Transition metal oxides exhibit rich electrical and magnetic properties. The epitaxial strain plays a vital role to manipulate their magnetic ground state. In addition, Oxygen vacancies (Vo) are one of the most common point defects to play a key role in regulating the physicochemical properties of oxides. (1-4) 
In this context, LCO exhibits interesting phenomena in terms of the origin of magnetism.
In this work, Perovskite LaCoO3 (PV-LCO) films were grown at STO and LAO substrate. Then brownmillerite LaCoO2.5 (BM-LCO) films are formed by annealing in a vacuum at 450 °C for 4h and 500 °C for 4h, respectively. The XRD spectra show that there is no impurity phase during phase transitions, indicating that the films can be fully transformed. (Fig.1a) The magnetic properties were confirmed by SQUID-VSM. The 50-nm-thick PV-LCO film on STO exhibits an obvious ferromagnetism phase. (Fig.1b-c) The tensile strain leads to a decrease of ΔCF due to distortion of CoO6 octahedron, promotes the spin state transition. (5,6) 
However, the same thickness coherently strain film in compression on LAO exhibits extremely weak ferromagnetism. We anticipate the reason for this is because the eg orbitals are split into two separate energy levels due to existence of the JTD distortion, it is always accompanied by an increase of the bond distance rCo–O and suppression of CoO6 octahedral rotation and distortion. Interestingly, the BM-LCO shows no hysteresis loop. We believe the reason for this novel phenomenon is that the increase in ordered Vo leads to the expansion of the lattice, thus inhibiting the rotation and distortion of the CoO6 octahedron and causing the generation of anti-ferromagnetic behavior. (7,8)
In sum, we find that BM-LCO films in epitaxial strain and Vo ordering show no ferromagnetism. This phenomenon provided an effective way to regulate the physical properties of cobalt oxides. It would have a good application value in the fields of ion electrochemical sensors. 

**References:** 
(1) J. H. Ngai, F. J. Walker, and C. H. Ahn, Annual Review of Materials Research 44 (1), 1 (2014). 
(2) A. La Spina, P. Paolicchi, and A. Kryszczynska, Nature 428 (6981), 400 (2004). 
(3) J. Jeong, N. Aetukuri, and T. Graf, Science 339 (6126), 1402 (2013) 
(4) G.E. Sterbinsky, R. Nanguneri, and J.X. Ma, Ryan, Phys. Rev. Lett. 120 197201(2018). 
(5) Er-Jia Guo, Ryan D. Desautels, and David Keavney, Physical Rev B 75 (14) (2007). 
(6) Fuchs, D. C. Pinta, and T. Schwarz, Physic Rev. B 75, 144402 (2007). 
(7) D. Fuchs, E. Arac, and C. Pinta, Phys. Rev. B 77, 014434, (2008). 
(8) Q. Zhang, A. Gao, and F. Meng, Nat Commun 12(1), 1853 (2021). 

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Strain independent Regulation of Magnetic Properties by Topotactic Phase Transformation in LaCoO3 Thin Films

Structural changes and evolution taking place in ferrites with increasing processing temperature are crucial from their performance point of view. Three M-type hexaferrites were prepared using solid-state reaction at 650-1250 °C: SrFe12O19 (SrM), BaFe12O19 (BaM), and CaFe12O19 (CaM). The evolution of phases was studied with X-ray powder diffraction and thermogravimetry investigation. The structural studies reveal that the formation M-type phase begins at 820, 850, and 1200 °C, respectively, and different mid-phases of SrFe3-x, BaFe2O4, and CaFe2O4 were formed. The structural studies in all cases were successfully refined using the P63/mmc (No.194) space group but Ca2+ shrank the hexaferrite crystal lattice. Their magnetic properties were studied with respect to their composition and microstructure by scanning electron microscopy (SEM). The different phase evolution leading to the different magnetic properties of M-type hexaferrite were discussed in the present work. 
**References:** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/36c0fa25d7625bed31a1e2e1bc6aa2e9.png) 
Table 1 The phase evolution with the temperature of SrM, BaM and CaM

Understanding of the Phase Evolution with Temperature in Pure SrM, BaM and CaM

Controlling ion migration of transition metal oxide(TMO) to recast crystal structure and macroscopic properties is current research emphasis [1, 2], which has potential applications in solid fuel cells, resistance switching etc. Among cobalt-based TMO, B-site atom determines functionality, but oxygen atom is hard to ignored. Electronic structure of B-site atom is profoundly affected by oxygen content due to coupling of lattice, charge, orbit, and spin. Vacuum annealing is a stable method to extract O2--ions [3, 4]. 40nm La0.5Sr0.5CoO3(P-LSCO) film are grown on LSAT(100) substrate. Then films are respectively annealed at 400 centigrade for 2 hours(B-LSCO) and 500 centigrade for 35 hours(S-LSCO) to extract O2--ions. Fig. 1a shows soft X-ray absorption spectrum(XAS) for cobalt L-edge, and an obvious peak shift to low energy (L3-peak of S, B and P-LSCO appear at 782.2eV, 781.5eV and 780.4eV respectively) indicates continuous decrease in average valence states of Co and oxygen content during O2--ions extracting process. For XAS of oxygen K-edge (Fig. 1b), the A and C peaks, representing hybridization of Co-2p/3d and O-2p orbital, gradually decrease in three samples. While B-peak, which represents content of oxygen vacancy, exhibits an increasing trend, consistent with above results. As a result, dramatic magnetism transformation was observed in film upon annealing. Fig. 1c and 1d show magnetic moment-temperature(M-T) curves and magnetic moment- magnetic field (M-H) curves for three samples, demonstrating ferromagnetism(FM) with Tc~220K, antiferromagnetism(AFM) and ferromagnetism with Tc&gt;300K in P-LSCO, B-LSCO and S-LSCO, respectively. In sum, we achieved giant magnetic transformation from FM to AFM to FM accompanying with O2--ion migration in LSCO film by vacuum annealing, which provides idea for regulating physics properties by ion migration engineering.

![](https://assets.underline.io/uploads/markdown_image/1/image/2f9d13eeec602e127c33a77c98f889f5.jpg)

Fig. 1 XAS for a) cobalt L-edge, b) oxygen K-edge, c) M-T curve, d) M-H curve

Oxygen ion migration regulates magnetism in La0.5Sr0.5CoO3 film

Solid-state refrigeration materials have various thermal effects, among which the hydrostatic pressure is an economical and practical method to drive the barocaloric effect (BCE) of brittle materials[1,2]. The BCE is ubiquitous in first-order phase transition materials, and its packaging technology is not limited to the shape of the materials[3,4]. In the brittle magnetocaloric materials MnCoGe0.99In0.01, there is a low-pressure induced large reversible BCE near room temperature, which avoids part of the refrigeration capacity reduction caused by hysteresis loss[5]. Here, we report the BCE of MnCoGe0.99In0.01 at hydrostatic pressure of 1kbar by variable-pressure calorimetry. Fig.1a shows the temperature dependence of the heat capacity dQ/dT of MnCoGe0.99In0.01 at different hydrostatic pressures after baseline subtraction, it can be found that the thermal hysteresis (ΔThys) at 1bar is 8.8K and the phase transition temperature moves to lower temperature with the increase of pressure. The linear fitting relationship between the transformation temperature shifts with the pressure (dT/dP) is obtained according to the heating and cooling transformation temperature under different pressures, as shown in the inset of Fig. 1b. The dT/dP is -10.6K/kbar in the heating process and is -8.7K/kbar in the cooling process. The entropy curve S(T,P) of MnCoGe0.99In0.01 during heating and cooling process was obtained by the calorimetric curves(Fig. 1a) through the pressure-dependent integrations across the phase transition, as shown in Fig.1b. We evaluated the reversible parts (ΔSrev and ΔTrev) of entropy change ΔS and adiabatic temperature change ΔT at 1kbar from the overlapping of the irreversible ΔS and ΔT during application and removal of pressure, as shown in Fig.1c and 1d, where the shaded areas represent the ΔSrev and ΔTrev, respectively. The relative narrow ΔThys and high driving rate dT/dP under pressure are more conducive to achieve large ΔSrev and ΔTrev. The ΔSrev of 19J/kg K and ΔTrev of 2.9K within a temperature span of 56K at 1kbar have been achieved. The refrigeration capacity of MnCoGe0.99In0.01 at 1kbar is as high as 373J/kg K.

![](https://assets.underline.io/uploads/markdown_image/1/image/f5b2d3fe1b51b27d3f3361529defdc74.jpg)

Fig.1.For MnCoGe0.99In0.01, a)dQ/dT, b)S, c) ΔSrev, d)ΔTrev.

Large room-temperature reversible barocaloric effect in MnCoGe0.99In0.01 alloys at low pressure

Conventional vapor compression refrigeration encounters environmental problems. As an alternative, solid-state refrigeration based on magnetocaloric effect (MCE) or barocaloric effect (BCE) has attracted tremendous attentions for its environmental-friendly and energy-saving superiority. The core of solid-state refrigeration lies in the magnitude of the caloric effect of refrigerants. Increasing the caloric effect as much as possible is a long-term pursuit [1-5]. Here, we report a large enhancement of MCE and BCE by hydrostatic pressure in Co-doped La(Fe,Si)13, which has been regarded to be promising refrigerants since its discovery in 2000[1]. The maximal entropy change SMCE almost doubled under 11.31kbar while the SBCE under 9kbar increases more than three times (Figure 1c and 1d). To disclose the essence from the atomic level, neutron powder diffractions were performed (Figure 1a). The results reveal that hydrostatic pressure sharpens the magnetoelastic transition and enlarges the volume change wherein through impacting the intra-icosahedral Fe-Fe bonds (B1, B2, B3) rather than the inter-icosahedral ones (B4, B5) in the NaZn13-type structure [1]. Such result is distinct from the case introducing chemical pressure by H atoms in the La(Fe,Si)13-based compounds, which can adjust phase transition temperature, but not the sharpness of phase transition and the MCE. To understand the mechanism, first-principles calculations are performed (Figure 1b), which offers a theoretical support for the hydrostatic pressure enhanced magnetovolume effect and the evolution from second-order to first-order transition [1]. The present study proves the enormous potential of enhancing caloric effect through influencing the specific atomic environments by pressure, which is also useful to achieve other pressure-related effects, such as controllable negative thermal expansion.

![](https://assets.underline.io/uploads/markdown_image/1/image/192f971b3efb1d85cc2c7296c0334dc7.jpg)

Hydrostatic Pressure Induced Giant Enhancement of the Solid-state Caloric Effect in the Rare-earth-based Giant Magnetocaloric Materials

Hydrostatic Pressure Induced Giant Enhancement of the Solid-state Caloric Effect in the Rare-earth-based Giant Magnetocaloric Materials

Pressure sensor (PS) has important application in artificial intelligence and modern industries. Baromagnetic effect (BME), i.e., pressure-induced magnetic moment change, is regarded as the candidate technology for new PS. The reported large BME in Mn3Ga0.95N0.94[1] has gained great attention. The origin comes from the pressure-induced spin re-orientation from Γ5g antiferromagnetic (AFM) to M-1 ferrimagnetic phase. Recently, the ternary metallic compounds MM’X (M, M’ = transition metals, X = main elements) have attracted renewed attention due to their barocaloric effect[2], and giant negative thermal expansion[3]. In the MM’X family, previous research indicated that the AFM coupling of the stoichiometric MnNiGe is very robust. The substitution of Mn with Fe introduces Fe-Mn ferromagnetic (FM) coupling, which can help to establish a cone-spiral magnetic coupling[4]. Hence, a new cycloidal spiral AFM structure (CyS-AFMb) was discovered in Mn0.87Fe0.13NiGe[5], which is sensitive to magnetic field and stress. As a result, a giant BME was achieved. The employed Mn0.87Fe0.13NiGe alloy were prepared by arc-melting technique. The CyS-AFMb was discovered in Mn0.87Fe0.13NiGe below 150 K. A low magnetic field can make the CyS-AFMb transform to a conical spiral FM with angle 70°(70°-CoS-FMb), accompanied by a step rise of magnetization (Fig.1). More importantly, the new CyS-AFMb is no longer insensitive to stress compared to the MnNiGe without Fe-doping. A pressure higher than 4kbar induces abnormal change of Mn(Fe)-Mn(Fe) distances hence transform the CyS-AFMb into a conical spiral ferromagnetic configuration(45°-CoS-FMa) with easily magnetized but much shortened magnetic moment (Fig.2). As a result, giant BME was observed under either a low magnetic field or a field of 2T~5T. The maximal BMC appears to be ~5.34 emu/g*kbar under 0.35T while ~9.03emu/g*kbar under 2.2T in a wide temperature range, which all far exceed those of the previous reported Mn3Ga0.95N0.94.

![](https://assets.underline.io/uploads/markdown_image/1/image/09482e36daa9f397642695bac745587e.jpg)

Fig.1. a)M-H curve at 5K with the sketch of spin structure evolution with H, b)Variable magnetic field NPD patterns at 5K, and c)phase diagram.

![](https://assets.underline.io/uploads/markdown_image/1/image/40c700b274a5a459169e05205fd24437.jpg)

Fig.2. The sketch of a)the CyS-AFMb andb)the 45°-CoS-FMa, and the variable pressure NPD patterns at 120K.

A new spin structure and giant baromagnetic effect in Mn0.87Fe0.13NiGe alloy

**Please click on the poster to see the abstract or leave your comment to the author.** 
**Session Chair:** Ying-Hao Chu, *National Yang Ming Chiao Tung University*

BPA: Multiferroics, Magnetoelectrics, Complex Oxides and Half-Metallics

poster

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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Please register for the MMM 2022 conference to join the event.

MMM 2022

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

**Please click on the poster to see the abstract or leave your comment to the author.** 
**Session Chair:** Xin Tang, *NIMS*

KPD: Hard Magnetic Materials VII: Nanostructured, Composite and Other Hard Magnetic Materials (Including Intermetallic Alloys and L10 Alloys)

**Session chair:** Jing Wang, The Institute of Physics, Chinese Academy of Sciences


BOC - Magnetoelectronic Materials and Phenomena: Complex Oxides

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

2022 Joint MMM-INTERMAG

**Session chairs:** SN Piramanayagam, Nanyang Technological University and Radhika Barua, Virginia Commonwealth University



FOC - Magnetoelastics and Magnetooptics

**Session chair:** Feiran Shen, Institute of Physics, Chinese Academy of Sciences


Baogen Shen

6

8

Presentations

Strain independent Regulation of Magnetic Properties by Topotactic Phase Transformation in LaCoO3 Thin Films

Understanding of the Phase Evolution with Temperature in Pure SrM, BaM and CaM

Oxygen ion migration regulates magnetism in La0.5Sr0.5CoO3 film

Large room-temperature reversible barocaloric effect in MnCoGe0.99In0.01 alloys at low pressure

Hydrostatic Pressure Induced Giant Enhancement of the Solid-state Caloric Effect in the Rare-earth-based Giant Magnetocaloric Materials

A new spin structure and giant baromagnetic effect in Mn0.87Fe0.13NiGe alloy

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