First-order Magnetic Transition Research Articles

Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films.

High-quality Mn2-xCrxSb (x = 0.01, 0.04, and 0.1) epitaxial thin films were grown on SrTiO3 (STO) (001) single-crystal substrates using molecular beam epitaxy. Magnetotransport and magnetic measurements reveal that the x = 0.01 sample undergoes a quasi-ferrimagnetic (I) [Q-FIM(I)]-to-ferrimagnetic (II) [FIM(II)] spin reorientation (SR) transition and a giant magnetoresistance (MR) associated first-order ferrimagnetic(II)-to-antiferromagnetic (AFM) phase transition upon cooling, resulting in the AFM ground state with a weak in-plane net moment. Upon increasing the doping level from x = 0.01 to 0.1, both the SR transition and the first-order magnetic transition are suppressed. For x = 0.1, the former transition is suppressed, leaving only the Q-FIM(I)-to-AFM transition within the whole temperature region. TAFM-FIM shows almost similar changes upon the application of either in-plane or out-of-plane magnetic fields. TAFM-FIM values of the x = 0.01 and 0.04 samples are much higher than those of the Mn2-xCrxSb bulk with similar doping levels, which can be understood by the clamping effect from STO substrates. For each thin-film sample, the MR effect is observed near TAFM-FIM and disappears in the high temperature Q-FIM(I) phase and low temperature AFM phase, indicating that MR is related to the spin-dependent electron scattering during the first-order magnetic phase transition. Based on the magnetotransport and magnetic data, a magnetic phase diagram is established for the Mn2-xCrxSb films in the low doping level region.

Correlation between deformation and total entropy change at the first-order magnetic transition of Fe2P-based magnetocaloric materials

While there is a growing consensus that lattice is an important source of entropy change at structural or elastic first-order magnetic transitions (FOMT) with finite volume change, the case of volume preserving transitions (ΔV = 0) remains more controversial. Here, the evolution of the total transition entropy change within the Fe2P family is presented as a function of the discontinuity on the ratio of the cell parameters. A striking correlation between ΔStr and Δ(c/a) is observed. This relationship is a first step towards a systematization of the FOMT properties in the Fe2P materials system. It also demonstrates that deformation can play a leading role in volume preserving FOMT.

Effect of magnetic phase coexistence on spin-phonon coupling and magnetoelectric effect in polycrystalline Sm0.5Y0.5Fe0.58Mn0.42O3

The various physical properties with their intercorrelations in polycrystalline samples of Sm0.5Y0.5Fe0.58Mn0.42O3 [SYFM (58–42)] were investigated. The dc magnetization measurements revealed a weak ferromagnetic (WFM) transition at TÑ361 K that is followed by an incomplete spin reorientation (SR) transition at TSR1∼ 348 K. A first order magnetic transition (FOMT) around TSR2 ∼ 292 K completes the spin reorientation transition and the material enters into a nearly collinear antiferromagnetic (AFM) state. Robust magnetodielectric (MD) is found to be present in material at room temperature. True ferroelectric transition with TFE = 108 K and having a value of saturation polarization (∼0.06 μC/cm2 at 15 K) have been found in the specimen. This spin phonon coupling (SPC) stabilizes the ferroelectric state and responsible for magnetoelectric coupling (ME). We argue that wave vector (q) dependence of the spin-pair correlation affects the electronic and magnetodielectric properties in a similar way.

Unusual first-order magnetic phase transition and large magnetocaloric effect in Nd2In

A large magnetocaloric effect with its maximum near the boiling point of natural gas occurs in a rare-earth intermetallic compound ${\mathrm{Nd}}_{2}\mathrm{In}$. While behaviors of physical properties indicate that paramagnetic-ferromagnetic transformation supporting the large magnetocaloric effect is first order in nature, temperature-dependent crystallographic study reveals no changes in lattice symmetry and lack of discontinuities either in phase volume or lattice parameters. The borderline first-order nature of phase transformation in ${\mathrm{Nd}}_{2}\mathrm{In}$ is markedly different from conventional first-order magnetic transitions occurring in other members of the family -- isostructural ${\mathrm{Pr}}_{2}\mathrm{In}$ and nonisostructural ${\mathrm{Eu}}_{2}\mathrm{In}$.

Anisotropic magnetization and electronic structure of the first-order ferrimagnet ErCo2 studied by polarization dependent hard X-ray photoemission spectroscopy

The first-order ferrimagnet ErCo2 attracts interest not only because of metamagnetism and magnetocaloric effect just above TC ≈ 32–34 K but also because it is closely related with the itinerant metamagnetism of YCo2 and LuCo2. We study the electronic structure of single crystals with hard X-ray photoemission spectroscopy (HAXPES). Magnetization measurements reconfirm the first-order magnetic transition, metamagnetism, and strong magnetic anisotropy. Calculated ErCo2 band structures of the ferrimagnetic and paramagnetic phases are presented in detail. In the ferrimagnetic state, the density of states just below EF is smaller than in the paramagnetic phase. Valence band spectra in the paramagnetic state show strong polarization dependence. Furthermore, the change across the first-order ferrimagnetic transition in the valence band electronic structures is observed. These experimental data are well described by the band structure calculation incorporated with the polarization dependent cross-sections of orbitals. We further discuss possible effects of electron correlation and spin fluctuation.

Effect of the heat treatment on the microstructure, magnetism and magnetocaloric effect in Fe-rich (Mn,Fe)y(P,Si) melt-spun ribbons

The effect of the heat treatment on the magnetism, magnetocaloric effect and microstructure formation has been systematically studied in Fe-rich (Mn,Fe)y(P,Si) melt-spun ribbons (1.80 ≤ y ≤ 2.00). XRD, SEM and EDS measurements demonstrate that a metal deficiency prompts the stable (Mn,Fe)Si phase, whereas in the metal-rich region the (Mn,Fe)3Si phase is formed. It is found that the annealing temperature influences the composition and lattice parameters of the (Mn,Fe)y(P,Si) alloys, which greatly affects the Curie temperature (TC). For the optimal metal/non-metal ratio y the magnetic entropy change (|ΔSm|) is found to increase from 5.5 to 15.0 Jkg−1K−1 in a magnetic field change of 2 T by varying the annealing temperature from 1313 to 1433 K, indicating an enhancement of the first-order magnetic transition (FOMT). The presented results reveal that the secondary phase and magnetic properties in the (Mn,Fe)y(P,Si) system can be tuned by varying the annealing temperature and by adjusting the metal/non-metal ratio y.

Interplay of 3d and 4f electrons in ZrCuSiAs-type oxypnictide CeCrAsO

We investigated the physical properties of ZrCuSiAs-type oxypnictide CeCrAsO polycrystals by electrical transport, magnetic and thermodynamic measurements below room temperature. No superconductivity is found down to the lowest temperature measured (1.8 K). A first-order magnetic transition is consistently observed at . A Schottky anomaly is observed around 14 K and the ground-state doublet of Ce ions splits by 3.75 meV. It is suggested that the magnetic moments of Cr ions, which show long-range order above room temperature, reorient at . Meanwhile the generated internal magnetic field induces a short-range antiferromagnetic order of Ce moments, serving as a good probe for demonstrating the interplay between Cr-3 d and Ce-4 f electrons and further investigating the magnetism of Cr ions.

Peltier cell calorimetry “as an option” for commonplace cryostats: Application to the case of MnFe(P,Si,B) magnetocaloric materials

Peltier cell calorimetry is a powerful technique to record both the heat capacity and the latent heat, yet its availability is limited as it often requires homemade dedicated cryostats. Here, we describe the development of a Peltier cell differential scanning calorimeter facilitating the accessibility to the technique, since it is designed “as an option” for commonplace commercial cryostats equipped with high magnetic fields. This yields an apparatus well suited to detailed studies of magnetic transitions in general and of first-order magnetic transitions in particular. For magnetocaloric materials, our system can also be used to measure directly the isothermal entropy change ΔS induced by a magnetic field change; it even allows separating the cyclic (reversible) effect due to successive magnetization/demagnetization, which is the one relevant for applications, from the total magnetocaloric effect. To illustrate the versatility of this system, a thorough study of the ferromagnetic first-order transition of MnFe0.95P0.585Si0.34B0.075 is carried out. An exceptionally large cyclic entropy change at an intermediate field is observed in this compound, ΔScyclic = 13.2 J kg−1 K−1 for µ0ΔH = 1 T. This confirms that MnFe(P,Si,B) shows one of the most promising giant magnetocaloric effects to be used in emergent green technologies such as magnetocaloric cooling, heating or thermomagnetic waste heat recovery.

Limitations of scaling laws for determining the order of magnetic phase transitions in antiperovskite materials

For materials with magnetic phase transition, researchers have tried to find a simple magnetic method that can replace the calorimetric technique for determining the type of phase transition. Recently, the researchers provide a quantitative characteristic of first-order magnetic phase transitions, which is believed to have wide application prospect. The maximum exponent n, calculated from field dependence of magnetic entropy change, is>2 only for first-order phase transitions. This method has been tested in Bean-Rodbell model and for various types of materials with first-order phase transitions from ferromagnetic to paramagnetic or antiferromagnetic to ferromagnetic state. However, in this work, the determination of the order of phase transitions based on field dependence of magnetic entropy change contradicts the results of calorimetric measurements in antiperovskite compounds Mn3SnC and MnCu0.97N. This discrepancy may be associated with a first-order magnetic transition from ferrimagnetic to paramagnetic state in antiperovskite materials.

Effect of heat treatment on microstructure evolution and magnetocaloric properties of droplet melted Mn–Fe–P–Si alloys

Practical implementation of Mn–Fe–P–Si alloys requires not only excellent magnetocaloric but also mechanical properties. Although these properties can be improved by droplet melting process, the effect of heat treatment on droplets has not been clarified. An investigation has been carried out on the microstructure and magnetocaloric properties of Mn1.20Fe0.75P0.45Si0.55 droplets annealed at different conditions. Experimental results show that the as-cast sample is composed of Fe2P and (Mn,Fe)3Si phases. Tuning the annealing condition leads to fluctuations in Fe2P phase fraction and compositions, thereby affecting the magnetocaloric properties. Increasing the annealing temperature from 1273 to 1373 K, Curie temperature (TC) increases from 204.0 to 277.0 K, thermal hysteresis (ΔThys) reduces from 2.5 to 0.5 K, and isothermal entropy change (ΔSm) doubles to 18.5 J/(kg·K) under a 5 T field. The increase in annealing time leads to the 34.0% increase in TC to 301.5 K, the 66.7% decrease in ΔThys to 1.0 K, but the slight decrease in ΔSm to 11.9 J/(kg·K) at an annealing time of 8 h. The larger relative cooling power (RCP) at higher temperatures and longer times are related to the increase in the Fe2P fraction. Moreover, optimizing the heat treatment condition to 1373 K and 4 h makes the alloy lay at the ideal border of the first-order and second-order magnetic transition, thus obtaining high ΔSm (18.5 J/(kg·K)), large RCP (508.8 J/kg), and extremely low ΔThys (0.5 K) around room temperature. Consequently, this optimal processing produces a competitive candidate for near room temperature magnetic refrigeration.

Impact of F and S doping on (Mn,Fe)2(P,Si) giant magnetocaloric materials

The quarternary (Mn,Fe)2(P,Si)-based materials with a giant magnetocaloric effect (GMCE) at the ferromagnetic transition TC are promising bulk materials for solid-state magnetic refrigeration. In the present study we demonstrate that doping with the light elements fluorine and sulfur can be used to adjust TC near room temperature and tune the magnetocaloric properties. For F doping the first-order magnetic transition (FOMT) of Mn0.60Fe1.30P0.64Si0.36Fx (x = 0.00, 0.01, 0.02, 0.03) is enhanced, which is explained by an enhanced magnetoelastic coupling. The magnetic entropy change |ΔSm| at a field change (Δμ0H) of 2 T markedly improved by 30% from 14.2 Jkg−1K−1 (x = 0.00) at 335 K to 20.2 Jkg−1K−1 (x = 0.03) at 297 K. For the F doped material the value of |ΔSm| for Δμ0H = 1 T reaches 11.6 Jkg−1K−1 at 294 K, which is consistent with the calorimetric data (12.4 Jkg−1K−1). Neutron diffraction experiments reveal enhanced magnetic moments by F doping in agreement with the prediction of DFT calculation. For S doping in Mn0.60Fe1.25P0.66-ySi0.34Sy (y = 0.00, 0.01, 0.02, 0.03, 0.04) three impurity phases have been found from microstructural analysis, which reduce the stability of the FOMT in the main phase and decrease TC, e.g. the |ΔSm| reduces from 7.9(12.6) Jkg-1K-1 (332 K) for the undoped sample to 3.4(6.2) Jkg-1K-1 (313 K) for the maximum doped sample for Δμ0H = 1(2) T. Neutron diffraction experiments combined with first-principles theoretical calculation, distinguish the occupation of F/S dopants and the tuning mechanism for light element doping, corresponding to subtle structural changes and a strengthening of the covalent bonding between metal and metalloid atoms. It is found that the light elements F and S can effectively regulate the magnetocaloric properties and provide fundamental understanding of (Mn,Fe)2(P,Si)-based intermetallic compounds.

Enhancement of Magnetic Properties and Magnetocaloric Effects for Mn0.975Fe0.975P0.5Si0.5 Alloys by Optimizing Quenching Temperature

The effect of quenching temperature on phase structure and magnetocaloric properties of the Mn0.975Fe0.975P0.5Si0.5 alloys are systematically studied by X‐ray diffraction, scanning electron microscope, differential scanning calorimetry, and vibrating sample magnetometer. The Mn0.975Fe0.975P0.5Si0.5 alloys quenched at 1323, 1073, 873, and 673 K are all crystallized in the hexagonal Fe2P‐type phase and the phase fraction of the Fe2P phase increases with the decreases of quenching temperature. As the quenching temperature decreases from 1323 to 673 K, the crystal lattice of alloys expands and the atoms' occupation is more ordered, while the saturation magnetic moment increases from 3.71 to 4.10 μB f.u.−1 The values of thermal hysteresis increase linearly from 30 to 41 K when the quenching temperature is down to 673 K. This enhancement of the first‐order magnetic transition (FOMT) yields the maximum value of magnetic entropy change at 5 T increasing by 36%. To obtain excellent comprehensive properties for (Mn,Fe)2(P,Si) alloys, the methods of doping B element in the Mn0.975Fe0.975P0.5Si0.5 alloy are employed to tune the magnetocaloric properties. The results provide insights and systematic understanding into the effect of quenching temperature on the magnetocaloric properties of (Mn,Fe)2(P,Si)‐based alloys.

Effects of the Substitution of 20% Nd for La or Doping with 20% C on the Magnetic Properties and Magnetocaloric Effect in LaFe11.5Si1.5 Compound

The effects of element substitution and element doping on the magnetic properties and magnetocaloric effect of the LaFe11.5Si1.5 compound were investigated. The crystals of the LaFe11.5Si1.5, La0.8Nd0.2Fe11.5Si1.5, and LaFe11.5Si1.5C0.2 compounds all showed cubic NaZn13-type structures, but the lattice of the La0.8Nd0.2Fe11.5Si1.5 shrank and the lattice of the LaFe11.5Si1.5C0.2 expanded. All three compounds had the characteristic of first-order magnetic transition due to the obvious itinerant-electron metamagnetic (IEM) transition occurring above Curie temperature (TC). For the LaFe11.5Si1.5, La0.8Nd0.2Fe11.5Si1.5, and LaFe11.5Si1.5C0.2 compounds, the TC were approximately 194 K, 188 K, and 232 K, respectively. Meanwhile, the maximum magnetic entropy changes (−ΔSM) under a magnetic field change of 0–3 T were approximately 18.7 J/kg·K, 22.8 J/kg·K, and 16.4 J/kg·K, respectively. The TC was mainly affected by the lattice constant. Furthermore, the −ΔSM was mainly affected by the latent heat of the first-order magnetic transition.

Comparative study on the effect of synthesis route on the structural, magnetic, and magnetocaloric properties of La0 .5Ca0.5Mn0.95V0.05O3 manganite

ABSTRACT The influence of the synthesis method on structural, magnetic and magnetocaloric properties of the La0.5Ca0.5Mn0.95V0.05O3 compound has been investigated. The compound was prepared by glycine nitrate process (GNP) and compared to counterparts obtained with solid-state route (S-S) and ball milling (B-M). The structural analysis shows a pure and single-orthorhombic crystalline phase for the GNP compound. A secondary phase LaVO4 was detected for S-S and B-M samples. From magnetization versus temperature analysis, different magnetic behaviors were distinguished when moving from one technique to another. The nature of transition was determined and a crossover from second order to first-order magnetic transition was observed with the decrease of crystallite size. Landau theory was performed to confirm the order of magnetic transition of the sample consistent with the Banerjee criterion. The magnetic entropy change (ΔSm) and the relative cooling power RCP, which decreased by reducing the particle size, were calculated.

Enhanced reversibility of the magnetoelastic transition in (Mn,Fe)2(P,Si) alloys via minimizing the transition-induced elastic strain energy

• Generalized relationship: hysteresis v.s. transition-induced elastic strain energy. • Hysteresis reduced by 91% after replacement of Fe by 4 at.% Mo in (Mn,Fe)2(P,Si). • Reversible adiabatic temperature change enhanced by 500 via 4 at.% Mo substitution. • Spin-lattice-electron coupling dominate magnetoelastic transition in (Mn,Fe)2(P,Si). Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications. (Mn,Fe) 2 (P,Si) alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition, while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles. In the present work, we performed a comprehensive study on the magnetoelastic transition of the (Mn,Fe) 2 (P,Si) alloys by high-resolution transmission electron microscopy, in situ field- and temperature-dependent neutron powder diffraction as well as density functional theory calculations (DFT). We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the (Mn,Fe) 2 (P,Si) family. The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.% substitution of Fe by Mo in the Mn 1.15 Fe 0.80 P 0.45 Si 0.55 alloy. This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy. The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties, compared to the parent alloy. Based on the DFT calculations and the neutron diffraction experiments, we also elucidated the underlying mechanism of the tunable transition temperature for the (Mn,Fe) 2 (P,Si) family, which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling. The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.

Quenching of spin-orbit coupling and signature of Griffiths Phase in nanocrystalline La0.6Ba0.4MnO3 perovskite manganite

The size-dependent structural and magnetic properties of nano and bulk samples of 40 ​mol% Ba2+-doped LaMnO3 (i.e., La0.6Ba0.4MnO3) manganite have been investigated in detail. The Rietveld refinement of X-ray diffraction data confirms that nano and bulk La0.6Ba0.4MnO3 manganites crystallize into ideal cubic perovskite structure with Pm3¯m space group. The refined unit cell parameters decrease with increasing calcinations temperature or particle size. The temperature dependent magnetization measurements reveal that both the bulk and nano samples exhibit paramagnetic (PM) to ferromagnetic (FM) phase transition at Curie temperature (TC). A distinct bifurcation between magnetization curves under zero-field cooled (MZFC) and field-cooled (MFC) measurements reveals the possible existence of frustrated magnetic ordering or spin glass clusters. For nano sample, a sharp downward deviation in inverse susceptibility from Curie-Weiss law is observed, which indicates the existence of Griffiths Phase. The analysis of the field dependent magnetization M(H) curves measured at 10 ​K, in terms of saturation moments, reveals that there is a coupling between spin and orbital magnetic moments, in bulk sample of La0.6Ba0.4MnO3 manganite, which can be quenched by reducing particle size of the manganite. According to the Banerjee's criterion, nano sample exhibits first-order magnetic transition and bulk sample shows second-order magnetic transition in the low magnetic field region.

Reconfigurable single-material Peltier effect using magnetic-phase junctions

Peltier effects, which produce a heat flux at the junction of two different materials, have been an important technology for heating and cooling by electrical means. Whereas Peltier devices have advantages such as cleanliness, silence, compactness, flexibility, reliability, and efficiency, relatively complicated modular structures are unavoidable, leading to a higher cost than that of commonly used refrigeration technology. Here, we provide a concept of a Peltier device composed of a single magnetic material exhibiting a first-order magnetic transition. Our concept is based on a controllable junction structure consisting of two magnetic phases with opposite Peltier coefficients instead of a semiconductor junction. Using {mathrm{Mn}}_{1.96}{mathrm{Cr}}_{0.04}mathrm{Sb} samples with the first-order magnetic transition between ferrimagnetic (FI) and antiferromagnetic (AF) states, we successfully made a stable junction structure of AF/FI/AF by a pulse heating method and achieved a maximum Peltier coefficient of 0.58 mV. Our device concept was further verified by a numerical simulation based on a finite element method. The single-material Peltier effect reported here avoids a complex device design involving material junctions and is importantly reconfigurable.

Effects of carbon doping on structure and magnetocaloric properties of Mn1.25Fe0.7P0.5Si0.5 alloys

Abstract (Mn,Fe)2(P,Si)-basedmaterials are promisingly applied in the room-temperature magnetic refrigeration field. In this study, Mn1.25Fe0.7P0.5Si0.5Cx (x = 0, 0.01, 0.03 and 0.05) alloys were prepared by arc-melting and then a two-stage sintering process. The effects of C doping on the crystal structure and magnetocaloric behavior are discussed. Results indicate that the Fe2P-type structure (space group of P62 m) was crystallized for all samples with weakened first-order magnetic transitions (FOMT). The Curie temperature could be altered from 223.5 K to 278.5 K with the large magnetocaloric effect (MCE) remaining by C doping. In the applied magnetic field of 5 T, the peak value of magnetic entropy change (–ΔS M) increased by 7.3% to reach 25.1 J × kg–1 × K–1. The temperature-induced entropy change (ΔS DSC) derived from DSC was slightly larger than ΔS M induced by the magnetic field. The Mn1.25Fe0.7P0.5Si0.5 alloys with large MCE can be effectively tuned by C doping because C atoms prefered to share the substitute and occupy the interstitial sites in hexagonal Fe2P-type structure.

The correlation between the covalent bonds and magnetocaloric properties of the Mn2−xFexPyGe1−yMz compounds

In recent years, MnFePGe magnetocaloric materials have been widely studied as promising candidates for magnetic refrigeration materials. The Curie temperature of MnFePGe can be adjusted to around room temperature by changing the element ratio or doping with other elements. Due to its first-order magnetic and structural transition, it engenders a large entropy change but unfortunately also exhibits a large thermal hysteresis during the phase transition, which leads to energy loss and lower refrigeration capability. In this paper, we establish a correlation between the in-plane covalent bonding and Curie temperature (TC), thermal hysteresis (ΔThys), two-phase coexistence zone (ΔTcoex), and entropy change (ΔSDSC) using 54 Mn2−xFexPyGe1−yMz (where M is a metallic or nonmetallic doped element) samples with different components. Neutron diffraction and XRD diffraction data and refinements have been employed to allow a detailed electron density reconstruction of six typical samples with the maximum entropy method. We find that the length of the in-plane bonding is closely correlated with the TC and ΔThys, while the TC, ΔThys, ΔTcoex, and ΔSDSC have no significant correlation with the length of the interlayer covalent bond. Moreover, we find that the ΔThys correlates most strongly with the change in the bond length when undergoing the paramagnetic-to-ferromagnetic phase transition rather than the absolute value of the bond length. These results provide an understanding of how to control the properties, enabling effective ways to tune the composition of magnetic refrigeration materials to tailor magnetocaloric properties for optimal performance.

Magnetic-field-induced ferroelectric states in centrosymmetric R2BaCuO5 ( R=Dy and Ho)

The linear magnetoelectric effect and multiferroicity phenomena occur independently due to breaking inversion symmetry below the magnetically ordered state of either transition metal or rare-earth ions. Here, we report the occurrence of a linear magnetoelectric effect and magnetic field-induced ferromagnetism and ferroelectricity below ${T}_{\mathrm{N}}^{R}$ in the orthorhombic green phases ${R}_{2}\mathrm{BaCu}{\mathrm{O}}_{5}$ ($R=\mathrm{Dy}$ and Ho). They undergo a long-range antiferromagnetic ordering of ${\mathrm{Cu}}^{2+}$ (${T}_{\mathrm{N}}^{\mathrm{Cu}}=18.5$ and 17.5 K) and ${R}^{3+}$ ions (${T}_{\mathrm{N}}^{\mathrm{Dy}}=10.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}}^{\mathrm{Ho}}=8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). The neutron diffraction study reveals that these compounds undergo a first-order magnetic transition from the high-temperature centrosymmetric antiferromagnetic phase (${P}_{\mathrm{b}}{112}_{1}/n$) to the low-temperature noncentrosymmetric phases $Pn{m}^{\ensuremath{'}}a$ (Dy) and $P{112}_{1}^{\ensuremath{'}}/a$ (Ho), which allow linear magnetoelectric coupling. This is consistent with field-induced electric polarization, below ${T}_{\mathrm{N}}^{R}$, which varies linearly up to \ensuremath{\sim}1.2 T. Above a critical field $({H}_{\mathrm{c}}>1.2\phantom{\rule{0.16em}{0ex}}\mathrm{T})$, both compounds exhibit metamagnetic transitions with magnetization close to the saturation value ${M}_{s} \ensuremath{\sim}10.1\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ (Dy) and $\ensuremath{\sim}11.8\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ (Ho) at 7 T. Above the metamagnetic transition, a new polar state appears with large electric polarization, indicating field-induced ferroelectricity. We discuss the important role of $4f\text{\ensuremath{-}}3d$ coupling in determining the ground state magnetic structure responsible for the magnetoelectric coupling in both compounds.