Origin of negative magnetization phenomena in (Tm1−xMnx)Mn

Abstract

Tm 1−x Mn x )MnO 3 solid solutions were synthesized at a high pressure of 6 GPa and a high temperature of about 1570-1670 K for 2 h for x = 0, 0.1, 0.2, and 0.3. Magnetic, dielectric, and neutron diffraction measurements revealed that the introduction of magnetic Mn 2+ cations into the A site leads to an incommensurate spin structure for x = 0.1 and to a ferrimagnetic structure for x 0.2. Commensurate magnetic structures have a much larger correlation length (∼400 nm for x = 0, ∼600 nm for x = 0.3) than the incommensurate magnetic structure (∼12 nm for x = 0.1). The presence of Tm 3+ and Mn 2+ (with different sizes) at the A site causes significant microstrain effects along the a direction which are absent for x = 0 and get stronger with increasing x. Magnetic ordering occurs at the Néel temperature T N = 37 K (x = 0.1) and at the ferrimagnetic Curie temperatures T C = 75 K (x = 0.2) and T C = 104 K (x = 0.3). Ordering of magnetic Mn moments triggers short-range order (for x = 0.1) and long-range order (for x 0.2) of the Tm 3+ cations at the same temperaturean unusual situation in perovskite materials with a simple GdFeO 3 -type Pnma structure. For x = 0.1, long-range IC magnetic order [with propagation vector k = (k 0 , 0, 0) and k 0 ≈ 0.40] of Mn 3+ and Mn 4+ cations at the B site coexists with short-range order of Tm 3+ and Mn 2+ moments at the A site. Short-range order is induced at the Néel temperature T N = 37 K, increases towards an additional specific heat anomaly at T = 4 K, and remains at lower temperature. The ferrimagnetic structure [with propagation vector k = (0, 0, 0)] consists of ferromagnetically ordered Mn 3+ and Mn 4+ cations at the B site which are coupled antiferromagnetically with ordered Mn 2+ moments at the A site. Tm 3+ moments adopt a zigzag magnetic structure which contains a macroscopic ferromagnetic moment that aligns with the direction of the ordered Mn 2+ moments. Towards low temperature, the ordered Tm 3+ moments strongly increase and overcome the saturated magnetic Mn moments at the B site, and this behavior results in the observation of magnetization reversal or negative magnetization phenomena with a compensation temperature of about 15 K at small magnetic fields in the x = 0.2 and 0.3 samples. This is a classical mechanism of the magnetization reversal effects for ferrimagnets. at T N,R = 2−10 K [3]. A more complex picture takes place in RMnO 3 manganites, where there are two magnetic transitions associated with the Mn 3+ at the B site (for R = Gd-Lu and Y) [4], and R 3+ cations order at relatively higher temperatures in comparison with RFeO 3 and RCrO 3 , for example, T N,Mn = 73 K and T N,Nd = 15 K in NdMnO 3 [5], and T N,Mn = 47.5 K and T N,Ho ≈ 20 K in HoMnO 3 [6]. In o-TmMnO 3 , a parent compound of this study [7], an incommensurate (IC) spin structure at the Mn site (B site) appears below T N1,Mn = 42 K and locks into a commensurate noncollinear E -type structure below T N2,Mn = 30−32 K with the appearance of spin-induced ferroelectricity. Tm 3+ cations at the A site spo...

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

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“…The magnetization of EuHoCuSe 3 below the Néel point looks significantly different, and its value is negative at temperatures from 4.2 to 4.8 K. This recently attracted increased interest for possible practical applications [81,82]. Several mechanisms of this phenomenon are considered: negative exchange coupling among ferromagnetic sublattices, negative exchange coupling among canted antiferromagnetic sublattices, negative exchange coupling among ferromagnetic/canted antiferromagnetic and paramagnetic sublattices, imbalance of spin and orbital moments, interfacial exchange coupling between ferromagnetic and antiferromagnetic phases [81].…”

Temperature evolution of 3d- and 4f-electron magnetic ordering in the ferrimagnetic Mn self-doped perovskite (Yb0.667Mn0.333)MnO3

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“…We have recently found that Mn self-doping of RMnO 3 perovskites, (R 1-x Mn x )MnO 3 , can significantly modify their magnetic properties and magnetic phase transition sequences [17][18][19]. Even small doping levels (x = 0.05-0.1) prevent the appearance of the E-type AFM phase but keep the IC AFM phase [18,19]-this effect is somewhat similar to the effects of oxygen nonstoichiometry on RMnO 3 perovskites. Larger doping levels change the ground state to a ferrimagnetic (FiM) state, trigger long-range magnetic ordering of R 3+ /Mn 2+ cations at significantly higher temperatures than in parent RMnO 3 perovskites, and can result in a magnetization reversal phenomena [19].…”

Cycloidal spiral magnetic structures in the spin-chain compounds BaRFeO4 ( R=Yb and Tm): Ordered Yb versus partly ordered Tm

“…Information about magnetic structures (such as magnetic space group, propagation vectors, magnitude, and direction of spins at each site and their evolution with temperature) is essential for correct understanding and interpretation of macroscopic magnetic and sometimes dielectric/ferroelectric properties of materials [1]. For example, macroscopic negative magnetization phenomena, when magnetization decreases with decreasing temperature and becomes negative, are often connected to the presence of two (or several) magnetic sublattices, coupled antiferromagnetically and having nonequal ordered moments, and their different evolution with temperature [2][3][4]. In type-II multiferroics, macroscopic ferroelectric polarization develops in otherwise centrosymmetric materials due to breaking the inversion symmetry by a magnetic order [1,5,6].…”