetic rare-earth ions reside at the corners of tetrahedra and play a major role in deciding the magnetic behavior of these systems [11, 12]. In pyrochlores, the exotic mag- netic ground state is achieved by three competing inter- actions: AFM exchange interaction, FM dipolar inter- actions and crystal electric field (CEF), where the dom- inant effect of CEF forces the spin to point either di- rectly towards or away from the center of the tetrahedra and induces spin anisotropy in the system. For exam- ple, in Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 spin ice ground state is achieved by spins and their excitations are magnetic monopoles, Er 2 Ti 2 O 7 has the AFM ordering which is achieved through order-by-disorder mechanism and spin liquid ground state is observed in Tb 2 Ti 2 O 7 [13–16]. The computational studies on these systems have suggested the presence of spin ice state (two in-two out ordering) due to the dominance of FM dipolar interactions over the AFM exchange interactions which favors all-in-all-out or- dering. [17, 18] More recently Ramon et al. have shown Dy 2 Zr 2 O 7 to crystallize in defect-fluorite structure with lattice con- stant a = 5.238(2) ˚ A [19]. Unlike Dy 2 Ti 2 O 7 , Dy 2 Zr 2 O 7 shows the absence of spin ice state [20]. Although the specific heat and neutron scattering studies suggest very dynamic, short range, AFM spin-spin correlation below 10 K and the system remains disordered down to 40 mK with a significant value of magnetic susceptibility [19]. In Dy 2 Ti 2 O 7 , the spin state satisfy the two-in two- out ice rule and possess the Pauling’s residual entropy of (R/2)ln(3/2), which is absent in case of Dy 2 Zr 2 O 7 [19, 20]. However, similar to Dy 2 Ti 2 O 7 a correlation peak is present in Dy 2 Zr 2 O 7 around 2 K in the heat ca- pacity measurement [19]. These results indicate that the combined effect of Zr 4+ disorder and spin frustration at low temperature leads to the dynamic ground state of Dy 2 Zr 2 O 7 [19]. Here, we present the structural, magnetic and thermo- dynamic properties of Dy 2−x La x Zr 2 O 7 ; x = 0, 0.15, 0.3 based on dc magnetic susceptibility, ac magnetic suscep- tibility, isothermal magnetization and heat capacity mea- surements. It is observed that Dy 2 Zr 2 O 7 is a frustrated magnetic system which undergoes spin freezing transi- tion at T f ∼ 10 K in ac susceptibility measured in the presence of dc magnetic field of 5 kOe. This spin freezing transition is similar to the transition in Dy 2 Ti 2 O 7 at T = 16 K in zero dc field, which is lost due to large struc- tural disorder introduced by Zr atoms, and recovers on application of magnetic field. The partial substitution of non-magnetic La 3+ in place of magnetic Dy 3+ stabi- lizes the pyrochlore phase and spin-ice behavior is seen at lower fields. These results suggests that magnetic field can induce the spin-ice state in Dy 2 Zr 2 O 7 and La substi- tution can favor spin-ice formation at even lower fields.