A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.

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Multiferroic and magnetoelectric materials

Recent research activities on the linear magnetoelectric (ME) effect?induction of magnetization by an electric field or of polarization by a magnetic field?are reviewed. Beginning with a brief summary of the history of the ME effect since its prediction in 1894, the paper focuses on the present revival of the effect. Two major sources for 'large' ME effects are identified. (i) In composite materials the ME effect is generated as a product property of a magnetostrictive and a piezoelectric compound. A linear ME polarization is induced by a weak ac magnetic field oscillating in the presence of a strong dc bias field. The ME effect is large if the ME coefficient coupling the magnetic and electric fields is large. Experiments on sintered granular composites and on laminated layers of the constituents as well as theories on the interaction between the constituents are described. In the vicinity of electromechanical resonances a ME voltage coefficient of up to 90?V?cm?1?Oe?1 is achieved, which exceeds the ME response of single-phase compounds by 3?5 orders of magnitude. Microwave devices, sensors, transducers and heterogeneous read/write devices are among the suggested technical implementations of the composite ME effect. (ii) In multiferroics the internal magnetic and/or electric fields are enhanced by the presence of multiple long-range ordering. The ME effect is strong enough to trigger magnetic or electrical phase transitions. ME effects in multiferroics are thus 'large' if the corresponding contribution to the free energy is large. Clamped ME switching of electrical and magnetic domains, ferroelectric reorientation induced by applied magnetic fields and induction of ferromagnetic ordering in applied electric fields were observed. Mechanisms favouring multiferroicity are summarized, and multiferroics in reduced dimensions are discussed. In addition to composites and multiferroics, novel and exotic manifestations of ME behaviour are investigated. This includes (i) optical second harmonic generation as a tool to study magnetic, electrical and ME properties in one setup and with access to domain structures; (ii) ME effects in colossal magnetoresistive manganites, superconductors and phosphates of the LiMPO4 type; (iii) the concept of the toroidal moment as manifestation of a ME dipole moment; (iv) pronounced ME effects in photonic crystals with a possibility of electromagnetic unidirectionality. The review concludes with a summary and an outlook to the future development of magnetoelectrics research.

https://iopscience.iop.org/article/10.1088/0022-3727/38/8/R01/pdf

Revival of the Magnetoelectric Effect

BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Physics and Applications of Bismuth Ferrite

The Conservation of Orbital Symmetry

Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

Why Are There so Few Magnetic Ferroelectrics

https://www.europeanurology.com/article/S0302-2838(07)01145-1/pdf/eau-guidelines-on-prostate-cancer

EAU guidelines on prostate cancer

OBJECTIVES To present a summary of the 2007 version of the European Association of Urology (EAU) guidelines on prostate cancer (PCa). METHODS A literature review of the new data emerging from 2004 to 2007 was performed by the working panel. The guidelines have been updated, and the level of evidence/grade of recommendation was added to the text based on a systematic review of the literature, which included a search of online databases and bibliographic reviews. RESULTS A full version is available at the EAU Office or at www.uroweb.org. Systemic prostate biopsy under ultrasound guidance is the preferred diagnostic method. Active treatment is mostly recommended for patients with localized disease and a long life expectancy, with radical prostatectomy being shown to be superior to watchful waiting in a prospective randomized trial. Nerve-sparing radical prostatectomy represents the approach of choice in organ-confined disease; neoadjuvant androgen deprivation demonstrates no improvement of outcome variables. Radiation therapy should be performed with at least 72 and 78 Gy in low-risk and intermediate- to high-risk PCa, respectively. Monotherapeutic androgen deprivation is the standard of care in metastatic PCa; intermittent androgen deprivation might be an alternative treatment option for selected patients. Follow-up is largely based on prostate-specific antigen and a disease-specific history with imaging only indicated when symptoms occur. Cytotoxic therapy with docetaxel has emerged as the reference treatment for metastatic hormone-refractory PCa. CONCLUSIONS The knowledge in the field of PCa is rapidly changing. These EAU guidelines on PCa summarize the most recent findings and put them into clinical practice.

/pdf/eau-guidelines-on-prostate-cancer-2s3es8pcpa.pdf

Ferroelectricity and weak ferromagnetism have been found to set on simultaneously in Ni3B7O13I at about 64°K. This is evidenced by dielectric hysteresis, spontaneous Faraday effect, quadratic magnetoelectric hysteresis, etc. The strong coupling between the mutually perpendicular spontaneous polarization—[001]—and spontaneous magnetization—[110]—is such that, when the former is reversed, the latter turns by 90°. The magnetic point group is most probably m′m2′. Dielectric constant, magnetic, and magnetoelectric susceptibilities and magnetic coercive field are shown as a function of temperature.

/pdf/some-properties-of-ferromagnetoelectric-nickel-iodine-27jyc31mtg.pdf

Some Properties of Ferromagnetoelectric Nickel‐Iodine Boracite, Ni3B7O13I

By means of the quadratic magnetoelectric effect the components of the non-linear magnetoelectric susceptibility tensor βijk of the antiferromagnetic ferroelectric ferroelastic phase of BiFeO3 have been determined at 4 K: β_111 =5010^-19[sA^-1],β_113=8110^-19[sA^-1], β_311 =0310^-19[sA^-1],β_333=2110^-19[sA^-1]

https://iopscience.iop.org/article/10.7567/JJAPS.24S2.1051/pdf

Measurement of the Quadratic Magnetoelectric Effect on Single Crystalline BiFeO3

2, 6-Dimethylphenyl propargyl ether (10) and its derivatives 12–15 rearrange thermally to 1, 5-dimethyl-6-methylene-tricyclo [3.2.1.02,7]oct-3-en-8-one (9) and related compounds 16–19. The ethers undergo first an aromatic [3, 3]-sigmatropic rearrangement to ortho-allenyldienones 11, which then undergo ring closure to the tricyclic products by an electrocyclic reaction.



Only in the case of the γ-methylpropargyl ether 13, the ortho-dienone 11 is further rearranged in low yield to the para-butynylphenol 20, but the tricyclic ketone 17 is again the main product.



New data show that the known thermal cyclisation of aryl propargyl ethers to chromenes (e. g. 4 8) involves a preliminary [3, 3]-sigmatropic rearrangement.

Sigmatropische Umlagerungen von Aryl‐propargyläthern; Synthese von 1, 5‐Dimethyl‐6‐methylen‐tricyclo[3, 2, 1, 02,7]‐oct‐3‐en‐8‐on‐Derivaten. Vorläufige Mitteilung

Hans Schmid

Papers

EAU guidelines on prostate cancer

EAU guidelines on prostate cancer

Some Properties of Ferromagnetoelectric Nickel‐Iodine Boracite, Ni3B7O13I

Measurement of the Quadratic Magnetoelectric Effect on Single Crystalline BiFeO3

Sigmatropische Umlagerungen von Aryl‐propargyläthern; Synthese von 1, 5‐Dimethyl‐6‐methylen‐tricyclo[3, 2, 1, 02,7]‐oct‐3‐en‐8‐on‐Derivaten. Vorläufige Mitteilung