PHYSICAL REVIEW B 100, 184424 (2019) Study of phase separation phenomena in half-doped manganites with isovalent substitution of rare-earth cations on example of Sm 0.32 Pr 0.18 Sr 0.5 MnO 3 A. I. Kurbakov , V. A. Ryzhov , V. V. Runov, E. O. Bykov, I. I. Larionov, and V. V. Deriglazov * Petersburg Nuclear Physics Institute named by B. P. Konstantinov of National Research Centre “Kurchatov Institute”, 1 Orlova roscha, Gatchina, Leningrad Region 188300, Russia C. Martin and A. Maignan CRISMAT, Normandie Université, ENSICAEN, UNICAEN, CNRS, CRISMAT, 14000 Caen, France (Received 10 September 2019; revised manuscript received 14 November 2019; published 27 November 2019) The effect of isovalent substitution of rare-earth cations on the phase separation in half-doped manganites was studied on the example of Sm 0.32 Pr 0.18 Sr 0.5 MnO 3 by high-resolution neutron powder diffraction, neutron beam depolarization, second-harmonic magnetic response, and magnetization and resistivity measurements from 4 K up to room temperature and higher. A structural phase transition from the orthorhombic Pbnm phase to a mixture of Pbnm and monoclinic P2 1 /m phases was observed upon cooling. The magnetic ground state was found to be phase-separated into three magnetic phases emerging at different temperatures, viz., ferromagnetic (FM) and antiferromagnetic A and charge-ordered CE types. FM clusters arise far above room temperature in the orthorhombic phase and coalesce upon cooling to produce the long-range FM order below 250 K and to arrive at the percolative FM phase below 120 K. The A- and CE-type orders form in the monoclinic phase at the temperatures 200 K and 120 K, respectively. The Sm/Pr isovalent substitution qualitatively changes the phase separation and significantly increases its temperature range compared to the parent compounds. The results obtained give us knowledge of phase separation occurring in systems with strong electron correlations and extend opportunities for fine-tuning of their properties. DOI: 10.1103/PhysRevB.100.184424 I. INTRODUCTION Phase separation (PS) is a generic feature of rare- earth manganites doped with alkali-earth ions (R 1−x A x MnO 3 ) underlying their remarkable magnetic, transport, magne- tocaloric, and other properties applicable in technology [1]. This tendency is especially pronounced in the vicinity of phase boundaries, both in temperature and doping, where the system becomes more unstable to PS. For certain doping levels x, magnetic and structural phases and their alternation with temperature may considerably differ depending on the particular R and A cations. For instance, in the region close to x = 0.5, Ca-based Sm, Pr, Nd, and La manganites exhibit antiferromagnetic (AF) charge-ordered-type (CE) insulating ground states whereas these manganites (except, maybe, with Nd [2] and Sm [3]) half-doped with Sr ions possess the more conductive AF A-type structure [2,4,5]. Generally, x = 0.5 is a particular doping level in the manganite phase diagrams sep- arating mainly FM underdoped (x < 0.5) and AF overdoped (x > 0.5) areas with different crystal structures. Changing the chemical pressure due to different ionic radii of Ca and Sr ions modifies local structural parameters such as the Mn-O bond distances and Mn-O-Mn bond angles, which, in turn, essentially determine magnetic and transport properties via variation of electron hopping integrals. Thus, a partial sub- stitution of Ca 2+ for Sr 2+ or some other divalent cation with * deriglazov_vv@pnpi.nrcki.ru the continuous shift of the average ionic radius of the A cation, the Mn 3+ /Mn 4+ ratio being fixed, enables wide-range gradual variation of the manganite characteristics and their fine-tuning for particular application needs [6]. Herewith, such isovalent substitution (IS) can be accompanied by specific PS as shown, e.g., for Pr 0.5 Ca 0.2 Sr 0.3 MnO 3 [7]. The IS approach adds and is alternative to the conventional A-cation doping by changing the Mn 3+ /Mn 4+ ratio. As IS implies a fixed concentration of charge carriers, it affects the manganite properties more subtly, only via variation of geometrical parameters, viz., the average cationic radius and the radius variance. Besides, in the vicinity of x = 0.5, it is reasonable to expect coexistence of several (more than two) magnetic phases in the state with structural PS. A partial substitution of trivalent R-cations provides even wider possibilities as the row of lanthanides is much longer than the alkali-earth one. Among numerous examples is the manganite La 0.15 Sm 0.85 MnO 3.1 , where coexistence of nanoscale superconductivity and a fluctuating AF spin-liquid state was suggested [8]. The IS of rare-earth ions provides also an additional degree of freedom for optimizing the mag- netocaloric effect. Doping La 0.7 Ca 0.3 MnO 3 with Nd 3+ ions was shown to increase the magnetic entropy gain reaching the maximum in La 0.5 Nd 0.2 Ca 0.3 MnO 3 [9]. Similarly, the magnetocaloric effect in Sm 0.55−y Pr y Sr 0.45 MnO 3 was found to be optimized at y = 0.1 with the outlook of employing this compound in magnetic refrigerators [10]. The systematic rare-earth IS can be used as a means for deeper insight into the physics of doping and 2469-9950/2019/100(18)/184424(11) 184424-1 ©2019 American Physical Society